TDA7513T_07 Datasheet, PDF (32/84 Pages) STMicroelectronics – Single chip FM/AM tuner with stereo decoder and audio processor

Functional description
TDA7513T
3.3.10
If the comparison result is good the IF counter output changes from LOW to HIGH and is
made available outside at the pin #SD (after a NAND operation with the signal strength
evaluation circuit). The following relationships apply:
t_TIM = (IRC + 1) / f_OSC
t_CNT = (CF + 1697) / f_IF (FM mode)
t_CNT = (CF + 448) / f_IF (AM mode)
where
t_TIM = IF timer cycle time (sampling time)
t_CNT = IF counter cycle time
Counting succesful:
t_CNT - t_ERR = t_TIM = t_CNT + t_ERR
Count failed:
t_TIM > t_CNT + t_ERR
t_TIM < t_CNT - t_ERR
where
t_ERR = discrimination window (controlled by the EW registers)
The IF counter can be started only by inlock information from the PLL, and it is enabled by
software (IFENA).
Adjustment of the measurement time and frequency window
The measurement precision is adjustable by controlling the width of the frequency
discrimination window through control registers EW0 to EW2. The center frequency of the
discrimination window is adjustable by the control register CF0 to CF4. The measurement
time per cycle is adjustable by setting the registers IFS0 - IFS2.
3.4
3.4.1
3.4.2
Audio processor
Input multiplexer
CD quasi differential 1
CD quasi differential 2
Stereodecoder input (for both FM and AM signals).
Input stages
The quasi-differential input stages (see Figure 2.) have been designed to cope with some
CD players in the market having a significant high source impedance which affects strongly
the common-mode rejection of "normal" differential input stages. The additional buffer of the
CD input avoids this drawback and offers the full common-mode rejection even with those
CD players. The quasi-differential input can also be used with normal stereo single-ended
output signal sources such as TAPEOUT.
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