MAX1471ATJ

19-3272; Rev 1; 3/05 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver General Description The MAX1471 low-power, CMOS, superheterodyne, RF dual-channel receiver is designed to receive both amplitude-shift-keyed (ASK) and frequency-shift-keyed (FSK) data without reconfiguring the device or introducing any time delay normally associated with changing modulation schemes. The MAX1471 requires few external components to realize a complete wireless RF digital data receiver for the 300MHz to 450MHz ISM bands. The MAX1471 includes all the active components required in a superheterodyne receiver including: a lownoise amplifier (LNA), an image-reject (IR) mixer, a fully integrated phase-locked loop (PLL), local oscillator (LO), 10.7MHz IF limiting amplifier with received-signalstrength indicator (RSSI), low-noise FM demodulator, and a 3V voltage regulator. Differential peak-detecting data demodulators are included for both the FSK and ASK analog baseband data recovery. The MAX1471 includes a discontinuous receive (DRX) mode for lowpower operation, which is configured through a serial interface bus. The MAX1471 is available in a 32-pin thin QFN package and is specified over the automotive -40°C to +125°C temperature range. Features ♦ ASK and FSK Demodulated Data on Separate Outputs ♦ Specified over Automotive -40°C to +125°C Temperature Range ♦ Low Operating Supply Voltage Down to 2.4V ♦ On-Chip 3V Regulator for 5V Operation ♦ Low Operating Supply Current 7mA Continuous Receive Mode 1.1µA Deep-Sleep Mode ♦ Discontinuous Receive (DRX) Low-Power Management ♦ Fast-On Startup Feature < 250µs ♦ Integrated PLL, VCO, and Loop Filter ♦ 45dB Integrated Image Rejection ♦ RF Input Sensitivity* ASK: -114dBm FSK: -108dBm ♦ Selectable IF BW with External Filter ♦ Programmable Through Serial User Interface ♦ RSSI Output and High Dynamic Range with AGC *0.2% BER, 4kbps, Manchester-encoded data, 280kHz IF BW MAX1471 Applications Automotive Remote Keyless Entry (RKE) Tire Pressure Monitoring Systems Garage Door Openers Wireless Sensors Wireless Keys Security Systems Medical Systems Home Automation Local Telemetry Systems Ordering Information PART MAX1471ATJ TEMP RANGE -40°C to +125°C PIN-PACKAGE 32 Thin QFN-EP** **EP = Exposed pad. Pin Configuration PDMAXA ADATA HVIN SCLK CS 32 DSADSA+ OPA+ DFA XTAL2 XTAL1 AVDD LNAIN 31 30 29 28 27 26 25 24 23 22 21 DVDD DGND DFF OPF+ DSF+ DSFPDMAXF PDMINF 1 2 3 4 5 6 7 8 9 LNASRC MAX1471 FDATA TOP VIEW PDMINA DIO 20 19 18 17 10 LNAOUT 11 MIXIN+ 12 MIXIN- 13 MIXOUT 14 AGND 15 IFIN- 16 IFIN+ THIN QFN ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 ABSOLUTE MAXIMUM RATINGS High-Voltage Supply, HVIN to DGND .......................-0.3V, +6.0V Low-Voltage Supply, AVDD and DVDD to AGND .....-0.3V, +4.0V SCLK, DIO, CS, ADATA, FDATA ....................................(DGND - 0.3V) to (HVIN + 0.3V) All Other Pins.............................(AGND - 0.3V) to (AVDD + 0.3V) Continuous Power Dissipation (TA = +70°C) 32-Pin Thin QFN (derate 21.3mW/°C above +70°C) ...1702mW Operating Temperature Range .........................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) ................................ +300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. DC ELECTRICAL CHARACTERISTICS (Typical Application Circuit, AVDD = DVDD = HVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = HVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER GENERAL CHARACTERISTICS Supply Voltage (5V) Supply Voltage (3V) HVIN VDD AVDD and DVDD unconnected from HVIN, but connected together HVIN, AVDD, and DVDD connected to power supply Operating TA < +85°C Polling duty cycle: 10% duty cycle DRX mode OFF current Deep-sleep current Operating Supply Current IDD TA < +105°C (Note 2) Polling duty cycle: 10% duty cycle DRX mode OFF current Deep-sleep current Operating TA < +125°C (Note 2) Polling duty cycle: 10% duty cycle DRX mode OFF current Deep-sleep current Startup Time tON Time for final signal detection, does not include baseband filter settling (Note 2) 200 4.5 2.4 5.0 3.0 7.0 705 5.0 1.1 5.5 3.6 8.4 855 14.2 7.1 8.5 865 15.5 13.4 8.6 900 44.1 36.4 250 µs µA mA µA mA µA V V mA SYMBOL CONDITIONS MIN TYP MAX UNITS DIGITAL OUTPUTS (DIO, ADATA, FDATA) Output High Voltage Output Low Voltage DIGITAL INPUTS (CS, DIO, SCLK) Input High Threshold Input Low Threshold VIH VIL 0.9 x HVIN . 0.1 x HVIN V V VOH VOL ISOURCE = 250µA (Note 2) ISINK = 250µA (Note 2) HVIN 0.15 0.15 V V 2 _______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver DC ELECTRICAL CHARACTERISTICS (continued) (Typical Application Circuit, AVDD = DVDD = HVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = HVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER Input-High Leakage Current Input-Low Leakage Current Input Capacitance VOLTAGE REGULATOR Output Voltage VREG HVIN = 5.0V, ILOAD = 7.0mA 3.0 V SYMBOL IIH IIL CIN (Note 2) (Note 2) (Note 2) CONDITIONS MIN TYP MAX -20 20 2.0 UNITS µA µA pF MAX1471 AC ELECTRICAL CHARACTERISTICS (Typical Application Circuit, AVDD = DVDD = HVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = HVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER GENERAL CHARACTERISTICS Receiver Sensitivity Maximum Receiver Input Power Level Receiver Input Frequency Range Receiver Image Rejection LNA/MIXER (Note 4) LNA Input Impedance Voltage Conversion Gain (HighGain Mode) Input-Referred 3rd-Order Intercept Point (High-Gain Mode) Voltage Conversion Gain (LowGain Mode) Input-Referred 3rd-Order Intercept Point (Low-Gain Mode) LO Signal Feedthrough to Antenna Mixer Output Impedance IF Input Impedance Operating Frequency 3dB Bandwidth FM DEMODULATOR Demodulator Gain GFM 2.2 mV/kHz Z11 fIF 330 10.7 10 Ω MHz MHz ZOUT Z11 Normalized to 50Ω fRF = 315MHz fRF = 434MHz 1 - j4.7 1 - j3.4 47.5 -38 12.2 -5 -90 330 dB dBm dB dBm dBm Ω RFIN 0.2% BER, 4kbps Manchester Code, 280kHz IF BW, 50Ω ASK FSK -114 dBm -108 0 300 (Note 3) 45 450 dBm MHz dB SYMBOL CONDITIONS MIN TYP MAX UNITS RFMAX fRF IR _______________________________________________________________________________________ 3 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 AC ELECTRICAL CHARACTERISTICS (continued) (Typical Application Circuit, AVDD = DVDD = HVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at AVDD = DVDD = HVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER ANALOG BASEBAND Maximum Data Filter Bandwidth Maximum Data Slicer Bandwidth Maximum Peak Detector Bandwidth Maximum Data Rate CRYSTAL OSCILLATOR Crystal Frequency Frequency Pulling by VDD Maximum Crystal Inductance Crystal Load Capacitance DIGITAL INTERFACE TIMING (see Figure 8) Minimum SCLK Setup to Falling Edge of CS Minimum CS Falling Edge to SCLK Rising-Edge Setup Time Minimum CS Idle Time Minimum CS Period Maximum SCLK Falling Edge to Data Valid Delay Minimum Data Valid to SCLK Rising-Edge Setup Time Minimum Data Valid to SCLK Rising-Edge Hold Time