AK4691 Datasheet, PDF(34/80 Page) Asahi Kasei Microsystems – 4ch ADC + 2ch DAC with MIC/HP/SPK-AMP

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AK4691 Datasheet, PDF (34/80 Pages) Asahi Kasei Microsystems – 4ch ADC + 2ch DAC with MIC/HP/SPK-AMP

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[AK4691]

â Digital High Pass Filter

The ADC has a digital high pass filter for DC offset cancellation. The cut-off frequency of the HPF is 1.0Hz (@ fs =

48kHz) and scales with sampling rate (fs). ADC1 and DAC use common HPF. When ADC side is powered-up (PMADC1

bit = â1â or PMADC2 bit = â1â), the HPF of ADC1 is enabled but the HPF of DAC is disabled. When ADC side is

powered-down (PMADC1 = PMADC2 bits = â0â) and DAC is powered-up (PMDAC bit = â1â), the HPF of DAC is

enabled (@ HPFN bit = â0â). When the HPF of DAC is enabled, ON/OFF of the HPF can be selected by HPFN bit. When

changing HPFN bit, DAC should be powered-down. When ADC side is powered-up, HPFN bit must be set to â0â.

PMADC2-1 bits

PMDAC bit HPFN bit

01, 10 or 11

Table 22. HPF ON/OFF (x: Donât care)

HPF

ADC

OFF

DAC

OFF

â Digital EQ/HPF/LPF

The AK4691 has wind-noise reduction filter (FIL1), stereo separation emphasis (FIL3), gain compensation (EQ) and

ALC (Automatic Level Control) in digital domain for A/D converted data (Figure 25). ADC1 and ADC2 have FIL1,

FIL3, and EQ blocks independently. ALC block is common to ADC1 and ADC2. FIL1, FIL3, and EQ blocks are IIR

filters of 1st order. The filter coefficient of FIL3, EQ and FIL1 blocks can be set to any value. Refer to the section of âALC

operationâ about ALC.

When only DAC is powered-up, digital EQ/HPF/LPF circuit in ADC1 operates at playback path. When only ADC is

powered-up or both ADC and DAC are powered-up, digital EQ/HPF/LPF circuit in ADC1 operates at recording path.

Even if the path is switched from recording to playback, the register setting of filter coefficient at recording remains.

Therefore, FIL3A, EQA, FIL1A, GN1A, GN0A bits should be set to â0â if digital EQ/HPF/LPF in ADC1 is not used for

playback path.

When digital EQ/HPF/LPF blocks change from recording path to playback path, ADC1, ADC2 and DAC

(PMADC1=PMADC2=PMDAC bits = â0â) should be powered-down.

MS0672-E-00

- 34 -

2007/11

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