TDA7402_07 Datasheet, PDF (43/71 Pages) STMicroelectronics – Car radio signal processor

TDA7402
Functional description of stereo decoder
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 L_G 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
6.9
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
INTERNAL
VOLTAGES
REF 5V
SETUP OF VST
LEVEL INTERN
INTERNAL
VOLTAGES
REF 5V
SETUP OF VMO
LEVEL INTERN
VSBL
LEVEL
70%
VSBL
20%
VMO
VST
t
FIELDSTRENGHT VOLTAGE
VMO
D00AU1168
t
VST
FIELDSTRENGHT VOLTAGE
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).
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