TAS5518 datasheet(28/103 Pages) TI

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Introduction

SLES115 — August 2004

TAS5518

1.7

Biquad Filters

For 32-kHz to 96-kHz data, the TAS5518 provides 56 biquads across the eight channels (seven per channel)

For 176.4-kHz and 192-kHz data, the TAS5518 has 21 biquads across the three channels (seven per

channel). All of the biquad filters are second order direct form I structure.

The direct form I structure provides a separate delay element and mixer (gain coefficient) for each node in the

biquad filter. Each mixer output is a signed 76-bit product of a signed 48-bit data sample (25.23 format number)

and a signed 28-bit coefficient (5.23 format number). The 76-bit ALU in the TAS5518 allows the 76-bit

resolution to be retained when summing the mixer outputs (filter products).

The five 28-bit coefficients for the each of the 56 biquads are programmable via the I2C interface. See

Table 1−3.

Z−1

∑

Magnitude

Truncation

Z−1

∑

Magnitude

Truncation

Z−1

Figure 1−15. Biquad Filter Structure

All five coefficients for one biquad filter structure are written to one I2C register containing 20 bytes (or five

32-bit words). The structure is the same for all biquads in the TAS5518. Registers 0x51 – 0x88 show all the

biquads in the TAS5518. Note that u(31:28) bits are unused and default to 0x0.

Table 1−3. Contents of One 20-Byte Biquad Filter Register (Default = All-Pass)

DESCRIPTION

INITIALIZATION GAIN COEFFICIENT VALUE

DECIMAL

HEX

bo Coefficient

u(31:28), b0(27:24), b0(23:16), b0(15:8), b0(7:0)

1.0

0x00, 0x80, 0x00, 0x00

b1 Coefficient

u(31:28), b1(27:24), b1(23:16), b1(15:8), b1(7:0)

0.0

0x00, 0x00, 0x00, 0x00

b2 Coefficient

u(31:28), b2(27:24), b2(23:16), b2(15:8), b2(7:0)

0.0

0x00, 0x00, 0x00, 0x00

a1 Coefficient

u(31:28), a1(27:24), a1(23:16), a1(15:8), a1(7:0)

0.0

0x00, 0x00, 0x00, 0x00

a2 Coefficient

u(31:28), a2(27:24), a2(23:16), a2(15:8), a2(7:0)

0.0

0x00, 0x00, 0x00, 0x00

1.8

Bass and Treble Controls

From 32-kHz to 96-kHz data, the TAS5518 has four Bass and Treble tone controls. Each control has a ±18-dB

control range with selectable corner frequencies and 2nd order slopes. These controls operate four channel

groups:

•

L, R & C (Channels 1, 2, and 7)

•

LS, RS (Channels 3 and 4)

•

LBS, RBS (or alternately called L and R Lineout.) (Channels 5 and 6)

•

Sub (Channel 8)

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