AD1835A: DC offset voltage

Q I am using the Analog Devices EZ-kit lite 21369 development board which has an AD1835A codec. The problem is that there seems to be an unwanted DC offset on the output values from the ADC's in the codec. I therefore wanted to use the built-in high pass DC blocking filter in the AD1835A. As I understand it from the datasheet of the AD1835A, the filter is enabled by setting bit 8 of the ADC Control 1 register. However, when I set this bit, I still get a DC component on the output of the ADC. Do you have any suggestions to a solution? A The bias voltage that you are seeing on the DACx output pins is normal and will not be removed by register control. An identical voltage is available on the FILTR pin (18), also called Vref and Vbias in various places in the Datasheet. I apologize for the naming confusion. I would recommend that you provide 10uF/0.1uF filtering on the FILTR pin and use this voltage as reference for your DAC output filter stage, as shown in Figure 19 of the Datasheet.

AD1835: Output filters

Q I have a little question about your audio codec AD1835. There are schematics of a typical ADC input antialiasing filter and a DAC output reconstruction filter in the datasheet for AD1835. But there are no comments about parameters of these filters. So I had been simulated them and I found out that critical frequency (fc at -3dB) of ADC filter is about 200kHz and critical frequency of DAC filter is 100kHz. I don't understand why these filters have so high critical frequencies. I think that if samplling freq. is for example 96kHz than maximum frequency component in input signal must be 96kHz / 2 = 48kHz in order that no aliasing arise. The same situation is about output reconstruction filter. Can you explain me why these filters have so high critical frequencies? Wouldn't it be better if these frequencies will be about 40kHz for both ADC and DAC filter? A The filters uses for sigma-delta codecs don't need tight cutoff frequencies. There main aim is to have good attenuation at the frequency the modulators run at, 3MHz in the case of the AD1835. We selected values which give the cutoff at 100KHz so we could operate the parts at sample rates up to 192khz if required. We have also tested these parts with simple RC filters (51ohm and 2.2nF) with no degradation in performance.

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AD1835 Obsolete
For information on this 2 ADC, 8 DAC, 96 kHz, 24-Bit Sigma Delta Codec, please visit the AD1835A product page.
Datasheet
AD1835 on Analog.com

AD1835A Not Recommended for New Designs
The AD1835A is a high-performance single-chip CODEC featuring four stereo DACs and one stereo ADC. Each DAC comprises a high-performance digital interpolation...
Datasheet
AD1835A on Analog.com