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.
Type
Ordering Code
Package
TDA 6142-5X
Q67000-A5173
P-DSO-20-1 (SMD)
FM-Demodulator for SAT TV with
Switchable Input
Preliminary Data
Bipolar IC
TDA 6142-5X
P-DSO-20-1
Features
q
High input sensitivity results in excellent carrier/noise
behaviour
q
Reduced noise bandwidth for the prescaler with 480-MHz
LC circuit
q
Limitation of the prescaler's internal bandwidth to 960 MHz
q
Due to the LC circuit improvement stability against
oscillations
q
Interferences reduced by damping higher frequencies with
LC circuit
q
Switch for double SAW filter input integrated.
Semiconductor Group
1
04.95
Semiconductor Group
2
Pin Configuration
(top view)
P-DSO-20-1
TDA 6142-5X
Semiconductor Group
3
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
4
Block Diagram
TDA 6142-5X
Semiconductor Group
5
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 IF-
input 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
6
Absolute Maximum Ratings
T
A
= 0 to 70
C
Parameter
Symbol
Limit Values
Unit
Test Condition
min.
max.
Supply voltage
V
S
0
6
V
Selectivity circuit
V
1, 2
0
6
V
AGC-control voltage output
V
3
1
13
V
Open collector
AGC-threshold input
V
4
0.3
2
V
Demodulator LC-circuit input
V
5, 6
0.3
3
V
AFC-amplifier
V
8
0
6
V
AFC-low pass filter
V
9
0
5
V
AFC-output
V
10
0
5
V
Video output
V
11
1
5
V
Video P/N-switching
V
12
0.3
6
V
IF-inputs
V
13, 14, 17, 18
0.3
3
V
Reference voltage
V
15
0.3
5
V
IF-input selector
V
16
0.3
5
V
AGC-low pass filter
V
20
0.3
5
V
Junction temperature
T
j
150
C
Storage temperature
T
stg
40
125
C
Thermal resistance
R
th SA
125
K/W
Operating Range
Supply voltage
V
S
4.5
5.5
V
Input frequency range
f
15
360
560
MHz
Ambient temperature
during operation
T
A
0
70
C
TDA 6142-5X
Semiconductor Group
7
TDA 6142-5X
Characteristics
T
A
= 25
C;
V
S
= 5 V
10 % (test circuit 1)
Parameter
Symbol
Limit Values
Unit
Test Condition
min.
typ.
max.
Power consumption
I
S
30
40
50
mA
Input Sensitivity
IF-input
a
IFin
65
3
dBm
f
13, 14 & 17, 18
=
480 MHz
IF-Input Switching
IF-input 1
IF-input 2
V
16
V
16
3.2
0
5
2.8
V
V
Video Output
Video voltage
(
f
= 13.5 MHz)
V
11
400
600
mV
Distortion factor
THD
< 1
%
Signal/noise ratio
S/N
70
dB
Video P/N-Switching
Positive polarity
Input current
Negative polarity
Input current
V
12
I
12 H
V
12
I
12 L
3.5
0
5
50
1
50
V
A
V
A
AGC-Current
a
I
Fin
= 28 dBm
a
I
Fin
= 18 dBm
I
3
I
3
10
500
A
A
V
3
= 8 V; Resistor
at Pin 4 = 4.7 k
AFC-Voltage (Open-collector current limited)
f
I
Fin
= 480 MHz
f
I
Fin
= 440 MHz
f
I
Fin
= 520 MHz
V
10
V
10
V
10
2.4
V
S
0.9 V
0.05
V
V
V
R
2
/
R
1
= 7
R
2
/
R
1
= 7
Semiconductor Group
8
Test Circuit 1
TDA 6142-5X
Semiconductor Group
9
TDA 6142-5X
Application Circuit
Semiconductor Group
10
TDA 6142-5X
Diagram 1
Diagram 2
PDF 
ZIP