TDA7405 datasheet(33/56 Pages) STMICROELECTRONICS

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TDA7405

4.8 Stereoblend Control

The stereoblend 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. Inter-

nally 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 28, Figure 29).

To adjust the external LEVEL-voltage to the internal range two values must be defined: the LEVEL gain LG and

VSBL (see Figure 29). 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 28. Internal stereoblend characteristics

The gain can be programmed through 4 bits in the "Stereodecoder-Adjustment"-byte. All necessary internal ref-

erence voltages like REF5V are derived from a bandgap circuit. Therefore they have a temperature coefficient

near zero.

Figure 29. Relation between internal and external LEVEL-voltages for setup of Stereoblend

4.9 Highcut Control

The highcut control setup is similar to the stereoblend control setup : 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 30).

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