Datasheet
28
48 76 48
b
0
28
48 76
b
1
S
28
48 76
b
2
76
28
76 48
a
1
28
76 48
a
2
M0012-01
z
–1
z
–1
Magnitude
Truncation
z
–1
z
–1
TAS5508C
www.ti.com
SLES257–SEPTEMBER 2010
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), as shown in Figure 2-12. The 76-bit ALU in
the TAS5508C 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 I
2
C interface. See
Table 2-3.
Figure 2-12. Biquad Filter Structure
All five coefficients for one biquad filter structure are written to one I
2
C register containing 20 bytes (or five
32-bit words). The structure is the same for all biquads in the TAS5508C. Registers 0x51–0x88 show all
the biquads in the TAS5508C. Note that u[31:28] bits are unused and default to 0x0.
Table 2-3. Contents of One 20-Byte Biquad Filter Register (Default = All-Pass)
INITIALIZATION GAIN COEFFICIENT VALUE
DESCRIPTION REGISTER FIELD CONTENTS
DECIMAL HEX
b
0
coefficient u[31:28], b0[27:24], b0[23:16], b0[15:8], b0[7:0] 1.0 0x00, 0x80, 0x00, 0x00
b
1
coefficient u[31:28], b1[27:24], b1[23:16], b1[15:8], b1[7:0] 0.0 0x00, 0x00, 0x00, 0x00
b
2
coefficient u[31:28], b2[27:24], b2[23:16], b2[15:8], b2[7:0] 0.0 0x00, 0x00, 0x00, 0x00
a
1
coefficient u[31:28], a1[27:24], a1[23:16], a1[15:8], a1[7:0] 0.0 0x00, 0x00, 0x00, 0x00
a
2
coefficient u[31:28], a2[27:24], a2[23:16], a2[15:8], a2[7:0] 0.0 0x00, 0x00, 0x00, 0x00
2.6 Bass and Treble Controls
From 32-kHz to 96-kHz data, the TAS5508C has four bass and treble tone controls. Each control has a
±18-dB control range with selectable corner frequencies and second-order slopes. These controls operate
four channel groups:
• L, R, and C (channels 1, 2, and 7)
• LS, RS (channels 3 and 4)
• LBS, RBS (alternatively called L and R lineout) (channels 5 and 6)
• Sub (channel 8)
For 176.4-kHz and 192-kHz data, the TAS5508C has two bass and treble tone controls. Each control has
a ±18-dB I
2
C control range with selectable corner frequencies and second-order slopes. These controls
operate two channel groups:
Copyright © 2010, Texas Instruments Incorporated Description 29
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