The TLV320AIC3104-Q1 includes a stereo audio ADC, which uses a delta-sigma modulator with 128-times oversampling in single-rate mode, followed by a digital decimation filter. The ADC supports sampling rates from 8 kHz to 48 kHz in single-rate mode, and up to 96 kHz in dual-rate mode. Whenever the ADC or DAC is in operation, the device requires that an audio master clock be provided and appropriate audio clock generation be set up within the device.

In order to provide optimal system power dissipation, the stereo ADC can be powered one channel at a time, to support the case where only mono record capability is required. In addition, both channels can be fully powered or entirely powered down.

The integrated digital decimation filter removes high-frequency content and downsamples the audio data from an initial sampling rate of 128 f_S to the final output sampling rate of fS. The decimation filter provides a linear phase output response with a group delay of 17 / fS. The –3-dB bandwidth of the decimation filter extends to 0.45 f_S and scales with the sample rate (fS). The filter has minimum 75-dB attenuation over the stop band from 0.55 fS to 64 fS. Independent digital high-pass filters are also included with each ADC channel, with a corner frequency that can be independently set.

Because of the oversampling nature of the audio ADC and the integrated digital decimation filtering, requirements for analog antialiasing filtering are very relaxed. The TLV320AIC3104-Q1 integrates a second-order analog antialiasing filter with 20-dB attenuation at 1 MHz. This filter, combined with the digital decimation filter, provides sufficient antialiasing filtering without requiring additional external components.

The ADC is preceded by a programmable gain amplifier (PGA), which allows analog gain control from 0 dB to 59.5 dB in steps of 0.5 dB. The PGA gain changes are implemented with an internal soft-stepping algorithm that only changes the actual volume level by one 0.5-dB step every one or two ADC output samples, depending on the register programming (see page 0, registers 19 and 22). This soft-stepping ensures that volume control changes occur smoothly with no audible artifacts. On reset, the PGA gain defaults to a mute condition, and on power down, the PGA soft-steps the volume to mute before shutting down. A read-only flag is set whenever the gain applied by PGA equals the desired value set by the register. The soft-stepping control can also be disabled by programming a register bit. When soft stepping is enabled, the audio master clock must be applied to the part after the ADC power-down register is written to ensure the soft-stepping to mute has completed. When the ADC power-down flag is no longer set, the audio master clock can be shut down.