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ADC3561: ADC suitable for use with switched capacitor FPAA with 1.5V VCM

Jarrod Eliason
Prodigy 50 points
Part Number: ADC3561
Other Parts Discussed in Thread: THS4551, THS4541

Tool/software:

I am developing a reference design for my employer's field programmable analog array (FPAA) product that utilizes switched capacitor technology.  I am looking for an ADC with an external clock input that can be used to clock the ADC with the same clock as the switched capacitor circuitry in order to minimize the sample clock harmonics.  The ADC3561 initially looked like a good candidate, but it has a smaller VCM (0.95V) and smaller input voltage swing than the FPAA, which has a VCM of 1.5V. 

The FPAA has a differential signal path, so I am looking for a differential input on the ADC.  I would be OK with a sample rate down to 2MSPS, and I can go down to 14-bits, although the 16-bit parts seem to have better noise performance, and of course higher dynamic range.  Does anyone have suggestions for an ADC to use with the FPAA, or perhaps an example of an ADC being used with switched capacitor filters?

  • 0
    TI__Expert 3510 points

    Hello Jarrod! 

    Thank you for posting on TI's E2E forum! 

    An FDA like the THS4551, or the THS4541 could be used to adjust your input signal to fit the ADCs input range while also using the ADC's Vcmout to ensure matched common mode as well. 

    I would also like to mention some recently released devices that could also be considered, we have our ADS92xx family of devices that are very similar to the ADC3561, both in features and specs, as well as competitive in performance. 

    The ADS92xx are:

    • 16 -18 bit SAR ADCs
    • Sampling speeds 5, 10, or 20MSPS options
    • 2x Differential, simultaneous sampling channels
    • 4.09VRef; 2.5V Vcm; ±3.2V FSR

    The ADS92xx devices also have an integrated ADC driver to simplify the signal chain as well as to allow for wider bandwidth applications (without the need to slow down the sampling rate). Please see this application note with more information and an example of this: ADS9218 Power-Optimized Signal Chain Circuit. 

    From what you described in your system these devices have a wider input voltage swing and a higher Vcm, which might be closer to your system needs and could allow for additional room when designing the FDA input circuit. It might even allow it for small gain if any rather than attenuation. The Vcmout of the ADS92xx devices can directly be connected to the FDA as well.

    Please let me know if these devices could fit into your needs as well as how else I could help with your design. 

    Best regards, 

    Yolanda