TDA8012AM Datasheet, PDF (9/16 Pages) NXP Semiconductors – Low power PLL FM demodulator for satellite TV receivers

Philips Semiconductors
Low power PLL FM demodulator for
satellite TV receivers
Product specification
TDA8012AM
13. For applications in which a fixed AGC threshold is used, it is recommended to use the internal resistor voltage divider
for lower AGC threshold spread. In this case, the threshold is set to 57 dBµV.
14. In the application circuit (see Fig.4) the voltage at the AGC output decreases when the IF input level increases above
the adjusted AGC threshold.
15. The outputs from the AFC and carrier detector are combined at pin 19 (see Fig.3). During search tuning, when the
input frequency is outside the capture range, the combined output (carrier detector function) is at a LOW level
(any voltage below 0.6V_CC). When the PLL becomes locked, the voltage at pin 19 rises to a HIGH level
(V₁₉ = 0.8V_CC to V_CC). When the input channel is close to the centre frequency, V₁₉ falls to the LOW level. As shown
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 I²C-bus.
16. This current discharges the external capacitors between two energy dispersal peak values and avoid the use of
external resistors in parallel with capacitors.
17. The drift of the automatic frequency control voltage is measured in accordance with the following method:
a) At room temperature (T_amb = 25 °C) the TDA8012AM is driven by a 480 MHz unmodulated signal. The voltage at
pin 20 must be adjusted to obtain a 1.5 V output at the AFC output (pin 19).
b) At T_amb = 80 °C, due to its temperature drift, the AFC output voltage differs from 1.5 V. The input frequency must
be adjusted to obtain 1.5 V at the AFC output. Then the VCO frequency f_VCO is measured in free running mode
(without input signal). The drift of the automatic frequency control voltage will then be equal to the difference
between the input frequency and f_VCO.
handbook, full pagewidth
V19
VCC
1
0.8
0.6
0.45
0.3
0.15
0
carrier detect on
MBH932
AFC DATA
fo
500 kHz
frequency
Fig.3 AFC and carrier detector output.
1997 May 26
9