LTC2241-10

LTC2241-10 10-Bit, 210Msps ADC FEATURES n n n n n n n n n n n n n DESCRIPTION The LTC®2241-10 is a 210Msps, sampling 10-bit A/D converter designed for digitizing high frequency, wide dynamic range signals. The LTC2241-10 is perfect for demanding communications applications with AC performance that includes 60.5dB SNR and 78dB SFDR. Ultralow jitter of 95fsRMS allows IF undersampling with excellent noise performance. DC specs include ±0.3LSB INL (typ), ±0.15LSB DNL (typ) and no missing codes over temperature. The digital outputs can be either differential LVDS, or single-ended CMOS. There are three format options for the CMOS outputs: a single bus running at the full data rate or two demultiplexed buses running at half data rate with either interleaved or simultaneous update. A separate output power supply allows the CMOS output swing to range from 0.5V to 2.625V. The ENC+ and ENC – inputs may be driven differentially or single ended with a sine wave, PECL, LVDS, TTL, or CMOS inputs. An optional clock duty cycle stabilizer allows high performance over a wide range of clock duty cycles. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *LTC2220-1, LTC2220, LTC2221, LTC2230, LTC2231 are 3.3V parts. n Sample Rate: 210Msps 60.5dB SNR 78dB SFDR 1.2GHz Full Power Bandwidth S/H Single 2.5V Supply Low Power Dissipation: 585mW LVDS, CMOS, or Demultiplexed CMOS Outputs Selectable Input Ranges: ±0.5V or ±1V No Missing Codes Optional Clock Duty Cycle Stabilizer Shutdown and Nap Modes Data Ready Output Clock Pin Compatible Family 250Msps: LTC2242-12 (12-Bit), LTC2242-10 (10-Bit) 210Msps: LTC2241-12 (12-Bit), LTC2241-10 (10-Bit) 170Msps: LTC2240-12 (12-Bit), LTC2240-10 (10-Bit) 185Msps: LTC2220-1 (12-Bit)* 170Msps: LTC2220 (12-Bit), LTC2230 (10-Bit)* 135Msps: LTC2221 (12-Bit), LTC2231 (10-Bit)* 64-Pin 9mm × 9mm QFN Package APPLICATIONS n n n n Wireless and Wired Broadband Communication Cable Head-End Systems Power Amplifier Linearization Communications Test Equipment TYPICAL APPLICATION 2.5V VDD REFH REFL FLEXIBLE REFERENCE 0.5V TO 2.625V OVDD D9 • • • D0 85 80 75 ANALOG INPUT CORRECTION LOGIC OUTPUT DRIVERS SFDR (dBFS) SFDR vs Input Frequency + INPUT S/H – 10-BIT PIPELINED ADC CORE CMOS OR LVDS 70 65 60 1V RANGE 55 50 45 40 2V RANGE OGND CLOCK/DUTY CYCLE CONTROL 224110 TA01 0 100 200 300 400 500 600 700 800 900 1000 INPUT FREQUENCY (MHz) 224110 G11 ENCODE INPUT 224110fb 1 LTC2241-10 ABSOLUTE MAXIMUM RATINGS OVDD = VDD (Notes 1, 2) Supply Voltage (VDD) ...............................................2.8V Digital Output Ground Voltage (OGND) ........ –0.3V to 1V Analog Input Voltage (Note 3) .......–0.3V to (VDD + 0.3V) Digital Input Voltage......................–0.3V to (VDD + 0.3V) Digital Output Voltage ................ –0.3V to (OVDD + 0.3V) Power Dissipation .............................................1500mW Operating Temperature Range LTC2241C-10 ........................................... 0°C to 70°C LTC2241I-10 ........................................–40°C to 85°C Storage Temperature Range................... –65°C to 150°C PIN CONFIGURATION TOP VIEW 64 GND 63 VDD 62 VDD 61 GND 60 VCM 59 SENSE 58 MODE 57 LVDS 56 OF+/OFA 55 OF–/DA9 54 D9+/DA8 53 D9–/DA7 52 D8+/DA6 51 D8–/DA5 50 OGND 49 OVDD AIN+ 1 AIN+ 2 AIN– 3 AIN– 4 REFHA 5 REFHA 6 REFLB 7 REFLB 8 REFHB 9 REFHB 10 REFLA 11 REFLA 12 VDD 13 VDD 14 VDD 15 GND 16 65 48 D7+/DA4 47 D7–/DA3 46 D6+/DA2 45 D6–/DA1 44 D5+/DA0 43 D5–/DNC 42 OVDD 41 OGND 40 D4+/DNC 39 D4–/CLKOUTA 38 D3+/CLKOUTB 37 D3–/OFB 36 CLKOUT+/DB9 35 CLKOUT–/DB8 34 OVDD 33 OGND UP PACKAGE 64-LEAD (9mm × 9mm) PLASTIC QFN EXPOSED PAD (PIN 65) IS GND, MUST BE SOLDERED TO PCB TJMAX = 150°C, θJA = 20°C/W ORDER INFORMATION LEAD FREE FINISH LTC2241CUP-10#PBF LTC2241IUP-10#PBF LEAD BASED FINISH LTC2241CUP-10 LTC2241IUP-10 TAPE AND REEL LTC2241CUP-10#TRPBF LTC2241IUP-10#TRPBF TAPE AND REEL LTC2241CUP-10#TR LTC2241IUP-10#TR PART MARKING* LTC2241UP-10 LTC2241UP-10 PART MARKING* LTC2241UP-10 LTC2241UP-10 PACKAGE DESCRIPTION 64-Lead (9mm × 9mm) Plastic QFN 64-Lead (9mm × 9mm) Plastic QFN PACKAGE DESCRIPTION 64-Lead (9mm × 9mm) Plastic QFN 64-Lead (9mm × 9mm) Plastic QFN TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *Temperature grades are identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ENC+ 17 ENC– 18 SHDN 19 OE 20 DNC 21 DNC 22 DNC/DB0 23 DNC/DB1 24 OGND 25 OVDD 26 D0–/DB2 27 D0+/DB3 28 D1–/DB4 29 D1+/DB5 30 D2–/DB6 31 D2+/DB7 32 224110fb 2 LTC2241-10 CONVERTER CHARACTERISTICS PARAMETER Resolution (No Missing Codes) Integral Linearity Error Differential Linearity Error Offset Error Gain Error Offset Drift Full-Scale Drift Transition Noise Internal Reference External Reference SENSE = 1V Differential Analog Input (Note 5) Differential Analog Input (Note 6) External Reference The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) CONDITIONS ● ● ● ● ● MIN 10 –0.8 –0.6 –15 –3.5 TYP ±0.3 ±0.15 ±5 ±0.7 ±10 ±60 ±45 0.18 MAX 0.8 0.6 15 3.5 UNITS Bits LSB LSB mV %FS μV/C ppm/C ppm/C LSBRMS ANALOG INPUT The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) SYMBOL