Minimum SCLK High Pulse Width Minimum SCLK Low Pulse Width Minimum CS Rising Edge to SCLK Rising-Edge Hold Time Maximum CS Falling Edge to Output Enable Time Maximum CS Rising Edge to Output Disable Time tSC tCSS tCSI tCS tDO tDS tDH tCH tCL tCSH tDV tTR 30 30 125 2.125 80 30 30 100 100 30 25 25 ns ns ns µs ns ns ns ns ns ns ns ns fXTAL 9.04 3 50 3 13.728 MHz ppm/V µH pF BWDF BWDS BWPD Manchester coded Nonreturn to zero (NRZ) 50 100 50 33 66 kHz kHz kHz kbps SYMBOL CONDITIONS MIN TYP MAX UNITS Note 1: Note 2: Note 3: Note 4: Production tested at TA = +85°C. Guaranteed by design and characterization over entire temperature range. Guaranteed by design and characterization. Not production tested. The oscillator register (0x3) is set to the nearest integer result of fXTAL / 100kHz (see the Oscillator Frequency Register section). Input impedance is measured at the LNAIN pin. Note that the impedance at 315MHz includes the 15nH inductive degeneration from the LNA source to ground. The impedance at 434MHz includes a 10nH inductive degeneration connected from the LNA source to ground. The equivalent input circuit is 50Ω in series with 2.2pF. The voltage conversion gain is measured with the LNA input matching inductor, the degeneration inductor, and the LNA/mixer resonator in place, and does not include the IF filter insertion loss. 4 _______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Typical Operating Characteristics (Typical Application Circuit, AVDD = DVDD = HVIN = +3.0V, fRF = 434MHz, TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1471 toc01 MAX1471 SUPPLY CURRENT vs. RF FREQUENCY MAX1471 toc02 DEEP-SLEEP CURRENT vs. TEMPERATURE MAX1471 toc03 8.0 +105°C 7.6 SUPPLY CURRENT (mA) +85°C +125°C 8.0 7.8 7.6 SUPPLY CURRENT (mA) 7.4 7.2 7.0 6.8 6.6 6.4 6.2 -40°C +25°C +125°C +105°C +85°C 12 10 DEEP-SLEEP CURRENT (µA) 8 6 4 2 0 7.2 6.8 +25°C 6.4 -40°C 6.0 2.4 2.7 3.0 SUPPLY VOLTAGE (V) 3.3 3.6 6.0 300 325 350 375 400 425 450 RF FREQUENCY (MHz) -40 -15 10 35 60 85 110 TEMPERATURE (°C) BIT-ERROR RATE vs. AVERAGE INPUT POWER (ASK DATA) MAX1471 toc04 BIT-ERROR RATE vs. AVERAGE INPUT POWER (FSK DATA) MAX1471 toc05 SENSITIVITY vs. TEMPERATURE (ASK DATA) 280kHz IF BW 0.2% BER MAX1471 toc06 100 280kHz IF BW 100 280kHz IF BW FREQUENCY DEVIATION = ±50kHz -102 -105 SENSITIVITY (dBm) -108 -111 -114 -117 -120 10 BIT-ERROR RATE (%) BIT-ERROR RATE fRF = 434MHz 10 fRF = 434MHz 1 0.2% BER 0.1 fRF = 315MHz 1 0.2% BER 0.1 fRF = 315MHz fRF = 434MHz fRF = 315MHz 0.01 -123 -121 -119 -117 -115 -113 -111 AVERAGE INPUT POWER (dBm) 0.01 -115 -113 -110 -108 -105 AVERAGE INPUT POWER (dBm) -40 -15 10 35 60 85 110 TEMPERATURE (°C) SENSITIVITY vs. TEMPERATURE (FSK DATA) MAX1471 toc07 SENSITIVITY vs. FREQUENCY DEVIATION (FSK DATA) MAX1471 toc08 RSSI vs. RF INPUT POWER AGC HYSTERESIS: 3dB 1.4 1.2 1.0 RSSI (V) 0.8 0.6 HIGH-GAIN MODE AGC SWITCH POINT MAX1471 toc09 -102 -104 SENSITIVITY (dBm) 280kHz IF BW 0.2% BER FREQUENCY DEVIATION = ±50kHz -98 -100 SENSITIVITY (dBm) -102 -104 -106 -108 -110 280kHz IF BW 0.2% BER 1.6 -106 fRF = 434MHz -108 fRF = 315MHz -110 0.4 0.2 0 1 10 FREQUENCY DEVIATION (kHz) 100 -130 -110 -90 -70 -50 -30 RF INPUT POWER (dBm) -10 10 LOW-GAIN MODE -112 -40 -15 10 35 60 85 110 TEMPERATURE (°C) -112 _______________________________________________________________________________________ 5 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Typical Operating Characteristics (continued) (Typical Application Circuit, AVDD = DVDD = HVIN = +3.0V, fRF = 434MHz, TA = +25°C, unless otherwise noted.) FSK DEMODULATOR OUTPUT vs. IF FREQUENCY MAX1471 toc11 RSSI AND DELTA vs. IF INPUT POWER 2.1 1.8 RSSI 1.5 RSSI (V) 1.2 0.9 0.6 0.3 0 -90 -70 -50 -30 -10 10 RF INPUT POWER (dBm) DELTA 1.5 DELTA (%) 0.5 -0.5 -1.5 -2.5 -3.5 0 10.4 MAX1471 toc10 SYSTEM VOLTAGE GAIN vs. IF FREQUENCY UPPER SIDEBAND MAX1471 toc12 3.5 FSK DEMODULATOR OUTPUT (V) 2.5 2.0 60 50 SYSTEM GAIN (dB) 40 30 20 10 0 -10 45dB IMAGE REJECTION 1.6 1.2 FROM RFIN TO MIXOUT fRF = 434MHz 0.8 0.4 LOWER SIDEBAND 10.5 10.6 10.7 10.8 10.9 11.0 0 5 10 15 20 25 30 IF FREQUENCY (MHz) IF FREQUENCY (MHz) IMAGE REJECTION vs. TEMPERATURE MAX1471 toc13 NORMALIZED IF GAIN vs. IF FREQUENCY MAX1471 toc14 S11 LOG-MAGNITUDE PLOT WITH MATCHING NETWORK OF RFIN (434MHz) MAX1471 toc15 48 fRF = 315MHz 5 NORMALIZED IF GAIN (dBm) 46 IMAGE REJECTION (dB) 0 10dB/ div 44 fRF = 434MHz 42 -5 0dB -10 0dB 40 -15 434MHz -16.4dB 1 10 IF FREQUENCY (MHz) 100 START: 50MHz STOP: 1GHz 38 -40 -15 10 35 60 85 110 TEMPERATURE (°C) -20 S11 SMITH CHART OF RFIN (434MHz) MAX1471 toc16 500MHz 200MHz 6 _______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Typical Operating Characteristics (continued) (Typical Application Circuit, AVDD = DVDD = HVIN = +3.0V, fRF = 434MHz, TA = +25°C, unless otherwise noted.) INPUT IMPEDANCE vs. INDUCTIVE DEGENERATION 90 80 70 REAL IMPEDANCE (Ω) 60 50 40 30 20 10 0 1 10 INDUCTIVE DEGENERATION (nH) REAL IMPEDANCE IMAGINARY IMPEDANCE fRF = 315MHz L1 = 0nH MAX1471 toc17 INPUT IMPEDANCE vs. INDUCTIVE DEGENERATION -125 -150 IMAGINARY IMPEDANCE (Ω) -175 -200 -225 -250 -275 -300 -325 -350 100 REAL IMPEDANCE (Ω) 90 80 70 60 50 40 30 20 10 0 1 10 INDUCTIVE DEGENERATION (nH) REAL IMPEDANCE IMAGINARY IMPEDANCE fRF = 434MHz L1 = 0nH MAX1471 toc18 -125 -150 -175 -200 -225 -250 -275 -300 -325 IMAGINARY IMPEDANCE (Ω) -350 100 PHASE NOISE vs. OFFSET FREQUENCY MAX1471 toc19 PHASE NOISE vs. OFFSET FREQUENCY fRF = 434MHz MAX1471 toc20 -50 -60 PHASE NOISE (dBc/Hz) -70 -80 -90 -100 -110 -120 fRF = 315MHz -50 -60 PHASE NOISE (dBc/Hz) -70 -80 -90 -100 -110 -120 100 1k 10k 100k 1M 10M 100 1k 10k 100k 1M 10M OFFSET FREQUENCY (Hz) OFFSET FREQUENCY (Hz) Pin Description PIN 1 2 3 4 5 NAME DSADSA+ OPA+ DFA XTAL2 Inverting Data Slicer Input for ASK Data Noninverting Data Slicer Input for ASK Data Noninverting Op-Amp Input for the ASK Sallen-Key Data Filter Data-Filter Feedback Node. Input for the feedback of the ASK Sallen-Key data filter. 2nd Crystal Input FUNCTION _______________________________________________________________________________________ 7 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Pin Description (continued) PIN 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 EP NAME XTAL1 AVDD LNAIN LNASRC LNAOUT MIXIN+ MIXINMIXOUT AGND IFINIFIN+ PDMINF PDMAXF DSFDSF+ OPF+ DFF DGND DVDD FDATA CS DIO SCLK HVIN ADATA PDMINA PDMAXA GND 1st Crystal Input Analog Power-Supply Voltage for RF Sections. AVDD is connected to an on-chip +3.0V low-dropout regulator. Decouple to AGND with a 0.1µF capacitor. Low-Noise Amplifier Input Low-Noise Amplifier Source for External Inductive Degeneration. Connect an inductor to AGND to set LNA input impedance. Low-Noise Amplifier Output. Connect to mixer through an LC tank filter. Differential Mixer Input. Must be AC-coupled to driving input. Differential Mixer Input. Bypass to AGND with a capacitor. 