TDA7407D Datasheet, PDF (19/34 Pages) STMicroelectronics – ADVANCED CAR SIGNAL PROCESSOR

TDA7407D
Figure 22. Relation Between Internal and External LEVEL Voltage and Setup of Stereoblend
INTERNAL
VOLTAGES
REF 5V
VSBL
SETUP OF VST
LEVEL INTERN
INTERNAL
VOLTAGES
REF 5V
LEVEL
VSBL
58%
50%
42%
33%
SETUP OF VMO
LEVEL INTERN
t
t
VMO
VST
VST
FIELDSTRENGHT VOLTAGE
D97AU639
VMO
t(s) Figure 23. High cut Characteristics
duc _LOWPASS
ro ^{) TIME CONSTANT}
P _{t(s 3•τDeemp}
FIELDSTRENGHT VOLTAGE
- ^{ObstoelePteroduc τDeemp}
t(s) ^{sole VHCL}
VHCH FIELDSTRENGHT
c ^{b D97AU640}
du _- ^O _{6.5.6 LEVEL Input and Gain}
Pro _t(s) ^{To suppress undesired high frequency modulation on the highcut and stereoblend function the LEVEL sig-}
nal is lowpass filtered firstly.
te ^c The filter is a combination of a 1st order RC lowpass at 53kHz (working as anti-aliasing filter) and a 1st-
le ^{u order switched capacitor lowpass at 2.2kHz. The second stage is a programmable gain stage to adapt the}
so ^{rod LEVEL signal internally to different IF device (see Testmode section 5 LEVELINTERN).}
The gain is widely programmable in 16 steps from 0dB to 10dB (step = 0.67dB). These 4 bits are located
b P _{together with the Roll-Off bits in the "Stereodecoder Adjustment" byte to simplify a possible adaptation dur-}
O _{te ing the production of the carradio.}
ole ^{6.5.7 Stereoblend Control}
s _{The stereoblend control block converts the internal LEVEL voltage (LEVEL INTERN) into an demodulator}
b_{compatible analog signal which is used to control the channel separation between 0dB and the maximum}
O_{separation. Internally this control range has a fixed upper limit which is the internal reference voltage}
REF5V. The lower limit can be programmed between 29.2% and 58%, of REF5V in 4.167% steps (see
figs. 22, 23). To adjust the external LEVEL voltage to the internal range two values must be defined: the
LEVEL gain LG and VSBL (see fig. 15). 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:
L_G = _F----_i--_e---_l-_d-----_s---_t--_r--_e---_n----_g---_h-^R--_t---^E-_v---_o-^F--_l-_t-⁵-_a---^Vg----_e-----_[-_S----_T----_E----_R----_E----_O-----_]
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