TLC320AD81C Datasheet, PDF (19/47 Pages) Texas Instruments – Stereo Audio Digital Equalizer DC

2.9 Filter Processor
2.9.1 Biquad Block
The biquad block consists of multiple digital biquad filters per channel organized in a cascade structure as
shown in Figure 2–5. Each of these biquad filters has five downloadable 24-bit (4.20) coefficients. Each
stereo channel has independent coefficients.
Biquad 1
Biquad 2
Biquad N
Figure 2–5. Biquad Cascade Configuration
2.9.2 Filter Coefficients
The filter coefficients for the TLC320AD81C are downloaded through the I²C port and loaded into the biquad
memory space. Digital audio data coming into the device is processed by the biquad block and then
converted into analog waveforms by the DAC. Any biquad filter may be downloaded and processed by the
TLC320AD81C. The biquad structure that is used for the parametric equalization filters is as follows:
+ ^{)) ))} H(z)
b₀
a₀
b₁z–¹
a₁z–¹
b₂z–²
a₂z–²
NOTE: a0 is fixed at value 1 and is not downloadable
The coefficients for these filters are quantized and represented in 4.20 format – 4 bits for the integer part
and 20 bits for the fractional part. In order to transmit them over I²C, it is necessary to separate each
coefficient into three bytes. The first nibble of byte 2 is the integer part, and the second nibble of byte 2 and
bytes 1 and 0 are the fractional parts.
2–7