330Ω Mixer Output. Connect to the input of the 10.7MHz IF filter. Analog Ground Differential 330Ω IF Limiter Amplifier Input. Bypass to AGND with a capacitor. Differential 330Ω IF Limiter Amplifier Input. Connect to output of the 10.7MHz IF filter. Minimum-Level Peak Detector for FSK Data Maximum-Level Peak Detector for FSK Data Inverting Data Slicer Input for FSK Data Noninverting Data Slicer Input for FSK Data Noninverting Op-Amp Input for the FSK Sallen-Key Data Filter Data-Filter Feedback Node. Input for the feedback of the FSK Sallen-Key data filter. Digital Ground Digital Power-Supply Voltage for Digital Sections. Connect to AVDD. Decouple to DGND with a 10nF capacitor. Digital Baseband FSK Demodulator Data Output Active-Low Chip-Select Input Serial Data Input/Output Serial Interface Clock Input High-Voltage Supply Input. For 3V operation, connect HVIN to AVDD and DVDD. Digital Baseband ASK Demod Data Output Minimum-Level Peak Detector for ASK Output Maximum-Level Peak Detector for ASK Output Exposed Paddle. Connect to ground. FUNCTION 8 _______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Functional Diagram LNAOUT 10 MIXIN+ 11 MIXIN12 IMAGE REJECTION 0° MAX1471 MIXOUT IFIN13 15 IFIN+ 16 IF LIMITING AMPS LNAIN 8 LNA Σ LNASRC 9 90° RSSI CRYSTAL OSCILLATOR DIVIDE BY 32 PHASE DETECTOR VCO ASK RDF1 100kΩ 4 RDF2 100kΩ 3 2 OPA+ DSA+ DFA AGND 14 XTAL1 XTAL2 6 5 LOOP FILTER CS 26 DIO 27 SCLK 28 DVDD 24 DGND 23 SERIAL INTERFACE, CONTROL REGISTERS, AND POLLING TIMER FSK FSK DEMODULATOR ASK DATA FILTER 31 PDMINA RDF1 100kΩ RDF2 100kΩ 32 PDMAXA 1 FSK DATA FILTER DSA- HVIN 29 AVDD 7 3.0V REG 3.0V 30 ADATA MAX1471 25 FDATA 19 DSF- 18 PDMAXF 17 PDMINF 20 DSF+ 21 OPF+ 22 DFF _______________________________________________________________________________________ 9 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Detailed Description The MAX1471 CMOS superheterodyne receiver and a few external components provide a complete ASK/FSK receive chain from the antenna to the digital output data. Depending on signal power and component selection, data rates as high as 33kbps using Manchester Code (66kbps nonreturn to zero) can be achieved. The MAX1471 is designed to receive binary FSK or ASK data on a 300MHz to 450MHz carrier. ASK modulation uses a difference in amplitude of the carrier to represent logic 0 and logic 1 data. FSK uses the difference in frequency of the carrier to represent a logic 0 and logic 1. Automatic Gain Control (AGC) When the AGC is enabled, it monitors the RSSI output. When the RSSI output reaches 1.28V, which corresponds to an RF input level of approximately -64dBm, the AGC switches on the LNA gain reduction attenuator. The attenuator reduces the LNA gain by 35dB, thereby reducing the RSSI output by about 0.55V. The LNA resumes high-gain mode when the RSSI output level drops back below 0.68V (approximately -67dBm at the RF input) for a programmable interval called the AGC dwell time. The AGC has a hysteresis of approximately 3dB. With the AGC function, the RSSI dynamic range is increased, allowing the MAX1471 to reliably produce an ASK output for RF input levels up to 0dBm with a modulation depth of 18dB. AGC is not necessary and can be disabled when utilizing only the FSK data path. The MAX1471 features an AGC lock controlled by the AGC lock bit (see Table 8). When the bit is set, the LNA is locked in its present gain state. Low-Noise Amplifier (LNA) The LNA is a cascode amplifier with off-chip inductive degeneration that achieves approximately 28dB of voltage gain that is dependent on both the antenna-matching network at the LNA input, and the LC tank network between the LNA output and the mixer inputs. The off-chip inductive degeneration is achieved by connecting an inductor from LNASRC to AGND. This inductor sets the real part of the input impedance at LNAIN, allowing for a flexible match to low input impedances such as a PC board trace antenna. A nominal value for this inductor with a 50Ω input impedance is 15nH at 315MHz and 10nH at 434MHz, but the inductance is affected by PC board trace length. See the Typical Operating Characteristics to see the relationship between the inductance and input impedance. The inductor can be shorted to ground to increase sensitivity by approximately 1dB, but the input match is not optimized for 50Ω. The LC tank filter connected to LNAOUT comprises L2 and C9 (see the Typical Application Circuit). Select L2 and C9 to resonate at the desired RF input frequency. The resonant frequency is given by: f= 1 2π L TOTAL × CTOTAL Mixer A unique feature of the MAX1471 is the integrated image rejection of the mixer. This device was designed to eliminate the need for a costly front-end SAW filter for many applications. The advantage of not using a SAW filter is increased sensitivity, simplified antenna matching, less board space, and lower cost. The mixer cell is a pair of double-balanced mixers that perform an IQ downconversion of the RF input to the 10.7MHz intermediate frequency (IF) with low-side injection (i.e., fLO = fRF - fIF). The image-rejection circuit then combines these signals to achieve approximately 45dB of image rejection. Low-side injection is required as high-side injection is not possible due to the on-chip image rejection. The IF output is driven by a source follower, biased to create a driving impedance of 330Ω to interface with an off-chip 330Ω ceramic IF filter. The voltage conversion gain driving a 330Ω load is approximately 19.5dB. Note that the MIXIN+ and MIXIN- inputs are functionally identical. Phase-Locked Loop (PLL) The PLL block contains a phase detector, charge pump/integrated loop filter, voltage-controlled oscillator (VCO), asynchronous 32x clock divider, and crystal oscillator. This PLL does not require any external components. The relationship between the RF, IF, and reference frequencies is given by: fREF = (fRF - fIF)/32 To allow the smallest possible IF bandwidth (for best sensitivity), the tolerance of the reference must be minimized. where LTOTAL = L2 + LPARASITICS and CTOTAL = C9 + CPARASITICS. LPARASITICS and CPARASITICS include inductance and capacitance of the PC board traces, package pins, mixer input impedance, LNA output impedance, etc. These parasitics at high frequencies cannot be ignored, and can have a dramatic effect on the tank filter center frequency. Lab experimentation should be done to optimize the center frequency of the tank. 10 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver The IF section presents a differential 330Ω load to provide matching for the off-chip ceramic filter. It contains five AC-coupled limiting amplifiers with a bandpass-filter-type response centered near the 10.7MHz IF frequency with a 3dB bandwidth of approximately 10MHz. For ASK data, the RSSI circuit demodulates the IF to baseband by producing a DC output proportional to the log of the IF signal level with a slope of approximately 16mV/dB. For FSK, the limiter