VIN VIN, CM IIN ISENSE IMODE ILVDS tAP tJITTER PARAMETER Analog Input Range (AIN+ – AIN–) Analog Input Common Mode (AIN+ + AIN–)/2 Analog Input Leakage Current SENSE Input Leakage MODE Pin Pull-Down Current to GND LVDS Pin Pull-Down Current to GND Sample and Hold Acquisition Delay Time Sample and Hold Acquisition Delay Time Jitter Full Power Bandwidth Figure 8 Test Circuit CONDITIONS 2.375V < VDD < 2.625V (Note 7) Differential Input (Note 7) 0 < AIN+, AIN– < VDD 0V < SENSE < 1V ● ● ● ● MIN 1.2 –1 –1 TYP ±0.5 to ±1 1.25 MAX 1.3 1 1 UNITS V V μA μA μA μA ns fsRMS MHz 7 7 0.4 95 1200 DYNAMIC ACCURACY SYMBOL SNR PARAMETER The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. AIN = –1dBFS. (Note 4) CONDITIONS 10MHz Input 70MHz Input 140MHz Input 240MHz Input SFDR Spurious Free Dynamic Range 2nd or 3rd Harmonic (Note 11) 10MHz Input 70MHz Input 140MHz Input 240MHz Input Spurious Free Dynamic Range 4th Harmonic or Higher (Note 11) 10MHz Input 70MHz Input 140MHz Input 240MHz Input S/(N+D) Signal-to-Noise Plus Distortion Ratio (Note 12) 10MHz Input 70MHz Input 140MHz Input 240MHz Input IMD Intermodulation Distortion fIN1 = 135MHz, fIN2 = 140MHz l l l l MIN 59.6 TYP 60.6 60.5 60.5 60.4 78 MAX UNITS dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dBc 224110fb Signal-to-Noise Ratio (Note 10) 65 74 73 72 85 74 85 85 85 60.5 59 60.4 60.4 60.3 81 3 LTC2241-10 INTERNAL REFERENCE CHARACTERISTICS PARAMETER VCM Output Voltage VCM Output Tempco VCM Line Regulation VCM Output Resistance 2.375V < VDD < 2.625V –1mA < IOUT < 1mA CONDITIONS IOUT = 0 (Note 4) MIN 1.225 TYP 1.25 ±35 3 2 MAX 1.275 UNITS V ppm/°C mV/V Ω DIGITAL INPUTS AND DIGITAL OUTPUTS SYMBOL VID VICM RIN CIN VIH VIL IIN CIN OVDD = 2.5V COZ ISOURCE ISINK VOH VOL OVDD = 1.8V VOH VOL VOD VOS High Level Output Voltage Low Level Output Voltage Differential Output Voltage Output Common Mode Voltage IO = –500μA IO = 500μA Hi-Z Output Capacitance Output Source Current Output Sink Current High Level Output Voltage Low Level Output Voltage OE = High (Note 7) VOUT = 0V VOUT = 2.5V IO = –10μA IO = –500μA IO = 10μA IO = 500μA PARAMETER Differential Input Voltage Common Mode Input Voltage Input Resistance Input Capacitance High Level Input Voltage Low Level Input Voltage Input Current Input Capacitance (Note 7) VDD = 2.5V VDD = 2.5V VIN = 0V to VDD (Note 7) CONDITIONS (Note 7) ENCODE INPUTS (ENC +, ENC –) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) MIN ● ● TYP MAX UNITS V 0.2 1.2 1.5 1.5 4.8 2 2.0 Internally Set Externally Set (Note 7) V V kΩ pF V LOGIC INPUTS (OE, SHDN) ● ● ● 1.7 0.7 –10 3 10 V μA pF LOGIC OUTPUTS (CMOS MODE) 3 37 23 2.495 2.45 0.005 0.07 1.75 0.07 ● ● pF mA mA V V V V V V 454 1.375 mV V LOGIC OUTPUTS (LVDS MODE) 100Ω Differential Load 100Ω Differential Load 247 1.125 350 1.250 224110fb 4 LTC2241-10 POWER REQUIREMENTS SYMBOL VD D PSLEEP PNAP OVDD IVDD IOVDD PDISS OVDD IVDD PDISS PARAMETER Analog Supply Voltage Sleep Mode Power Nap Mode Power Output Supply Voltage Analog Supply Current Output Supply Current Power Dissipation Output Supply Voltage Analog Supply Current Power Dissipation (Note 8) (Note 7) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 9) CONDITIONS (Note 8) SHDN = High, OE = High, No CLK SHDN = High, OE = Low, No CLK (Note 8) ● ● ● ● ● ● ● MIN 2.375 TYP 2.5 1 28 MAX 2.625 UNITS V mW mW LVDS OUTPUT MODE 2.375 2.5 226 58 710 0.5 2.5 226 585 2.625 252 70 805 2.625 252 V mA mA mW V mA mW CMOS OUTPUT MODE TIMING CHARACTERISTICS SYMBOL fS tL tH tAP tOE tD tC PARAMETER Sampling Frequency ENC Low Time (Note 7) ENC High Time (Note 7) Sample-and-Hold Aperture Delay Output Enable Delay ENC to DATA Delay ENC to CLKOUT Delay DATA to CLKOUT Skew Rise Time Fall Time Pipeline Latency CMOS OUTPUT MODE tD tC Pipeline Latency ENC to DATA Delay ENC to CLKOUT Delay DATA to CLKOUT Skew Full Rate CMOS Demuxed Interleaved Demuxed Simultaneous The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) CONDITIONS (Note 8) Duty Cycle Stabilizer Off Duty Cycle Stabilizer On Duty Cycle Stabilizer Off Duty Cycle Stabilizer On ● ● ● ● ● MIN 1 2.26 1.5 2.26 1.5 TYP 2.38 2.38 2.38 2.38 0.4 MAX 210 500 500 500 500 UNITS MHz ns ns ns ns ns (Note 7) (Note 7) (Note 7) (tC – tD) (Note 7) ● ● ● ● 5 1 1 –0.6 1.7 1.7 0 0.5 0.5 5 10 2.8 2.8 0.6 ns ns ns ns ns ns Cycles LVDS OUTPUT MODE (Note 7) (Note 7) (tC – tD) (Note 7) ● ● ● 1 1 –0.6 1.7 1.7 0 5 5 5 and 6 2.8 2.8 0.6 ns ns ns Cycles Cycles Cycles 224110fb 5 LTC2241-10 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All voltage values are with respect to ground with GND and OGND wired together (unless otherwise noted). Note 3: When these pin voltages are taken below GND or above VDD, they will be clamped by internal diodes. This product can handle input currents of greater than 100mA below GND or above VDD without latchup. Note 4: VDD = 2.5V, fSAMPLE = 210MHz, LVDS outputs, differential ENC+/ENC– = 2VP-P sine wave, input range = 2VP-P with differential drive, unless otherwise noted. Note 5: Integral nonlinearity is defined as