Hi,
The datasheet for ADS5294 p.55 application information states the need for 5Ω - 15Ω resistor in series with each analogue input, prior to the differential input capacitor.
Our design has a 15pF 0402 C0G capacitor across the differential inputs, plus 12pF from each input to ground, with a 383R + 200R voltage divider providing the input signal at 10-40MSps. All these components are within 5mm of the ADC pins; we also have a video amplifier circuit connected by up to 2” of tracking. See attached picture for a schematic.
The application is for sampling video pixels, so each pixel value presented to the ADC will be settled prior to the sample being taken. (For the faster video rates, we'll adjust the component values to increase the bandwidth!) I'd appreciate your thoughts on whether this is a suitable input stage, or whether the series resistor is critical for a low noise design?
Thanks,
Tim.