output is fed into a PLL to demodulate the IF. Intermediate Frequency (IF) is suppressed by the integrated quadrature imagerejection circuitry. For an input RF frequency of 315MHz, a reference frequency of 9.509MHz is needed for a 10.7MHz IF frequency (low-side injection is required). For an input RF frequency of 433.92MHz, a reference frequency of 13.2256MHz is required. The XTAL oscillator in the MAX1471 is designed to present a capacitance of approximately 3pF between the XTAL1 and XTAL2. If a crystal designed to oscillate with a different load capacitance is used, the crystal is pulled away from its stated operating frequency, introducing an error in the reference frequency. Crystals designed to operate with higher differential load capacitance always pull the reference frequency higher. In actuality, the oscillator pulls every crystal. The crystal’s natural frequency is really below its specified frequency, but when loaded with the specified load capacitance, the crystal is pulled and oscillates at its specified frequency. This pulling is already accounted for in the specification of the load capacitance. Additional pulling can be calculated if the electrical parameters of the crystal are known. The frequency pulling is given by: fp = where: fp is the amount the crystal frequency pulled in ppm. Cm is the motional capacitance of the crystal. Ccase is the case capacitance. Cspec is the specified load capacitance. Cload is the actual load capacitance. When the crystal is loaded as specified, i.e., Cload = Cspec, the frequency pulling equals zero. ⎞ Cm ⎛ 1 1 6 − ⎜ ⎟ × 10 2 ⎝ Ccase + Cload Ccase + Cspec ⎠ MAX1471 FSK Demodulator The FSK demodulator uses an integrated 10.7MHz PLL that tracks the input RF modulation and determines the difference between frequencies as logic-level ones and zeros. The PLL is illustrated in Figure 1. The input to the PLL comes from the output of the IF limiting amplifiers. The PLL control voltage responds to changes in the frequency of the input signal with a nominal gain of 2.2mV/kHz. For example, an FSK peak-to-peak deviation of 50kHz generates a 110mVP-P signal on the control line. This control line is then filtered and sliced by the FSK baseband circuitry. The FSK demodulator PLL requires calibration to overcome variations in process, voltage, and temperature. For more information on calibrating the FSK demodulator, see the Calibration section. The maximum calibration time is 120µs. In DRX mode, the FSK demodulator calibration occurs automatically just before the IC enters sleep mode. Crystal Oscillator The XTAL oscillator in the MAX1471 is used to generate the local oscillator (LO) for mixing with the received signal. The XTAL oscillator frequency sets the received signal frequency as: fRECEIVE = (fXTAL x 32) +10.7MHz The received image frequency at: fIMAGE = (fXTAL x 32) -10.7MHz TO FSK BASEBAND FILTER AND DATA SLICER IF LIMITING AMPS PHASE DETECTOR CHARGE PUMP LOOP FILTER 10.7MHz VCO 2.2mV/kHz Figure 1. FSK Demodulator PLL Block Diagram ______________________________________________________________________________________ 11 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 3.0V VDD ASK DATA OUT SCLK DIO C26 VDD CS FSK DATA OUT 32 PDMAXA 31 PDMINA 30 ADATA 29 HVIN 28 SLCK 27 DIO 26 CS 25 FDATA 1 C5 R3 2 3 C4 C3 VDD DVDD 24 C23 DGND DSA- VCC DSA+ OPA+ DFF 23 22 21 C22 C21 R8 4 C14 5 Y1 VDD C15 DFA OPF+ MAX1471 XTAL2 DSF+ DSFLNAOUT LNASRC MIXOUT MIXIN+ PDMAXF AGND IFIN+ IFINPDMINF 6 7 20 19 18 17 XTAL1 AVDD C27 C6 RF INPUT C7 8 LNAIN MIXIN- L1 9 10 11 C11 C9 12 C8 VDD L2 13 14 15 C12 16 L3 IN GND C10 Y2 OUT Figure 2. Typical Application Circuit Data Filters The data filters for the ASK and FSK data are implemented as a 2nd-order lowpass Sallen-Key filter. The pole locations are set by the combination of two onchip resistors and two external capacitors. Adjusting the value of the external capacitors changes the corner frequency to optimize for different data rates. The corner frequency in kHz should be set to approximately 1.5 times the fastest expected Manchester data rate in kbps from the transmitter. Keeping the corner frequency near the data rate rejects any noise at higher frequencies, resulting in an increase in receiver sensitivity. The configuration shown in Figure 3 can create a Butterworth or Bessel response. The Butterworth filter offers a very flat amplitude response in the passband 12 and a rolloff rate of 40dB/decade for the two-pole filter. The Bessel filter has a linear phase response, which works well for filtering digital data. To calculate the value of the capacitors, use the following equations, along with the coefficients in Table 2: CF1 = CF2 = b a(100k)( π)(fC ) a 4(100k)( π)(fC ) where fC is the desired 3dB corner frequency. For example, choose a Butterworth filter response with a corner frequency of 5kHz: ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 1. Component Values for Typical Application Circuit COMPONENT C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C14 C15 C21 C22 C23 C26 C27 L1 L2 L3 R3 R8 Y1 Y2 VALUE FOR 433.92MHz RF 220pF 470pF 0.047µF 0.1µF 100pF 100pF 1.0pF 220pF 100pF 1500pF 15pF 15pF 220pF 470pF 0.01µF 0.1µF 0.047µF 56nH 16nH 10nH 25kΩ 25kΩ 13.2256MHz 10.7MHz ceramic filter VALUE FOR 315MHz RF 220pF 470pF 0.047µF 0.1µF 100pF 100pF 2.2pF 220pF 100pF 1500pF 15pF 15pF 220pF 470pF 0.01µF 0.1µF 0.047µF 100nH 30nH 15nH 25kΩ 25kΩ 9.509MHz 10.7MHz ceramic filter DESCRIPTION (%) 10 5 10 10 5 5 ±0.1pF 10 5 10 5 5 10 5 10 10 10 Coilcraft 0603CS Coilcraft 0603CS 5 5 5 Crystal Murata SFECV10.7 series Note: Component values vary depending on PC board layout. CF1 = CF2 = 1.000 ≈ 450pF (1.414)(100kΩ)(3.14)(5kHz) (4)(100kΩ)(3.14)(5kHz) 1.414 ≈ 225pF Choosing standard capacitor values changes CF1 to 470pF and CF2 to 220pF. In the Typical Application Circuit, CF1 and CF2 are named C4 and C3, respectively, for ASK data, and C21 and C22 for FSK data. Data Slicers The purpose of a data slicer is to take the analog output of a data filter and convert it to a digital signal. This is achieved by using a comparator and comparing the analog input to a threshold voltage. The threshold voltage is set by the voltage on the DSA- pin for the ASK receive chain (DSF- for the FSK receive chain), which is connected to the negative input of the data slicer comparator. Numerous configurations can be used to generate the data-slicer threshold. For example, the circuit in Figure 4 shows a simple method using only one resistor and one capacitor. This configuration averages the analog output of the filter and sets the threshold to approximately 50% of that amplitude. With this configuration, the threshold automatically adjusts as the analog signal varies, minimizing the possibility for errors in the digital data. The sizes of R and C affect how fast the threshold tracks to the analog amplitude. Be sure to keep the corner frequency of