the deviation of a code from a “best straight line” fit to the transfer curve. The deviation is measured from the center of the quantization band. Note 6: Offset error is the offset voltage measured from –0.5 LSB when the output code flickers between 00 0000 0000 and 11 1111 1111 in 2’s complement output mode. Note 7: Guaranteed by design, not subject to test. Note 8: Recommended operating conditions. Note 9: VDD = 2.5V, fSAMPLE = 210MHz, differential ENC+/ENC– = 2VP-P sine wave, input range = 1VP-P with differential drive, output CLOAD = 5pF . Note 10: SNR minimum and typical values are for LVDS mode. Typical values for CMOS mode are typically 0.2dB lower. Note 11: SFDR minimum values are for LVDS mode. Typical values are for both LVDS and CMOS modes. Note 12: SINAD minimum and typical values are for LVDS mode. Typical values for CMOS mode are typically 0.2dB lower. TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted, Note 4) Integral Nonlinearity 1.0 0.8 0.6 0.4 DNL (LSB) INL (LSB) 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 256 512 OUTPUT CODE 768 1024 224110 G01 Differential Nonlinearity 1.0 0.8 0.6 AMPLITUDE (dB) 1024 224110 G02 8192 Point FFT, fIN = 5MHz, –1dB, 2V Range, LVDS Mode 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 256 512 OUTPUT CODE 768 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G03 224110fb 6 LTC2241-10 TYPICAL PERFORMANCE CHARACTERISTICS 8192 Point FFT, fIN = 70MHz, –1dB, 2V Range, LVDS Mode 0 –10 –20 –30 AMPLITUDE (dB) AMPLITUDE (dB) –40 –50 –60 –70 –80 –90 –100 –110 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G04 (TA = 25°C unless otherwise noted, Note 4) 8192 Point FFT, fIN = 240MHz, –1dB, 2V Range, LVDS Mode 0 –10 –20 –30 AMPLITUDE (dB) –40 –50 –60 –70 –80 –90 –100 –110 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G06 8192 Point FFT, fIN = 140MHz, –1dB, 2V Range, LVDS Mode 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G05 8192 Point FFT, fIN = 500MHz, –1dB, 1V Range, LVDS Mode 0 –10 –20 –30 AMPLITUDE (dB) AMPLITUDE (dB) –40 –50 –60 –70 –80 –90 –100 –110 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G07 8192 Point FFT, fIN = 1GHz, –1dB, 1V Range, LVDS Mode 0 –10 –20 –30 AMPLITUDE (dB) –40 –50 –60 –70 –80 –90 –100 –110 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G08 8192 Point 2-Tone FFT, fIN = 135MHz and 140MHz, –1dB, 2V Range, LVDS Mode 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 0 20 40 60 80 FREQUENCY (MHz) 100 224110 G09 SNR vs Input Frequency, –1dB, LVDS Mode 62 61 2V RANGE 60 SFDR (dBFS) 59 58 57 56 55 0 100 200 300 400 500 600 700 800 900 1000 INPUT FREQUENCY (MHz) 224110 G10 SFDR (HD2 and HD3) vs Input Frequency, –1dB, LVDS Mode 85 80 75 85 SFDR (dBFS) 70 65 60 1V RANGE 55 50 45 40 2V RANGE 65 60 80 75 70 95 90 SFDR (HD4+) vs Input Frequency, –1dB, LVDS Mode 2V RANGE 1V RANGE SNR (dBFS) 1V RANGE 0 100 200 300 400 500 600 700 800 900 1000 INPUT FREQUENCY (MHz) 224110 G11 0 100 200 300 400 500 600 700 800 9001000 INPUT FREQUENCY (MHz) 224110 G12 224110fb 7 LTC2241-10 TYPICAL PERFORMANCE CHARACTERISTICS SFDR and SNR vs Sample Rate, 2V Range, fIN = 30MHz, –1dB, LVDS Mode 95 90 SFDR AND SNR (dBFS) 85 80 75 70 65 60 55 50 0 50 150 200 100 SAMPLE RATE (Msps) 250 224110 G13 (TA = 25°C unless otherwise noted, Note 4) SFDR vs Input Level, fIN = 70MHz, 2V Range 100 90 61.0 60.5 80 SFDR (dBc AND dFBS) 70 60 50 40 30 20 10 0 –50 –40 –20 –30 –10 INPUT LEVEL (dBFS) 0 224110 G14 SNR vs SENSE, fIN = 5MHz, –1dB SFDR dBFS 60.0 SNR (dBFS) dBc 59.5 59.0 58.5 58.0 57.5 0.5 SNR 0.6 0.7 0.8 0.9 1 224110 G15 SENSE PIN (V) IVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB 240 230 220 210 1V RANGE 200 190 180 170 IOVDD (mA) IVDD (mA) 2V RANGE 60 50 40 30 20 10 0 IOVDD vs Sample Rate, 5MHz Sine Wave Input, –1dB LVDS OUTPUTS OVDD = 2.5V CMOS OUTPUTS OVDD = 1.8V 0 50 200 150 SAMPLE RATE (Msps) 100 250 224110 G16 0 50 100 150 200 SAMPLE RATE (Msps) 250 224110 G17 224110fb 8 LTC2241-10 PIN FUNCTIONS (CMOS Mode) AIN+ (Pins 1, 2): Positive Differential Analog Input. AIN – (Pins 3, 4): Negative Differential Analog Input. REFHA (Pins 5, 6): ADC High Reference. Bypass to Pins 7, 8 with 0.1μF ceramic chip capacitor, to Pins 11, 12 with a 2.2μF ceramic capacitor and to ground with 1μF ceramic capacitor. REFLB (Pins 7, 8): ADC Low Reference. Bypass to Pins 5, 6 with 0.1μF ceramic chip capacitor. Do not connect to Pins 11, 12. REFHB (Pins 9, 10): ADC High Reference. Bypass to Pins 11, 12 with 0.1μF ceramic chip capacitor. Do not connect to Pins 5, 6. REFLA (Pins 11, 12): ADC Low Reference. Bypass to Pins 9, 10 with 0.1μF ceramic chip capacitor, to Pins 5, 6 with a 2.2μF ceramic capacitor and to ground with 1μF ceramic capacitor. VDD (Pins 13, 14, 15, 62, 63): 2.5V Supply. Bypass to GND with 0.1μF ceramic chip capacitors. GND (Pins 16, 61, 64): ADC Power Ground. ENC+ (Pin 17): Encode Input. Conversion starts on the positive edge. ENC – (Pin 18): Encode Complement Input. Conversion starts on the negative edge. Bypass to ground with 0.1μF ceramic for single-ended encode signal. SHDN (Pin 19): Shutdown Mode Selection Pin. Connecting SHDN to GND and OE to GND results in normal operation with the outputs enabled. Connecting SHDN to GND and OE to VDD results in normal operation with the outputs at high impedance. Connecting SHDN to VDD and OE to GND results in nap mode with the outputs at high impedance. Connecting SHDN to VDD and OE to VDD results in sleep mode with the outputs at high impedance. OE (Pin 20): Output Enable Pin. Refer to SHDN pin function. DNC (Pins 21, 22, 40, 43): Do not connect these pins. DB0-DB9 (Pins 23, 24, 27, 28, 29, 30, 31, 32, 35, 36): Digital Outputs, B Bus. DB9 is the MSB. At high impedance in full rate CMOS mode. OGND (Pins 25, 33, 41, 50): Output Driver Ground. OVDD (Pins 26, 34, 42, 49): Positive Supply for the Output Drivers. Bypass to ground with 0.1μF ceramic chip capacitor. OFB (Pin 37): Over/Under Flow Output for B Bus. High when an over or under flow has occurred. At high impedance in full rate CMOS mode. CLKOUTB (Pin 38): Data Valid Output for B Bus. In demux mode with interleaved update, latch B bus data on the falling edge of CLKOUTB. In demux mode with simultaneous update, latch B bus data on the rising edge of CLKOUTB. This pin does not become high impedance in full rate CMOS mode. CLKOUTA (Pin 39): Data Valid Output for A Bus. Latch A bus data on the falling edge of CLKOUTA. DA0-DA9 (Pins 44, 45, 46, 47, 48, 51, 52, 53, 54, 55): Digital Outputs, A Bus. DA9 is the MSB. OFA (Pin 56): Over/Under Flow Output for A Bus. High when an over or under flow has occurred. LVDS (Pin 57): Output Mode Selection Pin. Connecting LVDS to 0V selects full rate CMOS mode. Connecting LVDS to 1/3VDD selects demux CMOS mode with simultaneous update. Connecting LVDS to 2/3VDD selects demux CMOS mode with interleaved update. Connecting LVDS to VDD selects LVDS mode. MODE (Pin 58): Output Format and Clock Duty Cycle Stabilizer Selection Pin. Connecting MODE to 0V selects offset binary output format and turns the clock duty cycle stabilizer off. Connecting MODE to 1/3VDD selects offset binary output format and turns the clock duty cycle stabilizer on. Connecting MODE to 2/3VDD selects 2’s complement output format and turns the clock duty cycle stabilizer on. Connecting MODE to VDD selects 2’s complement output format and turns the clock duty cycle stabilizer off. SENSE (Pin 59): Reference Programming Pin. Connecting SENSE to VCM selects the internal reference and a ±0.5V input range. Connecting SENSE to VDD selects the internal reference and a ±1V input range. An external reference greater than 0.5V and less than 1V applied to SENSE selects an input range of ±VSENSE. ±1V is the largest valid input range. VCM (Pin 60): 1.25V Output and Input Common Mode Bias. Bypass to ground with 2.2μF ceramic chip capacitor. GND (Exposed Pad) (Pin 65): ADC Power Ground. The exposed pad on the bottom of the package needs to be soldered to ground. 224110fb 9 LTC2241-10 PIN FUNCTIONS (LVDS Mode) AIN+ (Pins 1, 2): Positive Differential Analog Input. AIN– (Pins 3, 4): Negative Differential Analog Input. REFHA (Pins 5, 6): ADC High Reference. Bypass to Pins 7, 8 with 0.1μF ceramic chip capacitor, to Pins 11, 12 with a 2.2μF ceramic capacitor and to ground with 1μF ceramic capacitor. REFLB (Pins 7, 8): ADC Low Reference. Bypass to Pins 5, 6 with 0.1μF ceramic chip capacitor. Do not connect to Pins 11, 12. REFHB (Pins 9, 10): ADC High Reference. Bypass to Pins 11, 12 with 0.1μF ceramic chip capacitor. Do not connect to Pins 5, 6. REFLA (Pins 11, 12): ADC Low Reference. Bypass to Pins 9, 10 with 0.1μF ceramic chip capacitor, to Pins 5, 6 with a 2.2μF ceramic capacitor and to ground with 1μF ceramic capacitor. VDD (Pins 13, 14, 15, 62, 63): 2.5V Supply. Bypass to GND with 0.1μF ceramic chip capacitors. GND (Pins 16, 61, 64): ADC Power Ground. ENC+ (Pin 17): Encode Input. Conversion starts on the positive edge. ENC– (Pin 18): Encode Complement Input. Conversion starts on the negative edge. Bypass to ground with 0.1μF ceramic for single-ended encode signal. SHDN (Pin 19): Shutdown Mode Selection Pin. Connecting SHDN to GND and OE to GND results in normal operation with the outputs enabled. Connecting SHDN to GND and OE to VDD results in normal operation with the outputs at high impedance. Connecting SHDN to VDD and OE to GND results in nap mode with the outputs at high impedance. Connecting SHDN to VDD and OE to VDD results in sleep mode with the outputs at high impedance. OE (Pin 20): Output Enable Pin. Refer to SHDN pin function. DNC (Pins 21, 22, 23, 24): Do not connect these pins. D0–/D0+ to D9–/D9+ (Pins 27, 28, 29, 30, 31, 32, 37, 38, 39, 40, 43, 44, 45, 46, 47, 48, 51, 52, 53, 54): LVDS Digital Outputs. All LVDS outputs require differential 100Ω termination resistors at the LVDS receiver. D9–/D9+ is the MSB. OGND (Pins 25, 33, 41, 50): Output Driver Ground. OVDD (Pins 26, 34, 42, 49): Positive Supply for the Output Drivers. Bypass to ground with 0.1μF ceramic chip capacitor. CLKOUT–/CLKOUT+ (Pins 35 to 36): LVDS Data Valid Output. Latch