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STV8203

MULTISTANDARD TV SOUND DEMODULATOR

STMicroelectronics 

STV8203

FUNCTIONAL DESCRIPTION

As can be seen from the block diagram, the input to

the demodulator section is selectable from one of

two I.F. sources via the I2C bus. The selected signal

is then passed through an AGC block, having a

range of 28dB, before being digitised in the

ADC unit. A single quartz crystal (suggestedvalue :

between 24.712MHzand 27MHz) is used for the all

thedigital processing,includingdemodulation,iden-

tification, control, filtering. This has the advantage

of a singleclock signalsource for the wholeIC which

eliminates problems of multiple clock. The single

clock can be chosen to minimize interference in the

TV IF and RF stages of the tuner system.

The demodulatorsystem can identify and demodu-

late all the standarddescribedin the Table1. There-

sult of the recognition is flagged up to the host

system via the I2C bus communication system.

In the case of NICAM transmissions, in the event

of a failure of the received signal or a degradation

of the bit error rate (BER) below a prescribed level,

the system will automaticallydefault to the reserve

sound transmission on mono FM or AM.

For FM demodulation, the discriminator can nor-

mallyhandle signals having 250kHz deviation.This

covers all European standards, and ensure an

optimized compromise for the signal to noise ratio

in one hand, and overmodulation in the other hand.

However, it is possible to extand the deviation

range up to 500kHz (I2C programmable) in order to

cover requests of some broadcasters.

Fully automatic standard recognition and setting

can be achieve using simple routines.

Appropriate de-emphasis networks in the digital

domain are applied to the resulting demodulated

signals (50µs, J17), followed by dematrixing if re-

quired. The digital datastream is then passed

through 2 x 16bits DACs before the audio matrix.

All this first section is working at 3.3V thanks to an

integrated voltage regulator. In stand-by mode, the

voltage regulator pulls the voltage down to zero,

ensuring no power dissipation in this part.

An audio matrix allows the selection of inputs ap-

plied on the outputsSCART1, SCART2 and MONO

according to the diagram shown in Figure 1.

The ”MOUT” outputs either the signal L1, or R1 or

(L1+R1)/2. This allows to record the selected chan-

nel in mono mode, for example on the linear chan-

nel of a VCR simultanously with the stereo mode.

Maximum output swing is 1VRMS.

The audio matrix section has its own power supply

regulator, allowing to keep this part working even

when the rest is in stand-by mode. This achieves a

”THRU” mode from input ”SCART1” to output

”SCART2” andinput”SCART2” to output”SCART1”.

The maximum output swing of both SCART1 and

SCART2 is 2VRMS.

Remark : Circuit operation is possible with only a

single 5V supply. In this case, the AVCC supply pin

is connected to 5V. Maximum output swing is then

limited to 1VRMS and a 6dB attenuationis automat-

ically added to the DAC output. In that case, the

resistor shown as R2 = 39Ω in the ApplicationDia-

gram (between Pin 8 and Pin 21) must be replace

by a short circuit to avoid clipping.

Figure 1 : Audio Matrix

2

DAC

2

LI2(SCART2)

MIN

2

LI1(SCART1)

MUTE

GAIN

± 6dB

MUTE L1/R1

S1

S2

L2/R2

MUTE

2

L1, R1,

(L1 + R1)/2

SELECTOR

2

AO1(SCART1)

MOUT

AO2(SCART2)

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