FM-Demodulator for SAT TV with Switchable Input TDA 6142-5X Preliminary Data Bipolar IC Features ● High input sensitivity results in excellent carrier/noise behaviour ● Reduced noise bandwidth for the prescaler with 480-MHz LC circuit ● Limitation of the prescaler's internal bandwidth to 960 MHz ● Due to the LC circuit improvement stability against oscillations ● Interferences reduced by damping higher frequencies with P-DSO-20-1 LC circuit ● Switch for double SAW filter input integrated. Type Ordering Code Package TDA 6142-5X Q67000-A5173 P-DSO-20-1 (SMD) Amplifier and IF demodulator for satellite applications, consisting of: four-stage limiter amplifier with selection circuit and input selector for two IF-inputs, each with a base stage; divider by 4; video amplifier; AGC regulator; AFC-output with adjustable steepness; polarity reversal of the video signal. Application Used in indoor units. Semiconductor Group 1 04.95 TDA 6142-5X Pin Configuration (top view) P-DSO-20-1 Semiconductor Group 2 TDA 6142-5X Pin Definitions and Functions Pin No. Function 1 Connection for parallel resonance circuit 2 Connection for parallel resonance circuit 3 AGC-control voltage output 4 AGC-threshold adjust 5 Demodulator tank circuit 6 Demodulator tank circuit 7 Ground 8 AFC-preamplifier output 9 AFC-low pass filter and feedback point for AFC-sensitivity setting 10 AFC-output to A/D-converter and AFC-low pass filter 11 Video output 12 Video polarity switch input, positive/negative modulation 13 IF-reference input 1 14 IF-input 1, e.g. ∆f = 27 MHz 15 Reference voltage output 16 IF-input select for IF-input 1 or 2 17 IF-reference input 2 18 IF-input 2, e.g. ∆f = 18 MHz 19 Supply voltage 5 V 20 AGC-low pass filter Semiconductor Group 3 TDA 6142-5X Block Diagram Semiconductor Group 4 TDA 6142-5X Circuit Description The FM modulated satellite IF signal is fed to both low-ohm symmetrical inputs of the limiting amplifier via a SAW filter with two symmetrical outputs and different bandwidths. With an external DC voltage at pin 16 of the IF input selector, an IF-input-signal can be switched through the IFinput 1 or IF-input 2. By high frequency blocking of the limiting amplifier's symmetrical inputs, asymmetrical operation is also possible, but with increased noise. An external selection circuit in the penultimate amplifier stage produces good selectivity of the limiting amplifier and thus provides a better suppression of harmonics. The output signal of the amplifier is fed to a divider, which splits the frequency into four. The signal is then led to a quadrature demodulator, once directly, and once with phase shift produced by an external phase-shifting circuit. The demodulated video signal is amplified and is available at the video output. The polarity of this signal can be inverted by a DC voltage applied from outside to the polarity reversal input. The demodulated video signal is likewise used for AFC regulation. It is fed via a preamplifier to an inverting OP amplifier at which an internal reference voltage is present. Any frequency offset appears as a varying DC voltage, which can in turn be led to an external A/D converter. The AFC S-curve and the amplification of the OPs can be adjusted via an external resistor. The information for the field strength of the FM modulated satellite IF signal is present as DC voltage at both the AGC output and the AGC low pass filter. A pot can be used to change the AGC threshold. The IF stage of the satellite tuner , or a prestage, can be regulated via the AGC output by amplification. Semiconductor Group 5 TDA 6142-5X Absolute Maximum Ratings TA = 0 to 70 °C Parameter Symbol Limit Values min. max. Unit Supply voltage VS 0 6 V Selectivity circuit V1, 2 0 6 V AGC-control voltage output V3 1 13 V AGC-threshold input V4 0.3 2 V Demodulator LC-circuit input V5, 6 – 0.3 3 V AFC-amplifier V8 0 6 V AFC-low pass filter V9 0 5 V AFC-output V10 0 5 V Video output V11 1 5 V Video P/N-switching V12 – 0.3 6 V IF-inputs V13, 14, 17, 18 0.3 3 V Reference voltage V15 0.3 5 V IF-input selector V16 0.3 5 V AGC-low pass filter V20 – 0.3 5 V Junction temperature Tj 150 °C Storage temperature Tstg 125 °C Thermal resistance Rth SA 125 K/W – 40 Operating Range Supply voltage VS 4.5 5.5 V Input frequency range f15 360 560 MHz Ambient temperature during operation TA 0 70 °C Semiconductor Group 6 Test Condition Open collector TDA 6142-5X Characteristics TA = 25 °C; VS = 5 V ± 10 % (test circuit 1) Parameter Power consumption Symbol Limit Values Unit min. typ. max. IS 30 40 50 mA aIFin – 65 3 dBm Test Condition Input Sensitivity IF-input f13, 14 & 17, 18 = 480 MHz IF-Input Switching V16 V16 3.2 0 5 2.8 V V Video voltage (∆f = 13.5 MHz) V11 400 600 mV Distortion factor THD <1 % Signal/noise ratio S/N 70 dB IF-input 1 IF-input 2 Video Output Video P/N-Switching Positive polarity Input current Negative polarity Input current V12 I12 H V12 I12 L 3.5 5 50 1 – 50 0 V µA V µA AGC-Current aIFin = – 28 dBm aIFin = – 18 dBm I3 I3 10 500 µA µA V3 = 8 V; Resistor 2.4 VS V V R2/R1 = 7 R2/R1 = 7 – 0.9 V 0.05 V at Pin 4 = 4.7 kΩ AFC-Voltage (Open-collector current limited) fIFin = 480 MHz fIFin = 440 MHz fIFin = 520 MHz Semiconductor Group V10 V10 V10 7 TDA 6142-5X Test Circuit 1 Semiconductor Group 8 TDA 6142-5X Application Circuit Semiconductor Group 9 TDA 6142-5X Diagram 1 Diagram 2 Semiconductor Group 10