TDA7513T_07 Datasheet, PDF (33/84 Pages) STMicroelectronics – Single chip FM/AM tuner with stereo decoder and audio processor

TDA7513T
Functional description
3.4.3
3.4.4
3.4.5
3.4.6
3.4.7
3.4.8
3.4.9
AutoZero
In order to reduce the number of pins there is no AC coupling between the In-Gain and the
following stage, so that in theory any offset generated by or before the In-Gain stage would
be transferred or even amplified to the output. To avoid this undesired situation a special
offset cancellation stage called AutoZero is implemented. This stage is located before the
Volume block to eliminate all offsets generated by the Stereodecoder, the Input Stage and
the In-Gain stage (please note that externally generated offsets, e.g. those generated
because of leakage current into the coupling capacitors, are not cancelled).
The auto-zeroing is started every time the APSD data byte 0 is selected and takes a
maximum time of 0.6ms. The rationale behind this choice is that the APSD byte encodes the
signal source selection, and auto-zero ought to be performed every time a new source is
selected. To avoid audible clicks the audioprocessor is muted before the volume stage
during this time.
AutoZero remain
In some cases, for example if the uP is executing a refresh cycle of the I²C bus
programming, it is not necessary to start a new AutoZero action because no new source is
selected and an undesired mute would appear at the outputs. For such applications the
device can be switched in the "AutoZero Remain mode" (Bit 6 of the APSD subaddress
byte). If this bit is set to high, the APSD data byte 0 can be loaded without invoking the
AutoZero and the old adjustment value remains.
Softmute
The digitally controlled softmute stage allows signal muting and unmuting with a I²C bus
programmable slope. The mute process can either be activated by pin #AUDIOMUTE or I²C
bus. The slope is realized in a special S-shaped curve so as to slowly mute in the critical
regions (see Figure 4.). For timing purposes the Bit 3 of the I²C bus output register is set to
1 from the start of muting until the end of unmuting.
BASS
There are four parameters programmable in the bass filter stage: (see Figure 5, 6, 7, and 8):
Attenuation
Figure 5 shows the attenuation as a function of frequency at a center frequency at a center
frequency of 80Hz.
Center frequency
Figure 6 shows the four possible center frequencies: 60,70,80 and 100Hz.
Quality factors
Figure 7 shows the four possible quality factors: 1, 1.25, 1.5 and 2.
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