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Driving ADC (ADS1672) from high impedance source

Mike Zakharevich
Prodigy 20 points
Other Parts Discussed in Thread: ADS1672

Hi,

I have a little problem with driving ADC (ADS1672) from high impedance source of low-frequency differential signal.

This ADC clocking by 10 MHz oscillator and according Fig.22 of datasheet (SBAS402D) effective input impedance is 6.25 kOhm. Fig.40 shows a "Basic Differential Input Signal Interface" with 600 Ohm input impedance presumably. Can I increase input impedance of the Basic Circuit by replacing 392 Ohm resistor to 100 kOhm? Whether there are more preferred schematic approaches, OpAmps, etc.?

 PS: The signal source must be DC-coupled with ADC and frequency range is DC-10 kHz. Sampling rate is about 39kSPS.

PPS: Sry for silly question :) 

  • 0
    TI__Guru**** 180821 points

    Hi Mike,

    If I recall correctly, the ADS1672 needs to be driven from a relatively low impedance input - I don't think you could meet data sheet specs by replacing the 392 ohm resistors with 100K.  We'll dig into this a little for you.

  • 0 in reply to Tom Hendrick
    Prodigy 20 points

    Thanks a lot Tom for your reply!

    The ADC connected to source without any drivers, a recommended small input RC-circuit applied only. I tried to increase input impedance by reducing the clock frequency. It improved situation, but desired sample rate could not be reached.

    I guess I should implement a simple differential buffer with high input impedance and low output impedance. I think an experiment is need.