the RC circuit much lower than the lowest expected data rate. ______________________________________________________________________________________ 13 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 2. Coefficients to Calculate CF1 and CF2 FILTER TYPE Butterworth (Q = 0.707) Bessel (Q = 0.577) a 1.414 1.3617 b 1.000 0.618 Figure 5 shows a configuration that uses the positive and negative peak detectors to generate the threshold. This configuration sets the threshold to the midpoint between a high output and a low output of the data filter. Peak Detectors The maximum peak detectors (PDMAXA for ASK, PDMAXF for FSK) and minimum peak detectors (PDMINA for ASK, PDMINF for FSK), in conjunction with resistors and capacitors shown in Figure 5, create DC output voltages proportional to the high and low peak values of the filtered ASK or FSK demodulated signals. The resistors provide a path for the capacitors to discharge, allowing the peak detectors to dynamically follow peak changes of the data-filter output voltages. The maximum and minimum peak detectors can be used together to form a data-slicer threshold voltage at a midvalue between the maximum and minimum voltage levels of the data stream (see the Data Slicers section and Figure 5). The RC time constant of the peakdetector combining network should be set to at least 5 times the data period. If there is an event that causes a significant change in the magnitude of the baseband signal, such as an AGC gain switch or a power-up transient, the peak detectors may “catch” a false level. If a false peak is detected, the slicing level is incorrect. The MAX1471 has a feature called peak-detector track enable (TRK_EN), where the peak-detector outputs can be reset (see Figure 6). If TRK_EN is set (logic 1), both the maximum and minimum peak detectors follow the input signal. When TRK_EN is cleared (logic 0), the peak detectors revert to their normal operating mode. The TRK_EN function is automatically enabled for a short time and then disabled whenever the IC recovers from the sleep portion of DRX mode, or when an AGC gain switch occurs. Since the peak detectors exhibit a fast attack/slow decay response, this feature allows for an extremely fast startup or AGC recovery. See Figure 7 for an illustration of a fast-recovery sequence. In addition to the automatic control of this function, the TRK_EN bits can be controlled through the serial interface (see the Serial Control Interface section). MAX1471 RSSI OR FSK DEMOD 100kΩ 100kΩ DSA+ DSF+ OPA+ OPF+ DFA DFF CF2 CF1 Figure 3. Sallen-Key Lowpass Data Filter MAX1471 DATA SLICER ADATA FDATA C DSADSFR DSA+ DSF+ Figure 4. Generating Data-Slicer Threshold Using a Lowpass Filter Power-Supply Connections The MAX1471 can be powered from a 2.4V to 3.6V supply or a 4.5V to 5.5V supply. The device has an on-chip linear regulator that reduces the 5V supply to 3V needed to operate the chip. To operate the MAX1471 from a 3V supply, connect DVDD, AVDD, and HVIN to the 3V supply. When using a 5V supply, connect the supply to HVIN only and con- With this configuration, a long string of NRZ zeros or ones can cause the threshold to drift. This configuration works best if a coding scheme, such as Manchester coding, which has an equal number of zeros and ones, is used. 14 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 MAX1471 DATA SLICER MAXIMUM PEAK DETECTOR MINIMUM PEAK DETECTOR ADATA FDATA PDMAXA PDMAXF C R R PDMINA PDMINF C Figure 5. Generating Data-Slicer Threshold Using the Peak Detectors MINIMUM PEAK DETECTOR PDMINA PDMINF BASEBAND FILTER TRK_EN = 1 MAXIMUM PEAK DETECTOR TO SLICER INPUT PDMAXA PDMAXF MAX1471 TRK_EN = 1 Figure 6. Peak-Detector Track Enable nect AVDD and DVDD together. In both cases, bypass DVDD and HVIN with a 0.01µF capacitor and AVDD with a 0.1µF capacitor. Place all bypass capacitors as close to the respective supply pin as possible. ______________________________________________________________________________________ 15 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Serial Control Interface Communication Protocol The MAX1471 can use a 4-wire interface or a 3-wire interface (default). In both cases, the data input must follow the timing diagrams shown in Figures 8 and 9. Note that the DIO line must be held LOW while CS is high. This is to prevent the MAX1471 from entering discontinuous receive mode if the DRX bit is high. The data is latched on the rising edge of SCLK, and therefore must be stable before that edge. The data sequencing is MSB first, the command (C[3:0]; see Table 3), the register address (A[3:0]; see Table 4) and the data (D[7:0]; see Table 5). The mode of operation (3-wire or 4-wire interface) is selected by DOUT_FSK and/or DOUT_ASK bits in the configuration register. Either of those bits selects the ASKOUT and/or FSKOUT line as a SERIAL data output. Upon receiving a read register command (0x2), the serial interface outputs the data on either pin, according to Figure 10. If neither of these bits are 1, the 3-wire interface is selected (default on power-up) and the DIO line is effectively a bidirectional input/output line. DIO is selected as an output of the MAX1471 for the following CS cycle whenever a READ command is received. The CPU must tri-state the DIO line on the cycle of CS that follows a read command, so the MAX1471 can drive the data output line. Figure 11 shows the diagram of the 3-wire interface. Note that the user can choose to send either 16 cycles of SCLK, as in the case of the 4wire interface, or just eight cycles, as all the registers are 8-bits wide. The user must drive DIO low at the end of the read sequence. The MASTER RESET command (0x3) (see Table 3) sends a reset signal to all the internal registers of the MAX1471 just like a power-off and power-on sequence tCS RECEIVER ENABLED, TRK_EN SET TRK_EN CLEARED MAX PEAK DETECTOR 200mV/div FILTER OUTPUT MIN PEAK DETECTOR DATA OUTPUT DATA OUTPUT 2V/div 100µs/div Figure 7. Fast Receiver Recovery in FSK Mode Utilizing Peak Detectors would do. The reset signal remains active for as long as CS is high after the command is sent. Continuous Receive Mode (DRX = 0) In continuous receive mode, individual analog modules can be powered on directly through the power configuration register (register 0x0). The SLEEP bit (bit 0) overrides the power settings of the remaining bits and puts the part into deep-sleep mode when set. It is also necessary to write the frequency divisor of the external crystal in the oscillator frequency register (register 0x3) to optimize image rejection and to enable accurate calibration sequences for the polling timer and the FSK demodulator. This number is the integer result of fXTAL / 100kHz. If the FSK receive function is selected, it is necessary to perform an FSK calibration to improve receive sensitivity. Polling timer calibration is not necessary. See the Calibration section for