TAS5706PAPR datasheet(34/62 Pages) TI

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Loudness Function

Volume

Biquad(0x24)

From

Input

Mux

Output

Mux

Loudness

Biquad(0x23)

Gain=G

1ifVol

1/G

0ifVol

1/G+1/Scale

Scale(Vol

1/G)otherwise

0ifVol

1/G

1ifVol

1/G+1/Scale

Scale(Vol

1/G)otherwise

B0273-01

Scale=1/(1

1/G)

TAS5706

SLOS550A – DECEMBER 2007 – REVISED DECEMBER 2007

The TAS5706 provides a direct form I biquad for loudness on the subwoofer channel. The first biquad is

contained in a gain-compensation circuit that maintains the overall system gain at 1 or less to prevent clipping at

loud volume settings. This gain compensation is shown in Figure 46

Figure 46. Biquad Gain Control Structure

Table 1. Loudness Table Example for Gain = 4, 1/G = 0.25, Scale = 1.33

Volume

0.125

0.25

0.375

0.5

0.625

0.75

0.875

1.125

1.25

1.375

1.5

1.625

1.75

1.875

Biquad path

0.833

0.666

0.5

0.333

0.166

Direct path

0.166

0.333

0.5

0.666

0.833

Total gain

The biquads are implemented in a direct form-I architecture. The direct form-I structure provides a separate delay

element and mixer (gain coefficient) for each node in the biquad filter.

The five 26-bit (3.23) coefficients for the biquad are programmable via the I2C interface.

The following steps are involved in using a loudness biquad with the volume compensation feature:

1. Program the biquad with a loudness filter.

2. Program 0x26 (1/G) and 0x28 (scale).

3. Enable volume compensation in register 0x0E.

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