E-TDA7461ND View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'E-TDA7461ND' PDF : 48 Pages View PDF
Stereo decoder part
TDA7461
4.5.6
4.5.7
Fieldstrength control
The fieldstrength input is used to control the high cut and the stereo blend function. In
addition the signal can be also used to control the noise blanker thresholds.
Level input and gain
To suppress undesired high frequency modulation on the high cut and stereo blend function
the LEVEL signal is lowpass filtered firstly. The filter is a combination of a 1st order RC
lowpass at 53 kHz (working as anti-aliasing filter) and a 1storder switched capacitor lowpass
at 2.2 kHz. The second stage is a programmable gain stage to adapt the LEVEL signal
internally to different IF.
The gain is widely programmable in 16 steps from 0 dB to 10 dB (step = 0.67 dB). These 4
bits are located together with the Roll-Off bits in the “Stereo decoder Adjustment” byte to
simplify a possible adaptation during the production of the carradio.
Figure 22. Internal stereo blend characteristics
4.5.8
Stereo blend control
The stereo blend control block converts the internal LEVEL voltage (LEVEL INTERN) 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 to
be 33%, 42%, 50% or 58% of REF5V (see Figure 23).
To adjust the external LEVEL voltage to the internal range two values must be defined: the
LEVEL gain LG and VSBL. To adjust the voltage where the full channel separation is
reached (VST) the LEVEL gain LG has to be defined. The following equation can be used to
estimate the gain:
LG = F-----i-e----l--d-----s----t--r--e----n---g----t--hR-----E-v---oF----l5--t--aV---g----e----[--S-----T----E----R-----E----O-----]
The gain can be programmed through 4 bits in the "Stereo decoder-Adjustment" byte.
The MONO voltage VMO (0 dB channel separation) can be chosen selecting 33, 42, 50 or
58 % of REF5V.
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