more information. tCSI CS tCSS tSC SCLK tDH tDI DIO HIGH-IMPEDANCE tDV HIGH-IMPEDANCE D7 D0 HI-Z tDO tTR tCL tCH tCSH DATA IN DATA OUT Figure 8. Digital Communications Timing Diagram 16 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 CS SCLK DIO C3 C2 C1 C0 A3 A2 A1 A0 D7 D6 D5 D4 DATA D3 D2 D1 D0 COMMAND ADDRESS Figure 9. Data Input Diagram CS SCLK DIO 0 0 1 0 A3 A2 A1 A0 0 0 0 0 DATA 0 0 0 0 C3 C2 C1 C0 A3 A2 A1 A0 D7 DATA D0 READ COMMAND ADDRESS COMMAND ADDRESS ADATA (IF DOUT_ASK = 1) R7 R6 R5 R4 R3 R2 R1 R0 R7 REGISTER DATA R0 REGISTER DATA FDATA (IF DOUT_FSK = 1) R7 R6 R5 R4 R3 R2 R1 R0 R7 REGISTER DATA R0 REGISTER DATA Figure 10. Read Command on a 4-Wire SERIAL Interface Discontinuous Receive Mode (DRX = 1) In the discontinuous receive mode (DRX = 1), the power signals of the different modules of the MAX1471 toggle between OFF and ON, according to internal timers tOFF, tCPU, and tRF. It is also necessary to write the frequency divisor of the external crystal in the oscillator frequency register (register 0x3). This number is the integer result of fXTAL / 100kHz. Before entering the discontinuous receive mode for the first time, it is also necessary to calibrate the timers (see the Calibration section). The MAX1471 uses a series of internal timers (tOFF, t CPU , and t RF ) to control its power-up. The timer sequence begins when both CS and DIO are one. The MAX1471 has an internal pullup on the DIO pin, so the user must tri-state the DIO line when CS goes high. The external CPU can then go to a sleep mode during tOFF. A high-to-low transition on DIO, or a low level on DIO serves as the wake-up signal for the CPU, which must then start its wake-up procedure, and drive DIO low before tLOW expires (tCPU + tRF). Once tRF expires, the MAX1471 enables the FSKOUT and/or ASKOUT data outputs. The CPU must then keep DIO low for as long as it may need to analyze any received data. Releasing DIO causes the MAX1471 to pull up DIO, reinitiating the tOFF timer. Oscillator Frequency Register (Address: 0x3) The MAX1471 has an internal frequency divider that divides down the crystal frequency to 100kHz. The MAX1471 uses the 100kHz clock signal when calibrating itself and also to set the image-rejection frequency. The hexadecimal value written to the oscillator frequency register is the nearest integer result of fXTAL / 100kHz. ______________________________________________________________________________________ 17 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 CS SCLK DIO 0 0 1 0 A3 A2 A1 A0 0 0 0 0 DATA 0 0 0 0 R7 R6 R5 R4 R3 R2 R1 R0 R7 REGISTER DATA R0 READ COMMAND ADDRESS REGISTER DATA 16 BITS OF DATA CS SCLK DIO 0 0 1 0 A3 A2 A1 A0 0 0 0 0 DATA 0 0 0 0 R7 R6 R5 R4 R3 R2 R1 A3 READ COMMAND ADDRESS REGISTER DATA 8 BITS OF DATA Figure 11. Read Command in 3-Wire Interface Table 3. Command Bits C[3:0] 0x0 0x1 0x2 0x3 0x4–0xF DESCRIPTION No operation Write data Read data Master reset Not used ister. To calculate the dwell time, use the following equation: Dwell Time = 2Reg0xA fXTAL where Reg 0xA is the value of register 0xA in decimal. To calculate the value to write to register 0xA, use the following equation and use the next integer higher than the calculated result: Reg 0xA ≥ 3.3 x log10 (Dwell Time x fXTAL) For Manchester Code (50% duty cycle), set the dwell time to at least twice the bit period. For nonreturn-tozero (NRZ) data, set the dwell to greater than the period of the longest string of zeros or ones. For example, using Manchester code at 315MHz (f XTAL = 9.509375MHz) with a data rate of 4kbps (bit period = 125µs), the dwell time needs to be greater than 250µs: Reg 0xA ≥ 3.3 x log10 (250µs x 9.509375MHz) ≈11.14 Choose the register value to be the next integer value higher than 11.14, which is 12 or 0x0C hex. The default value of the AGC dwell timer on power-up or reset is 0x0D. For example, if data is being received at 315MHz, the crystal frequency is 9.509375MHz. Dividing the crystal frequency by 100kHz and rounding to the nearest integer gives 95, or 0x5F hex. So for 315MHz, 0x5F would be written to the oscillator frequency register. AGC Dwell Timer Register (Address: 0xA) The AGC dwell timer holds the AGC in low-gain state for a set amount of time after the power level drops below the AGC switching threshold. After that set amount of time, if the power level is still below the AGC threshold, the LNA goes into high-gain state. This is important for ASK since the modulated data may have a high level above the threshold and a low level below the threshold, which without the dwell timer would cause the AGC to switch on every bit. The AGC dwell time is dependent on the crystal frequency and the bit settings of the AGC dwell timer reg- 18 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 4. Register Summary REGISTER A[3:0] 0x0 0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9 0xA REGISTER NAME Power configuration Configuration Control Oscillator frequency Off timer—tOFF (upper byte) Off timer—tOFF (lower byte) CPU recovery timer—tCPU RF settle timer—tRF (upper byte) RF settle timer—tRF (lower byte) Status register (read only) AGC dwell timer DESCRIPTION Enables/disables the LNA, AGC, mixer, baseband, peak detectors, and sleep mode (see Table 6). Sets options for the device such as output enables, off-timer prescale, and discontinuous receive mode (see Table 7). Controls AGC lock, peak-detector tracking, as well as polling timer and FSK calibration (see Table 8). Sets the internal clock frequency divisor. This register must be set to the integer result of fXTAL / 100kHz (see the Oscillator Frequency Register section). Sets the duration that the MAX1471 remains in low-power mode when DRX is active (see Table 10). Increases maximum time the MAX1471 stays in lower power mode while CPU wakes up when DRX is active (see Table 11). During the time set by the settle timer, the MAX1471 is powered on with the peak detectors and the data outputs disabled to allow time for the RF section to settle. DIO must be driven low at any time during tLOW = tCPU + tRF or the timer sequence restarts (see Table 12). Provides status for PLL lock, AGC state, crystal operation, polling timer, and FSK calibration (see Table 9). Controls the dwell (release) time of the AGC. Calibration The MAX1471 must be calibrated to ensure accurate timing of the off timer in discontinuous receive mode or when receiving FSK signals. The first step in calibration is ensuring that the oscillator frequency register (address: 0x3) has been programmed with the correct divisor value (see the Oscillator Frequency Register section). Next, enable the mixer to turn the crystal driver on. Calibrate the polling timer by setting POL_CAL_EN = 1 in the configuration register (register 0x1). Upon completion, the POL_CAL_DONE bit in the status register (register 0x8) is 1, and the POL_CAL_EN bit is reset to zero. If using the