TDA7513T datasheet(33/84 Pages) STMICROELECTRONICS

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TDA7513T

Functional description

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3.4.3

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.

3.4.4

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.

3.4.5

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.

3.4.6

BASS

There are four parameters programmable in the bass filter stage: (see

Figure 5, 6, 7, and 8):

3.4.7

Attenuation

Figure 5 shows the attenuation as a function of frequency at a center frequency at a center

frequency of 80Hz.

3.4.8

Center frequency

Figure 6 shows the four possible center frequencies: 60,70,80 and 100Hz.

3.4.9

Quality factors

Figure 7 shows the four possible quality factors: 1, 1.25, 1.5 and 2.

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