TDA7513T datasheet(32/84 Pages) STMICROELECTRONICS

32 / 84 page

Functional description

TDA7513T

32/84

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:

tTIM = (IRC + 1) / fOSC

tCNT = (CF + 1697) / fIF (FM mode)

tCNT = (CF + 448) / fIF (AM mode)

where

tTIM = IF timer cycle time (sampling time)

tCNT = IF counter cycle time

Counting succesful:

tCNT - tERR = tTIM = tCNT + tERR

Count failed:

tTIM > tCNT + tERR

tTIM < tCNT - tERR

where

tERR = 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).

3.3.10

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

Audio processor

3.4.1

Input multiplexer

CD quasi differential 1

CD quasi differential 2

Stereodecoder input (for both FM and AM signals).

3.4.2

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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