data on rising edge of CLKOUT–, falling edge of CLKOUT+. OF–/OF+ (Pins 55 to 56): LVDS Over/Under Flow Output. High when an over or under flow has occurred. LVDS (Pin 57): Output Mode Selection Pin. Connecting LVDS to 0V selects full rate CMOS mode. Connecting LVDS to 1/3VDD selects demux CMOS mode with simultaneous update. Connecting LVDS to 2/3VDD selects demux CMOS mode with interleaved update. Connecting LVDS to VDD selects LVDS mode. MODE (Pin 58): Output Format and Clock Duty Cycle Stabilizer Selection Pin. Connecting MODE to 0V selects offset binary output format and turns the clock duty cycle stabilizer off. Connecting MODE to 1/3VDD selects offset binary output format and turns the clock duty cycle stabilizer on. Connecting MODE to 2/3VDD selects 2’s complement output format and turns the clock duty cycle stabilizer on. Connecting MODE to VDD selects 2’s complement output format and turns the clock duty cycle stabilizer off. SENSE (Pin 59): Reference Programming Pin. Connecting SENSE to VCM selects the internal reference and a ±0.5V input range. Connecting SENSE to VDD selects the internal reference and a ±1V input range. An external reference greater than 0.5V and less than 1V applied to SENSE selects an input range of ±VSENSE. ±1V is the largest valid input range. VCM (Pin 60): 1.25V Output and Input Common Mode Bias. Bypass to ground with 2.2μF ceramic chip capacitor. GND (Exposed Pad) (Pin 65): ADC Power Ground. The exposed pad on the bottom of the package needs to be soldered to ground. 224110fb 10 LTC2241-10 FUNCTIONAL BLOCK DIAGRAM AIN+ INPUT S/H FIRST PIPELINED ADC STAGE SECOND PIPELINED ADC STAGE THIRD PIPELINED ADC STAGE FOURTH PIPELINED ADC STAGE FIFTH PIPELINED ADC STAGE GND VDD AIN– VCM 2.2μF 1.25V REFERENCE RANGE SELECT SHIFT REGISTER AND CORRECTION SENSE REF BUF REFH REFL INTERNAL CLOCK SIGNALS OVDD DIFF REF AMP DIFFERENTIAL INPUT LOW JITTER CLOCK DRIVER CONTROL LOGIC OUTPUT DRIVERS • • • + OF – + D9 – + – + – D0 CLKOUT REFLB REFHA 2.2μF 0.1μF 1μF REFLA REFHB 0.1μF 1μF ENC+ ENC– M0DE LVDS SHDN OE 224110 F01 OGND Figure 1. Functional Block Diagram 224110fb 11 LTC2241-10 TIMING DIAGRAMS LVDS Output Mode Timing All Outputs Are Differential and Have LVDS Levels tAP ANALOG INPUT N tH tL ENC– ENC+ tD D0-D9, OF tC N–5 N–4 N–3 N–2 N–1 N+1 N+2 N+3 N+4 CLKOUT– CLKOUT+ 224110 TD01 Full-Rate CMOS Output Mode Timing All Outputs Are Single-Ended and Have CMOS Levels tAP ANALOG INPUT N tH tL ENC– ENC+ tD DA0-DA9, OFA tC CLKOUTB CLKOUTA N–5 N–4 N–3 N–2 N–1 N+1 N+2 N+3 N+4 DB0-DB9, OFB HIGH IMPEDANCE 224110 TD02 224110fb 12 LTC2241-10 TIMING DIAGRAMS Demultiplexed CMOS Outputs with Interleaved Update All Outputs Are Single-Ended and Have CMOS Levels tAP ANALOG INPUT N tH tL ENC– ENC+ tD DA0-DA9, OFA N–5 tD DB0-DB9, OFB N–6 tC CLKOUTB CLKOUTA 224110 TD03 N+2 N+3 N+1 N+4 N–3 N–1 N–4 tC N–2 Demultiplexed CMOS Outputs with Simultaneous Update All Outputs Are Single-Ended and Have CMOS Levels tAP ANALOG INPUT N tH tL ENC– ENC+ tD DA0-DA9, OFA tD DB0-DB9, OFB tC CLKOUTB CLKOUTA 224110 TD04 N+2 N+3 N+1 N+4 N–6 N–4 N–2 N–5 N–3 N–1 224110fb 13 LTC2241-10 APPLICATIONS INFORMATION DYNAMIC PERFORMANCE Signal-to-Noise Plus Distortion Ratio The signal-to-noise plus distortion ratio [S/(N + D)] is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components at the ADC output. The output is band limited to frequencies above DC to below half the sampling frequency. Signal-to-Noise Ratio The signal-to-noise ratio (SNR) is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components except the first five harmonics and DC. Total Harmonic Distortion Total harmonic distortion is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as: ⎛ THD = 20Log ⎜ ⎝ Full Power Bandwidth The full power bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3dB for a full scale input signal. Aperture Delay Time The time from when a rising ENC+ equals the ENC– voltage to the instant that the input signal is held by the sample and hold circuit. Aperture Delay Jitter The variation in the aperture delay time from conversion to conversion. This random variation will result in noise when sampling an AC input. The signal to noise ratio due to the jitter alone will be: SNRJITTER = –20log (2π • fIN • tJITTER) CONVERTER OPERATION As shown in Figure 1, the LTC2241-10 is a CMOS pipelined multi-step converter. The converter has five pipelined ADC stages; a sampled analog input will result in a digitized value five cycles later (see the Timing Diagram section). For optimal performance the analog inputs should be driven differentially. The encode input is differential for improved common mode noise immunity. The LTC2241-10 has two phases of operation, determined by the state of the differential ENC+/ENC– input pins. For brevity, the text will refer to ENC+ greater than ENC– as ENC high and ENC+ less than ENC– as ENC low. 2fa + fb, 2fb + fa, 2fa – fb and 2fb – fa. The intermodulation distortion is defined as the ratio of the RMS value of either input tone to the RMS value of the largest 3rd order