TDA8012A Philips Semiconductors, TDA8012A Datasheet - Page 9

• Manufacturer Part Number: TDA8012A
• Description: Low power PLL FM demodulator for satellite TV receivers
• Manufacturer: Philips Semiconductors

Philips Semiconductors
13. For applications in which a fixed AGC threshold is used, it is recommended to use the internal resistor voltage divider
14. In the application circuit (see Fig.4) the voltage at the AGC output decreases when the IF input level increases above
15. The outputs from the AFC and carrier detector are combined at pin 19 (see Fig.3). During search tuning, when the
16. This current discharges the external capacitors between two energy dispersal peak values and avoid the use of
17. The drift of the automatic frequency control voltage is measured in accordance with the following method:
1997 May 26
handbook, full pagewidth
Low power PLL FM demodulator for
satellite TV receivers
for lower AGC threshold spread. In this case, the threshold is set to 57 dB V.
the adjusted AGC threshold.
input frequency is outside the capture range, the combined output (carrier detector function) is at a LOW level
(any voltage below 0.6V
(V
in Fig.3, the voltage at pin 19 is now a function of the centre frequency (AFC function). This information may be read
by a microcontroller via the ADC of the satellite frequency synthesizer (TSA5055) and the I
external resistors in parallel with capacitors.
a) At room temperature (T
b) At T
19
pin 20 must be adjusted to obtain a 1.5 V output at the AFC output (pin 19).
be adjusted to obtain 1.5 V at the AFC output. Then the VCO frequency f
(without input signal). The drift of the automatic frequency control voltage will then be equal to the difference
between the input frequency and f
= 0.8V
amb
CC
= 80 C, due to its temperature drift, the AFC output voltage differs from 1.5 V. The input frequency must
to V
CC
). When the input channel is close to the centre frequency, V
CC
amb
). When the PLL becomes locked, the voltage at pin 19 rises to a HIGH level
= 25 C) the TDA8012AM is driven by a 480 MHz unmodulated signal. The voltage at
V CC
V 19
0.45
0.15
0.8
0.6
0.3
1
0
Fig.3 AFC and carrier detector output.
VCO
.
carrier detect on
500 kHz
f o
9
AFC DATA
frequency
MBH932
VCO
19
is measured in free running mode
falls to the LOW level. As shown
2
C-bus.
TDA8012AM
Product specification