Datasheet

B0155-01

LB1

RB2

Atten

LB2

–

ToLeftChannel

ToRightChannel

TLV320AIC3107

www.ti.com

SLOS545D –NOVEMBER 2008–REVISED DECEMBER 2014

Figure 22. Architecture of the Digital Audio Processing When 3-D Effects are Enabled

It is recommended that the digital effects filters should be disabled while the filter coefficients are being modified.

While new coefficients are being written to the device over the control port, it is possible that a filter using

partially updated coefficients may actually implement an unstable system and lead to oscillation or objectionable

audio output. By disabling the filters, changing the coefficients, and then re-enabling the filters, these types of

effects can be entirely avoided.

10.3.3.3.2 Digital Interpolation Filter

The digital interpolation filter upsamples the output of the digital audio processing block by the required

oversampling ratio before data is provided to the digital delta-sigma modulator and analog reconstruction filter

stages. The filter provides a linear phase output with a group delay of 21/Fs. In addition, programmable digital

interpolation filtering is included to provide enhanced image filtering and reduce signal images caused by the

upsampling process that are below 20 kHz. For example, upsampling an 8-kHz signal produces signal images at

multiples of 8-kHz (i.e., 8 kHz, 16 kHz, 24 kHz, etc.). The images at 8 kHz and 16 kHz are below 20 kHz and still

audible to the listener; therefore, they must be filtered heavily to maintain a good quality output. The interpolation

filter is designed to maintain at least 65 dB rejection of images that land below 7.455 Fs. In order to utilize the

programmable interpolation capability, the Fsref should be programmed to a higher rate (restricted to be in the

range of 39 kHz to 53 kHz when the PLL is in use), and the actual Fs is set using the NDAC divider. For

example, if Fs = 8 kHz is required, then Fsref can be set to 48 kHz, and the DAC Fs set to Fsref/6. This ensures

that all images of the 8-kHz data are sufficiently attenuated well beyond a 20-kHz audible frequency range.

10.3.3.3.3 Delta-Sigma Audio DAC

The stereo audio DAC incorporates a third order multi-bit delta-sigma modulator followed by an analog

reconstruction filter. The DAC provides high-resolution, low-noise performance, using oversampling and noise

shaping techniques. The analog reconstruction filter design consists of a 6-tap analog FIR filter followed by a

continuous time RC filter. The analog FIR operates at a rate of 128 × Fsref (6.144 MHz when Fsref = 48 kHz,

5.6448 MHz when Fsref = 44.1 kHz). Note that the DAC analog performance may be degraded by excessive

clock jitter on the MCLK input. Therefore, care must be taken to keep jitter on this clock to a minimum.

10.3.3.3.4 Audio DAC Digital Volume Control

The audio DAC includes a digital volume control block which implements a programmable digital gain. The

volume level can be varied from 0 dB to –63.5 dB in 0.5 dB steps, in addition to a mute bit, independently for

each channel. The volume level of both channels can also be changed simultaneously by the master volume

control. Gain changes are implemented with a soft-stepping algorithm, which only changes the actual volume by

one step per input sample, either up or down, until the desired volume is reached. The rate of soft-stepping can

be slowed to one step per two input samples through a register bit.

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