intermodulation product. Spurious Free Dynamic Range (SFDR) Spurious free dynamic range is the peak harmonic or spurious noise that is the largest spectral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of a full scale input signal. ( V2 + V3 + V4 + ...Vn )/ V1⎞⎟⎠ 2 2 2 2 where V1 is the RMS amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the second through nth harmonics. The THD calculated in this data sheet uses all the harmonics up to the fifth. Intermodulation Distortion If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermodulation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency. If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at the sum and difference frequencies of mfa ± nfb, where m and n = 0, 1, 2, 3, etc. The 3rd order intermodulation products are 224110fb 14 LTC2241-10 APPLICATIONS INFORMATION Each pipelined stage shown in Figure 1 contains an ADC, a reconstruction DAC and an interstage residue amplifier. In operation, the ADC quantizes the input to the stage and the quantized value is subtracted from the input by the DAC to produce a residue. The residue is amplified and output by the residue amplifier. Successive stages operate out of phase so that when the odd stages are outputting their residue, the even stages are acquiring that residue and vice versa. When ENC is low, the analog input is sampled differentially directly onto the input sample-and-hold capacitors, inside the “Input S/H” shown in the block diagram. At the instant that ENC transitions from low to high, the sampled input is held. While ENC is high, the held input voltage is buffered by the S/H amplifier which drives the first pipelined ADC stage. The first stage acquires the output of the S/H during this high phase of ENC. When ENC goes back low, the first stage produces its residue which is acquired by the second stage. At the same time, the input S/H goes back to acquiring the analog input. When ENC goes back high, the second stage produces its residue which is acquired by the third stage. An identical process is repeated for the third and fourth stages, resulting in a fourth stage residue that is sent to the fifth stage ADC for final evaluation. Each ADC stage following the first has additional range to accommodate flash and amplifier offset errors. Results from all of the ADC stages are digitally synchronized such that the results can be properly combined in the correction logic before being sent to the output buffer. SAMPLE/HOLD OPERATION AND INPUT DRIVE Sample/Hold Operation Figure 2 shows an equivalent circuit for the LTC2241-10 CMOS differential sample-and-hold. The analog inputs are connected to the sampling capacitors (CSAMPLE) through NMOS transistors. The capacitors shown attached to each input (CPARASITIC) are the summation of all other capacitance associated with each input. During the sample phase when ENC is low, the transistors connect the analog inputs to the sampling capacitors and they charge to, and track the differential input voltage. When ENC transitions from low to high, the sampled input LTC2241-10 VDD 10Ω CPARASITIC 1.8pF RON 14Ω CPARASITIC 1.8pF VDD CSAMPLE 2pF RON 14Ω CSAMPLE 2pF AIN+ VDD 10Ω AIN– 1.5V 6k ENC+ ENC– 6k 1.5V 224110 F02 Figure 2. Equivalent Input Circuit voltage is held on the sampling capacitors. During the hold phase when ENC is high, the sampling capacitors are disconnected from the input and the held voltage is passed to the ADC core for processing. As ENC transitions from high to low, the inputs are reconnected to the sampling capacitors to acquire a new sample. Since the sampling capacitors still hold the previous sample, a charging glitch proportional to the change in voltage between samples will be seen at this time. If the change between the last sample and the new sample is small, the charging glitch seen at the input will be small. If the input change is large, such as the change seen with input frequencies near Nyquist, then a larger charging glitch will be seen. Common Mode Bias For optimal performance the analog inputs should be driven differentially. Each input should swing ±0.5V for the 2V range or ±0.25V for the 1V range, around a common mode voltage of 1.25V. The VCM output pin (Pin 60) may be used to provide the common mode bias level. VCM can be tied directly to the center tap of a transformer to set the DC input level or as a reference level to an op amp differential 224110fb 15 LTC2241-10 APPLICATIONS INFORMATION driver circuit. The VCM pin must be bypassed to ground close to the ADC with a 2.2μF or greater capacitor. Input Drive Impedance As with all high performance, high speed ADCs, the dynamic performance of the LTC2241-10 can be influenced by the input drive circuitry, particularly the second and third harmonics. Source impedance and input reactance can influence SFDR. At the falling edge of ENC, the sample-and-hold circuit will connect the 2pF sampling capacitor to the input pin and start the sampling period. The sampling period ends when ENC rises, holding the sampled input