LM3361A

LM3361A Low Voltage Power Narrow Band FM IF System August 1989 LM3361A Low Voltage Power Narrow Band FM IF System General Description The LM3361A contains a complete narrow band FM demodulation system operable to less than 2V supply voltage Blocks within the device include an oscillator mixer FM IF limiting amplifier FM demodulator op amp scan control and mute switch The LM3361A is similar to the MC3361 with the following improvements the LM3361A has higher voltage swing both at the op amp and audio outputs It also has lower nominal drain current and a squelch circuit that draws significantly less current than the MC3361 Device pinout functions are identical with some slightly different operating characteristics Features Y Y Y Y Y Y Functions at low supply voltage (less than 2V) Highly sensitive (b3 dB limiting at 2 0 mV input typical) High audio output (increased 6 dB over MC3361) Low drain current (2 8 mA typ VCC e 3 6V) Minimal drain current increase when squelched Low external parts count Block Diagram and Test Circuit TL H 5586 – 1 Order Number LM3661AM or LM3361AN See NS Package Number M16A or N16E C1995 National Semiconductor Corporation TL H 5586 T1-TOKO RMC-2A6597HM CF-MURATA CFU 455E RRD-B30M115 Printed in U S A Absolute Maximum Ratings If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications 12 V 1 Vrms RF Input Voltage (VSl3 6V) b 0 7 to 5 Vp Mute Function (pin 14) Operating Ambient Temperature Range 0 C to a 70 C b 55 C to a 150 C Storage Temperature Range Package Dissipation (Note 1) Power Supply Voltage (VS) 1500 mW Soldering Information Dual-In-Line Package Soldering (10 seconds) Small Outline Package Vapor Phase (60 seconds) Infrared (15 seconds) 260 C 215 C 220 C See AN-450 ‘‘Surface Mounting Methods and Their Effect on Product Reliability’’ for other methods of soldering surface mount devices Parameters Guaranteed By Electrical Testing (Test ckt TA e 25 C VS e 3 6V fO e 10 7 MHz Df e g 3 kHz fMOD e 1 kHz 50X source) Parameter Supply Voltage Range Supply Current Squelch Off Squelch On RF Input for b3 dB Limiting Recovered Audio at Audio Output Audio Out DC Op Amp Gain Op Amp Output DC Op Amp Input Bias Current Scan Voltage Pin 12 high (2V) Pin 12 Low (0V) Mute Switch Impedance Pin 12 e 0V Switch S1 from pos 1 to pos 2 VS IS IS RF Input Audio Output V9 V11 VIN V10 (V10bV11) 1MX V13 V13 DV14 DI14 200 12 40 04 Measure Min 20 Typ 36 28 36 20 350 15 55 07 20 0 34 15 75 05 18 Max 90 50 60 60 Units V mA mA mV mVRMS VDC dB VDC nA VDC VDC X 30 30 Design Parameters Not Tested or Guaranteed Mixer Conversion Gain (Note 2) Mixer Input Resistance Mixer Input Capacitance Detector Output Impedance Squelch Hysterisis Mute Off Impedance (measure pin 14 with pin 12 Squelch Threshold Detector Center Frequency Slope Typ 46 36 22 500 100 10 0 65 0 15 VV kX pF X mV MX VDC V kHz 2V) Note 1 For operation above 25 C ambient temperature the device must be derated based on 150 C maximum junction temperature and a thermal resistance iJA of 80 C W Note 2 Mixer gain is supply dependent and effects overall sensitivity accordingly (See Typical Performance Characteristics) Coils Toko America 1250 Feehanville Drive Mount Prospect IL 60056 (312) 297-0070 Filters Murata 2200 Lake Park Drive Smyrna GA 30080 (404) 436-1300 2 Typical Performance Characteristics (Test Circuits) TL H 5586 – 2 3 4 TL H 5586 – 3 Internal Schematic Applications Information (See Internal Schematic) OSCILLATOR The Colpitts type oscillator is internally biased with a regulated current source which assures proper operation over a wide supply range The collector base and emitter terminals are at pins 4 1 and 2 respectively The crystal which is used in the parallel resonant mode may be replaced with an appropriate inductor if the application does not require the stability of a crystal oscillator In this case the resonant frequency will be determined by the inductor in parallel with the series combination of C1 and C2 tic also increases distortion (see Typical Performance Characteristics) For proper operation the voltage swing on pin 8 should be adequate to drive the upper rank of the multiplier into switching (about 100 mVrms) This voltage level is dependent on the internal 10 pF capacitor and the tank Rp voltage divider network After detection and de-emphasis the audio output at pin 9 is buffered by an emitter follower OP AMP The op amp inverting input (pin 10) which is internally referenced to 0 7V receives dc bias from the output at pin 11 through the external feedback network Because of the low D C bias maximum swing on the op amp output with 10% distortion is 500 mVrms This can be increased when operating on supplies over 2 3V by adding a resistor from the op amp input to ground which raises the quiescent D C at the output allowing more swing (see figure below for selection of added resistor) The op amp is normally utilized as either a bandpass filter to extract a specific frequency from the audio output such as a ring or dial tone or as a high pass filter to detect noise due to no input at the mixer The latter condition will generate a signal at the op amp output which when applied to pin 12 can mute the external audio amp For max swing VOUT e (VSbVBE) 2 (from internal circuit) so (VSbVBE) 2 e 0 7 1 a therefore R2 e R3 TL H 5586 – 4 so Ct e (C1)(C2) (C1 a C2) and fO e 159 0L(Ct) MIXER The mixer is double balanced to reduce spurious responses The upper pairs are switched by the oscillator while the RF input is applied to the lower pair (pin 16) R43 sets the mixer input impedance at 3 6 kX The mixer output impedance of 1 8 kX will properly match the input impedance of a ceramic filter which is used as a bandpass filter coupling the mixer output to the IF limiting amplifier IF LIMITER The IF amplifier consists of six differential gain stages with the input impedance set by R2 at 1 8 kX to properly terminate the ceramic filter driving the IF The IF alone (without mixer) has a b3 dB limiting sensitivity of approximately 50 mV The system bandwidth is limited to about 5 MHz due to high impedances in the IF which are necessary to meet low power requirements The IF output is connected to the external quad coil at pin 8 via an internal 10 pF capacitor FM DEMOD AUDIO OUT A conventional quadrature detector is used to demodulate the FM signal The Q of the quad coil which is determined by the external resistor placed across it has multiple effects on the audio output Increasing the Q increases output level but because of nonlinearities in the tank phase characteris-  VSbVBE b1 14  R2 R3 J J TL H 5586 – 5 Increasing OP Amp Swing SQUELCH TRIGGER CIRCUIT The squelch trigger circuit is configured such that a low bias on the input (pin 12) will force pin 13 high (200 mV below supply) where it can support at least a 1 mA load and pin 14 to be a low impedance typically 15X to ground Connecting pin 14 to a high impedance ground reference point in the audio path between pin 9 and the audio amp will mute the audio output Pulling pin 12 above mute threshold (0 65V) will force pin 13 to an impedance of about 60 kX to ground and pin 14 will be an open circuit There is 100 mV of hysterisis at pin 12 which effectively prevents jitter 5 LM3361A Low Voltage Power Narrow Band FM IF System Physical Dimensions inches (millimeters) Molded Small Outline Package (M) Order Number LM3361AM NS Package Number M16A Molded Dual-In-Line Package (N) Order Number LM3361AN NS Package Number N16E LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which (a) are intended for surgical implant into the body or (b) support or sustain life and whose failure to perform when properly used in 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