MAX1471 in continuous receive mode, polling timer calibration is not needed. FSK receiver calibration is a two-step process. Set FSKCALLSB = 1 (register 0x1) or to reduce the calibration time, accuracy can be sacrificed by setting the FSKCALLSB = 0. Next, initiate FSK receiver calibration, set FSK_CAL_EN = 1. Upon completion, the FSK_CAL_DONE bit in the status register (register 0x8) is one, and the FSK_CAL_EN bit is reset to zero. When in continuous receive mode and receiving FSK data, recalibrate the FSK receiver after a significant change in temperature or supply voltage. When in discontinuous receive mode, the polling timer and FSK receiver (if enabled) are automatically calibrated during every wake-up cycle. Off Timer (tOFF) The first timer, tOFF (see Figure 12), is a 16-bit timer that is configured using: register 0x4 for the upper byte, register 0x5 for the lower byte, and bits PRESCALE1 and PRESCALE0 in the configuration register (register 0x1). Table 10 summarizes the configuration of the tOFF timer. The PRESCALE1 and PRESCALE2 bits set the size of the shortest time possible (tOFF time base). The data written to the tOFF registers (0x4 and 0x5) is multiplied by the time base to give the total tOFF time. On power-up, the off timer registers are set to zero and must be written before using DRX mode. 19 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 5. Register Configuration ADDRESS A3 A2 A1 A0 POWER CONFIGURATION (0x0) 0000 CONFIGURATION (0x1) 0001 CONTROL (0x2) 0010 OSCILLATOR FREQUENCY (0x3) 0011 OFF TIMER (upper byte) (0x4) 0100 OFF TIMER (lower byte) (0x5) 0101 CPU RECOVERY TIMER (0x6) 0110 RF SETTLE TIMER (upper byte) (0x7) 0111 RF SETTLE TIMER (lower byte) (0x8) 1000 STATUS REGISTER (read only) (0x9) 1001 AGC DWELL TIMER (0xA) 1010 X X X dt4 dt3* dt2* dt1 dt0* LOCK DET AGCST CLK ALIVE X X X POL_CAL FSK_CAL _DONE _DONE t7 t6 t5 t4 t3 t2 t1 t0 t15 t14 t13 t12 t11 t10 t9 t8 t7 t6 t5 t4 t3 t2 t1 t0 t7 t6 t5 t4 t3 t2 t1 t0 t15 t14 t13 t12 t11 t10 t9 t8 d7 d6 d5 d4 d3 d2 d1 d0 X AGC LOCK X X FSKTRK_ ASKTRK_ EN EN POL_ CAL_EN FSK_CAL _EN X GAIN SET* FSKCALL SB FSK_ DOUT ASK_ DOUT TOFF_ PS1 TOFF_ PS0 DRX_ MODE LNA_EN AGC_EN MIXER_ EN FSKBB_ EN FSKPD_ EN ASKBB_ EN ASKPD_ EN SLEEP D7 D6 D5 D4 DATA D3 D2 D1 D0 *Power-up state = 1. All other bits, power-up state = 0. During tOFF, the MAX1471 is operating with very low supply current (5.0µA typ), where all of its modules are turned off, except for the tOFF timer itself. Upon completion of the tOFF time, the MAX1471 signals the user by asserting DIO low. CPU Recovery Timer (tCPU) The second timer, tCPU (see Figure 12), is used to delay the power-up of the MAX1471, thereby providing extra power savings and giving a CPU the time required to complete its own power-on sequence. The CPU is signaled to begin powering up when the DIO line is pulled low by the MAX1471 at the end of tOFF. tCPU then begins 20 counting down, while DIO is held low by the MAX1471. At the end of tCPU, the tRF counter begins. tCPU is an 8-bit timer, configured through register 0x6. The possible tCPU settings are summarized in Table 11. The data written to the tCPU register (0x6) is multiplied by 120µs to give the total tCPU time. On power-up, the CPU timer register is set to zero and must be written before using DRX mode. RF Settle Timer (tRF) The third timer, tRF (see Figure 12), is used to allow the RF sections of the MAX1471 to power up and stabilize before ASK or FSK data is received. tRF begins count- ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 6. Power Configuration Register (Address: 0x0) BIT ID LNA_EN AGC_EN MIXER_EN FSKBB_EN FSKPD_EN ASKBB_EN ASKPD_EN SLEEP BIT NAME LNA enable AGC enable Mixer enable FSK baseband enable FSK peak detector enable ASK baseband enable ASK peak detector enable Sleep mode BIT LOCATION (0 = LSB) 7 6 5 4 3 2 1 0 POWER-UP STATE 0 0 0 0 0 0 0 0 1 = Enable LNA 0 = Disable LNA 1 = Enable AGC 0 = Disable AGC 1 = Enable mixer 0 = Disable mixer 1 = Enable FSK baseband 0 = Disable FSK baseband 1 = Enable FSK peak detectors 0 = Disable FSK peak detectors 1 = Enable ASK baseband 0 = Disable ASK baseband 1 = Enable ASK peak detectors 0 = Disable ASK peak detectors 1 = Deep-sleep mode 0 = Normal operation FUNCTION ing once tCPU has expired. At the beginning of tRF, the modules selected in the power control register (register 0x0) are powered up with the exception of the peak detectors and have the tRF period to settle. At the end of tRF, the MAX1471 stops driving DIO low and enables ADATA, FDATA, and peak detectors if chosen to be active in the power configuration register (0x0). The CPU must be awake at this point, and must hold DIO low for the MAX1471 to remain in operation. The CPU must begin driving DIO low any time during tLOW = tCPU + tRF. If the CPU fails to drive DIO low, DIO is pulled high through the internal pullup resistor, and the timer sequence is restarted, leaving the MAX1471 powered down. Any time the DIO line is driven high while the DRX = 1, the DRX sequence is initiated, as defined in Figure 12. tRF is a 16-bit timer, configured through registers 0x7 (upper byte) and 0x8 (lower byte). The possible tRF settings are in Table 12. The data written to the tRF register (0x7 and 0x8) is multiplied by 120µs to give the total tRF time. On power-up, the RF timer registers are set to zero and must be written before using DRX mode. Typical Power-Up Procedure Here is a typical power-up procedure for receiving either ASK or FSK signals at 315MHz in continuous mode: 1) Write 0x3000 to reset the part. 2) Write 0x10FE to enable all RF and baseband sections. 3) Write 0x135F to set the oscillator frequency register to work with a 315MHz crystal. 4) Write 0x1120 to set FSKCALLSB for an accurate FSK calibration. 5) Write 0x1201 to begin FSK calibration. 6) Read 0x2900 and verify that bit 0 is 1 to indicate FSK calibration is done. The MAX1471 is now ready to receive ASK or FSK data. Due to the high sensitivity of the receiver, it is recommended that the configuration registers be changed only when not receiving data. Receiver desensitization may occur, especially if odd-order harmonics of the SCLK line fall within the IF bandwidth. ______________________________________________________________________________________ 21 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 7. Configuration Register (Address: 0x1) BIT ID X BIT NAME Don’t care BIT LOCATION (0 = LSB) 7 POWER-UP STATE 0 Don’t care. 0 = LNA low-gain state. 1 = LNA high-gain state. For manual gain control, enable the AGC (AGC_EN = 1), set LNA gain state to desired setting, then disable the AGC (AGC_EN = 0). FSKCALLSB = 1 enables a longer, more accurate FSK calibration. FSKCALLSB = 0 provides for a quick, less accurate FSK calibration. This bit enables the FDATA pin to act as the serial data output in 4-wire mode. (See the Communication Protocol section.) This bit enables the ADATA pin to act as the serial data output in 4-wire mode. (See the Communication Protocol section.) Sets LSB size for the off timer. (See the Off Timer section.) 