NEC DTE-25G5THS Service Manual page 35

Service Manual CP-785A
5-2 IF
The TDA936x has an alignment free IF PLL demodulator. The fully integrated oscillator is automatically
calibrated, using the 12 Mhz crystal as a frequency reference. The IF frequency is simply set in TV-
Processor by I2C bus.
The AFC information is available via I2C bus from the TV-Processor status bytes. The controlling
software uses this information for tuner frequency tracking ( automatic following ). The AFC windows is
typically 125Khz wide. The minimum frequency step of the tuner is 62.5 Khz.
This AFC function is disabled when a program is tuned using the direct frequency entry or after fine
tuning adjustment. Therefore it is recommended to tune channel with the TV search function ( manual or
Auto setup) or using the direct channel entry to enable the Automatic Frequency Control.
SAW filters
Ref.
K3953M
K9650M
The SAW filter ( SF1 ) has a double Nyquist slope at 38.9 MHz needed for this multistandard
application. The disadvantage of this choice is that a 5.5 MHz trap filter ( Z501 ) is needed to suppress
the residual sound carrier in the video for B/G signals.
Standard Features
B/G - IF filter for video application
- TV IF filter with Nyquist slopes at 38.9 MHz
- Constant group delay
B/G - IF filter for audio application
- TV IF audio filter with two channels
- Channel ( B/G) with one pass band for sound
carriers 33.40 MHz
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