TDA7402 datasheet(43/71 Pages) STMICROELECTRONICS

43 / 71 page

TDA7402

Functional description of stereo decoder

43/71

6.8

Stereo blend control

The stereo blend control block converts the internal LEVEL voltage (LEVELSB) into an

demodulator compatible analog signal which is used to control the channel separation

between 0dB and the maximum separation. Internally this control range has a fixed upper

limit which is the internal reference voltage REF5V. The lower limit can be programmed

between 20 and 70% of REF5V in 3.3% steps (see

Figure 31 and 32).

To adjust the external LEVEL voltage to the internal range two values must be defined: the

LEVEL gain LG and VSBL (see Figure 32). At the point of full channel separation the

external level signal has to be amplified that internally it becomes equal to REF5V. The

second point (e.g. 10dB channel sep.) is then adjusted with the VSBL voltage.

Figure 31.

Internal stereo blend characteristics

The gain can be programmed through 4 bits in the "Stereo decoder adjustment" byte. All

necessary internal reference voltages like REF5V are derived from a bandgap circuit.

Therefore they have a temperature co-efficient near zero.

Figure 32.

Relation between internal and external LEVEL voltages for setup of

stereo blend

6.9

Highcut control

The highcut control set-up is similar to the stereo blend control set up : the starting point

VHCH can be set with 2 bits to be 42, 50, 58 or 66% of REF5V whereas the range can be

set to be 17, 22, 28 or 33% of VHCH (see

Figure 33).

INTERNAL

VOLTAGES

D00AU1168

VSBL

REF 5V

SETUP OF VST

INTERNAL

VOLTAGES

20%

REF 5V

SETUP OF VMO

LEVEL

LEVEL INTERN

FIELDSTRENGHT VOLTAGE

VST

VMO

LEVEL INTERN

70%

VSBL

VST

VMO

FIELDSTRENGHT VOLTAGE

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