on the sampling capacitor. Ideally the input circuitry should be fast enough to fully charge the sampling capacitor during the sampling period 1/(2fS); however, this is not always possible and the incomplete settling may degrade the SFDR. The sampling glitch has been designed to be as linear as possible to minimize the effects of incomplete settling. For the best performance, it is recommended to have a source impedance of 100Ω or less for each input. The source impedance should be matched for the differential inputs. Poor matching will result in higher even order harmonics, especially the second. Input Drive Circuits Figure 3 shows the LTC2241-10 being driven by an RF transformer with a center tapped secondary. The secondary center tap is DC biased with VCM, setting the ADC input signal at its optimum DC level. Terminating on the transformer secondary is desirable, as this provides a common mode path for charging glitches caused by the sample and hold. Figure 3 shows a 1:1 turns ratio transformer. Other turns ratios can be used if the source impedance seen by the ADC does not exceed 100Ω for each ADC input. A disadvantage of using a transformer is the loss of low frequency response. Most small RF transformers have poor performance at frequencies below 1MHz. Figure 4 demonstrates the use of a differential amplifier to convert a single ended input signal into a differential input signal. The advantage of this method is that it provides low frequency input response; however, the limited gain ANALOG INPUT 0.1μF bandwidth of most op amps will limit the SFDR at high input frequencies. Figure 5 shows a capacitively-coupled input circuit. The impedance seen by the analog inputs should be matched. The 25Ω resistors and 12pF capacitor on the analog inputs serve two purposes: isolating the drive circuitry from 10Ω VCM 2.2μF 0.1μF ANALOG INPUT T1 1:1 25Ω 25Ω 25Ω 0.1μF AIN+ AIN+ 12pF 25Ω AIN– AIN– 224110 F03 LTC2241-10 T1 = MA/COM ETC1-1T RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE Figure 3. Single-Ended to Differential Conversion Using a Transformer 50Ω HIGH SPEED DIFFERENTIAL AMPLIFIER VCM 2.2μF 25Ω 3pF AIN+ AIN+ 12pF LTC2241-10 + CM + – – 25Ω 3pF AIN– AIN– 224110 F04 Figure 4. Differential Drive with an Amplifier VCM 100Ω 0.1μF 100Ω 25Ω 2.2μF AIN+ AIN+ ANALOG INPUT 0.1μF 25Ω 12pF AIN– AIN– 224110 F05 LTC2241-10 Figure 5. Capacitively-Coupled Drive 224110fb 16 LTC2241-10 APPLICATIONS INFORMATION the sample-and-hold charging glitches and limiting the wideband noise at the converter input. For input frequencies higher than 100MHz, the capacitor may need to be decreased to prevent excessive signal loss. The AIN+ and AIN– inputs each have two pins to reduce package inductance. The two AIN+ and the two AIN– pins should be shorted together. For input frequencies above 100MHz the input circuits of Figure 6, 7 and 8 are recommended. The balun transformer gives better high frequency response than a flux coupled center tapped transformer. The coupling capacitors allow the analog inputs to be DC biased at 1.25V. In Figure 8 the series inductors are impedance matching elements that maximize the ADC bandwidth. Reference Operation Figure 9 shows the LTC2241-10 reference circuitry consisting of a 1.25V bandgap reference, a difference amplifier and switching and control circuit. The internal voltage reference can be configured for two pin selectable input ranges of 2V (±1V differential) or 1V (±0.5V differential). Tying the SENSE pin to VDD selects the 2V range; typing the SENSE pin to VCM selects the 1V range. The 1.25V bandgap reference serves two functions: its output provides a DC bias point for setting the common mode voltage of any external input circuitry; additionally, the reference is used with a difference amplifier to generate the differential reference levels needed by the internal ADC circuitry. An external bypass capacitor is required for the 1.25V reference output, VCM. This provides a high frequency low impedance path to ground for internal and external circuitry. The difference amplifier generates the high and low reference for the ADC. High speed switching circuits are connected to these outputs and they must be externally bypassed. Each output has four pins: two each of REFHA and REFHB for the high reference and two each of REFLA and REFLB for the low reference. The multiple output pins are needed to reduce package inductance. Bypass capacitors must be connected as shown in Figure 9. 