STV8203 Просмотр технического описания (PDF) - STMicroelectronics

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STV8203

MULTISTANDARD TV SOUND DEMODULATOR

STMicroelectronics 

STV8203

PROGRAMMING THE DEVICE (continued)

ZWEITON (Pilot Carrier and Tone Detector Thresholds)

Address

Type

Reset

: 10

: R/W

: 1000 1000

bit 7

bit 6

bit 5

THRESH-SIG

bit 4

bit 3

bit 2

bit 1

THRESH-ST

bit 0

THRESH-SIG

THRESH-ST

: Pilot Carrier Level Threshold

Set the sensitivity for the pilot carrier detector.

: Detected Tone Level Threshold

Set the detection threshold level for stereo and dual mono (bi-lingual) tones.

Power on default values give a detection threshold corresponding to a modulated pilot carrier S/N of 0dB

(700Hz BW) and a S/N of 40dB for the recovered audio.

AGCC (AGC Control for ADC)

Address

Type

Reset

: 11

: R/W

: 0001 0001

bit 7

AGC-CMD

bit 6

0

bit 5

0

bit 4

bit 3

AGC-REF

bit 2

bit 1

bit 0

AGC-CST

AGC-CMD : 1 = manual/forced mode, 0 = automatic mode

Normally set to 0 enabling automatic mode. In the case of system L/L’, due to the presence

of the AM sound carrier, the AGC should be switched off. In this case, a fixed gain value

should be set using the AGCS register (see below).

This bit is controlled by AUTOSTANDARD when this function is activated.

AGC-REF : Defines the clipping level.

Adjust the allowable proportion of samples at the input of the ADC which will be clipped; the

AGC tries to maximise the use of the full scale range of the ADC. The default setting gives

a ratio of 1/256.

AGC-REF [4:2]

000

001

010

011

100

101

110

111

1/16 (single carrier)

1/32

1/64

1/128

1/256

1/512

1/1024

1/2048 (multiple carriers)

Clipping Ratio

AGC-CST : AGC time constant between each step of 1.25dB.

For a 27MHz XTAL => 00 = 1.21ms, 01 = 2.43ms, 10 = 4.85ms, 11 = 9.7ms.

The adjustment is a compromise between settling time and noise immunity.

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