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INA163: INA163 and ADC, Buffer needed?

Jens Hermann
Prodigy 60 points
Part Number: INA163
Other Parts Discussed in Thread: OPA1632, , PCM4220

Hello,

I want to use the PCM4220 as the ADC. The ADC should be used to gather data from an condensator microphone. Also a turntable should be interfaceable. So the INA163 should be my Microphone Preamp. If I use it with the suggested schematic like in the datasheet, can I directly go to the ADC? Or is the ADC Buffer (OPA1632) still needed? My goal is to archieve best results.

  • 0
    TI__Expert 6250 points
    Hi Jens,
    I think for best performance, you'd want to include the OPA1632 before the PCM4220. Adding the OPA1632 will convert your single-ended output from the INA163 to a differential input to the ADC if you ground the input resistor from Pin 1 of the OPA1632 and connect your INA163 output to the input resistor off pin 8 (see Figure 13 in the OPA1632 datasheet for an example). Since the PCM4220 is a differential input ADC, this will maximize your dynamic range and would eliminate any distortion caused by changing the common-mode voltage at the ADC input. Secondly, the recommended OPA1632 drive circuit adds an additional charge-bucket capacitor to improve settling into the ADC, as well as compensation (the 1nF resistor and 40.2 ohm capacitor) to ensure that the circuit remains stable while driving that capacitive load.
  • 0
    Guru 140200 points
    Hi Jens,

    I agree with Alexander. The INA163 has a settling time of 3.5µs which can even increase with the capacitive load of anti-aliasing filter. This is a bit much. So, an additional buffer might be very useful. And don't forget the anti-aliasing filter.

    As you input the signal of a microphone, I think noise in the buffer isn't so much an issue?

    Kai
  • 0 in reply to kai klaas69
    TI__Genius 11135 points
    Jens

    We haven't heard back from you so we assume this answered your questions. If you need additional help just post another reply below.

    Thanks
    Dennis
  • 0 in reply to Dennis Goeke
    Prodigy 60 points

    Thank You very much, I will finish the schematic this week. If there are further questions I will ask. But I really have to thank you for your excellent support. One thing, how do I realise the Antialiasing Filter?

    Regards
    Jens

  • 0 in reply to Jens Hermann
    Guru 140200 points
    Hi Jens,

    it's just what figure 45 of your original post shows. Read again page 24 and 25 of datasheet of PCM4220.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 60 points

    This is just what I have done. I have combined them together as you suggested. I'm just uncertain, which of the values determine the frequency of the low pass filter. Thank You very much. This is what confuses me. For a variable samling rate between 44,1 khz and 96khz it should be 48 khz or not?

    Thank You very much!

    Jens

  • 0 in reply to Jens Hermann
    Guru 140200 points
    Hi Jens,

    one of the characteristics of this PCM4220 is that it provides a heavy oversampling. So, there are no strict requirements for the anti-aliasing filter. Figure 47 of datasheet of PCM4220 shows an active two pole low pass filter with a corner frequency of arround 720kHz.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 60 points
    Okay thus answered my question.I was wondering about thus high frequency.

    Thank You