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Question asked by joakimosth on Dec 23, 2016
Latest reply on Feb 24, 2017 by Rajeev


I have a question regarding the ADAR7251 full-scale range. It is configured to bypass LNA+PGA+EQ so I expected the input range to be the maximum available in the datasheet to 5.6Vpp. However, it seems about 1.5-2Vpp is maximum before the ADC start to clip the signal.

Because the clipping voltage is about the same value as the ADC reference (internal) I suspect this are related?

My questions are:

1a. What is the maximum input range to the ADC with LNA+PGA+EQ bypassed.

1b. Is the maximum range also related to the ADC reference voltage?

1c. Is the input signal scaled by some factor before it reach the internal ADC block?

2. What is the accuracy of the ADC? I assume resolution is X Vpp / (2^16 - 1), where X is the maxium input range according to datasheet.


Some observations:

When the input signal (sin-wave) increase in amplitude, the DC-level of the waveform measured at input pin to ADC moves down with increasing amplitude. At some point, close to the ADC reference level the signal jumps to have a DC-level around zero. This jump happens far before the maximum input range as I expect to 5.6Vpp according to datasheet.


Best regards