ADC12DJ3200: Flatness specs

Hi Lacey

The variation in amplitude response versus frequency on the EVM is primarily due to reflections between the balun output and ADC input ports.

The balun used on that board has poor output return loss. This combined with the input return loss of the ADC causes reflected energy between the balun outputs and ADC inputs to give a cyclical gain response versus frequency.

The amount of variation seen in your own design can be reduced by any of the following changes:

• Place the balun as close as possible to the ADC inputs (this will also make the ripple versus frequency have a smaller frequency delta between peaks or dips)
• Add a resistive attenuator between the balun and ADC inputs
• Select a different balun with improved output return loss

There may also be some reflection between the signal generator output and the input of the EVM. Adding an RF attenuator at the input to the EVM would help in this case.

I hope this is helpful.

Best regards,

Jim B

Hi Lacey

Here is a plot of the input gain response data taken on 3 units up to 4 GHz input frequency. Negative values are more attenuation, positive values are less attenuation. Some peaking circuitry is included to enhance the response above 3500 MHz, that is why the values increase in that region.

Best regards,

Jim B