1 = Discontinuous receive mode. (See the Discontinuous Receive Mode section.) 0 = Continuous receive mode. (See the Continuous Receive Mode section.) FUNCTION GAINSET Gain set 6 1 FSKCALLSB FSK accurate calibration 5 0 DOUT_FSK FSKOUT enable 4 0 DOUT_ASK TOFF_PS1 TOFF_PS0 ASKOUT enable Off-timer prescale Off-timer prescale 3 2 1 0 0 0 DRX_MODE Receive mode 0 0 Layout Considerations A properly designed PC board is an essential part of any RF/microwave circuit. On high-frequency inputs and outputs, use controlled-impedance lines and keep them as short as possible to minimize losses and radiation. At high frequencies, trace lengths that are on the order of λ/10 or longer act as antennas. Keeping the traces short also reduces parasitic inductance. Generally, 1in of a PC board trace adds about 20nH of parasitic inductance. The parasitic inductance can have a dramatic effect on the effective inductance of a passive component. For example, a 0.5in trace connecting a 100nH inductor adds an extra 10nH of inductance or 10%. To reduce the parasitic inductance, use wider traces and a solid ground or power lane below the signal traces. Also, use low-inductance connections to ground on all GND pins, and place decoupling capacitors close to all VDD or HVIN connections. 22 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 8. Control Register (Address: 0x2) BIT ID X AGCLOCK X FSKTRK_EN BIT NAME None AGC lock None FSK peak detector track enable ASK peak detector track enable BIT LOCATION (0 = LSB) 7 6 5, 4 3 0 POWER-UP STATE Don’t care 0 Don’t care. Locks the LNA gain in its present state. Don’t care. Enables the tracking mode of the FSK peak detectors when FSKTRK_EN = 1. (See the Peak Detectors section.) Enables the tracking mode of the ASK peak detectors when ASKTRK_EN = 1. (See the Peak Detectors section.) POL_CAL_EN = 1 starts the polling timer calibration. Calibration of the polling timer is needed when using the MAX1471 in discontinous receive mode. POL_CAL_EN resets when calibration completes properly. (See the Calibration section.) FSK_CAL_EN starts the FSK receiver calibration. FSK_CAL_EN resets when calibration completes properly. (See the Calibration section.) FUNCTION ASKTRK_EN 2 0 POL_CAL_EN Polling timer calibration enable 1 0 FSK_CAL_EN FSK calibration enable 0 0 Table 9. Status Register (Read Only) (Address: 0x9) BIT ID LOCKDET AGCST CLKALIVE X POL_CAL_DONE FSK_CAL_DONE BIT NAME Lock detect AGC state Clock/crystal alive None Polling timer calibration done FSK calibration done BIT LOCATION (0 = LSB) 7 6 5 4, 3, 2 1 0 FUNCTION 0 = Internal PLL is not locked so the MAX1471 will not receive data. 1 = Internal PLL is locked. 0 = LNA in low-gain state. 1 = LNA in high-gain state. 0 = No valid clock signal seen at the crystal inputs. 1 = Valid clock at crystal inputs. Don’t care. 0 = Polling timer calibraton in progress or not completed. 1 = Polling timer calibration is complete. 0 = FSK calibration in progress or not completed. 1 = FSK calibration is compete. ______________________________________________________________________________________ 23 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 CS DIO tOFF tOFF tCPU tCPU tLOW tRF tRF ADATA OR FDATA Figure 12. DRX Mode Sequence of the MAX1471 Table 10. Off-Timer (tOFF) Configuration PRESCALE1 0 0 1 1 PRESCALE0 0 1 0 1 tOFF TIME BASE (1 LSB) 120µs 480µs 1920µs 7680µs MIN tOFF REG 0x4 = 0x00 REG 0x5 = 0x01 120µs 480µs 1.92ms 7.68ms MAX tOFF REG 0x4 = 0xFF REG 0x5 = 0xFF 7.86s 31.46s 2 min 6s 8 min 23s Table 11. CPU Recovery Timer (tCPU) Configuration TIME BASE (1 LSB) 120µs MIN tCPU REG 0x6 = 0x01 120µs MAX tCPU REG 0x6 = 0xFF 30.72ms Chip Information TRANSISTOR COUNT: 21,344 PROCESS: CMOS Table 12. RF Settle Timer (tRF) Configuration TIME BASE (1 LSB) 120µs MIN tRF REG 0x7 = 0x00 REG 0x8 = 0x01 120µs MAX tRF REG 0x7 = 0xFF REG 0x8 = 0xFF 7.86s 24 ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) QFN THIN.EPS L MAX1471 D2 D D/2 MARKING k L E/2 E2/2 E (NE-1) X e C L C L b D2/2 0.10 M C A B XXXXX E2 PIN # 1 I.D. DETAIL A e (ND-1) X e e/2 PIN # 1 I.D. 0.35x45° DETAIL B e L1 L C L C L L e 0.10 C A 0.08 C e C A1 A3 PACKAGE OUTLINE, 16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm -DRAWING NOT TO SCALE- 21-0140 H 1 2 ______________________________________________________________________________________ 25 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) COMMON DIMENSIONS PKG. 16L 5x5 20L 5x5 28L 5x5 32L 5x5 40L 5x5 SYMBOL MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. EXPOSED PAD VARIATIONS PKG. CODES T1655-1 T1655-2 T1655N-1 T2055-2 T2055-3 T2055-4 T2055-5 T2855-1 T2855-2 T2855-3 T2855-4 T2855-5 T2855-6 T2855-7 T2855-8 T2855N-1 T3255-2 T3255-3 T3255-4 T3255N-1 T4055-1 D2 MIN. NOM. MAX. MIN. E2 NOM. MAX. L ±0.15 A A1 A3 b D E e k L DOWN BONDS ALLOWED 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0 0.02 0.05 0 0.02 0.05 0 0.02 0.05 0 0.02 0.05 0 0.02 0.05 0.20 REF. 0.20 REF. 0.25 0.30 0.35 0.25 0.30 0.35 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 0.80 BSC. 0.65 BSC. 0.25 - 0.25 0.20 REF. 0.20 REF. 0.20 0.25 0.30 0.20 0.25 0.30 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 0.50 BSC. 0.50 BSC. - 0.25 0.25 0.20 REF. 0.15 0.20 0.25 4.90 5.00 5.10 4.90 5.00 5.10 0.40 BSC. 0.25 0.35 0.45 3.00 3.00 3.00 3.00 3.00 3.00 3.15 3.15 2.60 3.15 2.60 2.60 3.15 2.60 3.15 3.15 3.00 3.00 3.00 3.00 3.20 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.10 3.20 3.00 3.25 3.25 2.70 3.25 2.70 2.70 3.25 2.70 3.25 3.25 3.10 3.10 3.10 3.10 3.35 3.35 2.80 3.35 2.80 2.80 3.35 2.80 3.35 3.35 3.20 3.20 3.20 3.20 3.15 3.15 2.60 3.15 2.60 2.60 3.15 2.60 3.15 3.15 3.00 3.00 3.00 3.00 3.10 3.10 3.10 3.10 3.10 3.10 3.25 3.25 2.70 3.25 2.70 2.70 3.25 2.70 3.25 3.25 3.10 3.10 3.10 3.10 3.30 3.20 3.20 3.20 3.20 3.20 3.20 3.35 3.35 2.80 3.35 2.80 2.80 3.35 2.80 3.35 3.35 3.20 3.20 3.20 3.20 3.40 ** ** ** ** ** ** 0.40 ** ** ** ** ** ** ** 0.40 ** ** ** ** ** ** NO YES NO NO YES NO YES NO NO YES YES NO NO YES YES NO NO YES NO NO YES 0.30 0.40 0.50 0.45 0.55 0.65 0.45 0.55 0.65 0.30 0.40 0.50 0.40 0.50 0.60 - 0.30 0.40 0.50 16 20 28 32 N 40 ND 4 5 7 8 10 4 5 7 8 10 NE WHHB WHHC WHHD-1 WHHD-2 ----JEDEC L1 NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220, EXCEPT EXPOSED PAD DIMENSION FOR T2855-1, T2855-3, AND T2855-6. 10. WARPAGE SHALL NOT EXCEED 0.10 mm. 11. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. 12. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. 13. LEAD CENTERLINES TO BE AT TRUE POSITION AS DEFINED BY BASIC DIMENSION "e", ±0.05. 3.30 3.40 3.20 ** SEE COMMON DIMENSIONS TABLE PACKAGE OUTLINE, 16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm -DRAWING NOT TO SCALE- 21-0140 H 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.