TDA7546 Datasheet, PDF (24/68 Pages) STMicroelectronics – Multichip module for TMC tuner applications

Functional description
TDA7546
IF counter block
The aim of IF counter is to measure the intermediate frequency of the tuner. The input signal
is the 10.7MHz IF level after limiter.
The grade of integration is adjustable by eight different measuring cycle times. The
tolerance of the accepted count value is adjustable, to reach an optimum compromise for
search speed and precision of the evaluation.
Sampling timer
A sampling timer generates the gate signal for the main counter. The basically sampling
time are in FM mode 6.25KHz (t_TIM=160μs).
This is followed by an asynchronous divider to generate several sampling times.
Intermediate frequency main counter
This counter is a 11 - 21-bit synchronous autoreload down counter. Five bits (CF) are
programmable to have the possibility for an adjust to the centre frequency of the IF-filter.
The counter length is automatic adjusted to the chosen sampling time.
At the start the counter will be loaded with a defined value which is an equivalent to the
divider value (t_Sample x f_IF).
If a correct frequency is applied to the IF counter frequency input at the end of the sampling
time the main counter is changing its state from 0h to 1FFFFFh.
This is detected by a control logic and an external search stop output is changing from LOW
to HIGH. The frequency range inside which a successful count result is adjustable by the
EW bits.
CNT = -C----F-----+-----1----6---9---6--
f_IF
Counter result succeeded:
t_TIM ≥ t_CNT - t_ERR
t_TIM ≤ t_CNT + t_ERR
Counter result failed:
t_TIM > t_CNT + t_ERR
t_TIM < t_CNT - t_ERR
t_TIM = IF timer cycle time (sampling time)
t_CNT = IF counter cycle time
t_ERR = discrimination window (controlled by the EW registers)
The IF counter is only started by inlock information from the PLL part. It is enabled by
software (IFENA).
Adjustment of the measurement sequence time
The precision of the measurements is adjustable by controlling the discrimination window.
This is adjustable by programming the control registers EW.
The measurement time per cycle is adjustable by setting the registers IFS.
Adjust of the frequency value
The center frequency of the discrimination window is adjustable by the control registers CF.
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