CS42324 datasheet(34/71 Pages) CIRRUS

34 / 71 page

DS721A6

CS42324

4.3.3

High-Pass Filter and DC Offset Calibration

When using operational amplifiers in the input circuitry driving the CS42324, a small DC offset may be

driven into the A/D converter. The CS42324 includes a high-pass filter after the decimator to remove any

DC offset which could result in recording a DC level, possibly yielding clicks when switching between de-

vices in a multichannel system.

The high-pass filter continuously subtracts a measure of the DC offset from the output of the decimation

filter. If the HPFFreeze bit is set during normal operation, the current value of the DC offset for the each

channel is frozen and this DC offset will continue to be subtracted from the conversion result. This feature

makes it possible to perform a system DC offset calibration by:

Running the CS42324 with the high-pass filter enabled until the filter settles. See “ADC Digital Filter

Characteristics” on page 19 for filter settling time.

Disabling the high-pass filter and freezing the stored DC offset for continuous subtraction.

A system calibration performed in this way eliminates offsets anywhere in the signal path between the

calibration point and the CS42324.

4.3.4

Digital Attenuation Control

Digital attenuation control functions are implemented, offering independent channel control for the ADC

PCM signal path. The volume controls are programmable to ramp in increments of 0.5 dB at a rate con-

trolled by the ADC soft ramp.

Each ADC signal path may also be independently muted via mute control bits. When enabled, each bit

attenuates the signal to its maximum value. When the mute bit is disabled, the signal returns to the atten-

uation level set in the respective volume control register. The attenuation is ramped up and down at the

rate specified by the ADC_SOFT.

4.4

Digital-to-Analog Data Path

4.4.1

Digital Volume Control

Two stereo digital volume control functions are implemented, offering independent channel control for

DAC1 and DAC2 PCM signal paths into the digital mixer. The volume controls are programmable to ramp

in increments of 0.5 dB at a rate controlled by the DAC1/2 soft ramp/zero cross settings.

Each DAC1/2 signal path may also be independently muted via mute control bits. When enabled, each

bit attenuates the signal to its maximum value. When the mute bit is disabled, the signal returns to the

attenuation level set in the respective volume control register. The attenuation is ramped up and down at

the rate specified by the DAC1/2_SOFT and DAC1/2_ZC bits.

4.4.2

Mono Channel Mixer

Independent channel mixers for DAC1 and DAC2 may be used to create a mix of the left and right chan-

nels PCM signals. This mix allows the user to produce a MONO signal from a stereo source. The mixer

may also be used to implement a left/right channel swap.

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