0.1μF ANALOG INPUT 25Ω T1 0.1μF 25Ω AIN– AIN– T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE 224110 F07 10Ω VCM 2.2μF 0.1μF ANALOG INPUT 25Ω T1 0.1μF 25Ω 12Ω 0.1μF AIN+ AIN+ 8pF AIN– AIN– LTC2241-10 12Ω T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE 224110 F06 Figure 6. Recommended Front End Circuit for Input Frequencies Between 100MHz and 250MHz 10Ω VCM 2.2μF AIN+ 0.1μF AIN+ LTC2241-10 Figure 7. Recommended Front End Circuit for Input Frequencies Between 250MHz and 500MHz 10Ω VCM 2.2μF 0.1μF ANALOG INPUT 25Ω T1 0.1μF 25Ω 2.7nH 0.1μF AIN+ AIN+ AIN– AIN– LTC2241-10 2.7nH T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE 224110 F08 Figure 8. Recommended Front End Circuit for Input Frequencies Above 500MHz 224110fb 17 LTC2241-10 APPLICATIONS INFORMATION LTC2241-10 1.25V VCM 2.2μF 1V RANGE DETECT AND CONTROL SENSE REFLB 0.1μF REFHA BUFFER INTERNAL ADC HIGH REFERENCE 0.5V 2Ω 1.25V BANDGAP REFERENCE the SENSE pin is driven externally, it should be bypassed to ground as close to the device as possible with a 1μF ceramic capacitor. Input Range The input range can be set based on the application. The 2V input range will provide the best signal-to-noise performance while maintaining excellent SFDR. The 1V input range will have better SFDR performance, but the SNR will degrade by 1.7dB. See the Typical Performance Characteristics section. Driving the Encode Inputs The noise performance of the LTC2241-10 can depend on the encode signal quality as much as on the analog input. The ENC+/ENC– inputs are intended to be driven differentially, primarily for noise immunity from common mode noise sources. Each input is biased through a 4.8k resistor to a 1.5V bias. The bias resistors set the DC operating point for transformer coupled drive circuits and can set the logic threshold for single-ended drive circuits. Any noise present on the encode signal will result in additional aperture jitter that will be RMS summed with the inherent ADC aperture jitter. TIE TO VDD FOR 2V RANGE; TIE TO VCM FOR 1V RANGE; RANGE = 2 • VSENSE FOR 0.5V < VSENSE < 1V 1μF 2.2μF DIFF AMP 1μF REFLA 0.1μF REFHB INTERNAL ADC LOW REFERENCE 224110 F09 Figure 9. Equivalent Reference Circuit 1.25V 8k 0.75V 12k VCM 2.2μF SENSE 1μF LTC2241-10 In applications where jitter is critical (high input frequencies) take the following into consideration: 224110 F10 1. Differential drive should be used. 2. Use as large an amplitude as possible; if transformer coupled use a higher turns ratio to increase the amplitude. 3. If the ADC is clocked with a sinusoidal signal, filter the encode signal to reduce wideband noise. 4. Balance the capacitance and series resistance at both encode inputs so that any coupled noise will appear at both inputs as common mode noise. The encode inputs have a common mode range of 1.2V to 2.0V. Each input may be driven from ground to VDD for single-ended drive. Figure 10. 1.5V Range ADC Other voltage ranges in between the pin selectable ranges can be programmed with two external resistors as shown in Figure 10. An external reference can be used by applying its output directly or through a resistor divider to SENSE. It is not recommended to drive the SENSE pin with a logic device. The SENSE pin should be tied to the appropriate level as close to the converter as possible. If 224110fb 18 LTC2241-10 APPLICATIONS INFORMATION LTC2241-10 VDD TO INTERNAL ADC CIRCUITS 1.5V BIAS 4.8k ENC+ 50Ω 8.2pF 0.1μF 50Ω ENC– 0.1μF 100Ω VDD 1.5V BIAS 4.8k CLOCK INPUT T1 MA/COM 0.1μF ETC1-1-13 VDD • • 224110 F11 Figure 11. Transformer Driven ENC+/ENC– VTHRESHOLD = 1.5V ENC+ 1.5V ENC– LTC2241-10 0.1μF 224110 F12a 0.1μF LVDS CLOCK ENC+ LTC2241-10 100Ω 0.1μF ENC– 224110 F12b Figure 12a. Single-Ended ENC Drive, Not Recommended for Low Jitter Figure 12b. ENC Drive Using LVDS Maximum and Minimum Encode Rates The maximum encode rate for the LTC2241-10 is 210Msps. For the ADC to operate properly, the encode signal should have a 50% (±5%) duty cycle. Each half cycle must have at least 2.26ns for the ADC internal circuitry to have enough settling time for proper operation. Achieving a precise 50% duty cycle is easy with differential sinusoidal drive using a transformer or using symmetric differential logic such as PECL or LVDS. An optional clock duty cycle stabilizer circuit can be used if the input clock has a non 50% duty cycle. This circuit uses the rising edge of the ENC+ pin to sample the analog input. The falling edge of ENC+ is ignored and the internal falling edge is generated by a phase-locked loop. The input clock duty cycle can vary from 40% to 60% and the clock duty cycle stabilizer will maintain a constant 50% internal duty cycle. If the clock is turned off for a long period of time, the duty cycle stabilizer circuit will require one hundred clock cycles for the PLL to lock onto the input clock. To use the clock duty cycle stabilizer, the MODE pin should be connected to 1/3VDD or 2/3VDD using external resistors. The lower limit of the LTC2241-10 sample rate is determined by droop of the sample-and-hold circuits. The pipelined architecture of this ADC relies on storing analog signals on small valued capacitors. Junction leakage will discharge the capacitors. The specified minimum operating frequency for the LTC2241-10 is 1Msps. DIGITAL OUTPUTS Table 1 shows the relationship between the analog input voltage, the digital data bits, and the overflow bit. 224110fb 19 LTC2241-10 APPLICATIONS INFORMATION Table 1. Output Codes vs Input Voltage AIN+ – AIN– (2V Range) >+1.000000V +0.998047V +0.996094V +0.001953V 0.000000V –0.001953V –0.003906V –0.998047V –1.000000V