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ADA2200 EVALZ Quick Start Guide not working as expected

Question asked by JeffreyGage on Jul 25, 2018
Latest reply on Jul 26, 2018 by brianharrington

I am trying to use the ADA2200 as a synchronous demodulator for LVDT Signal Conditioning. I have purchased the ADA2200 EVALZ kit and am trying to verify its functionality before moving on to a more complicated implementation of the dev board. However, I am having trouble setting up the board and producing an output that makes any sense to me.

I;ve come to the same conclusion to the question asked here, except the application and schematic is slightly different. https://ez.analog.com/thread/101935-ada2200-test-circuit

Either I've messed up the configuration or the board is damaged by ESD or such.

 

My goal is to walk through my interpretation of each step and make sure I have the intended meaning and have not missed anything.

I am referring to the schematic and instructions in the current ADA2200 EVALZ datasheet.

 

Quick-Start Schematic

 

Input: The guide suggests a 6.25 kHz single-ended input to IN+, with IN- tied to VOCM. This accomplishes single-ended operation. The 6.25kHz signal is to be triggered by the RCK signal.

The clock (CLKIN) is run by the 500 kHz crystal.

Output: P11-12 are unfiltered and P7-8 are filtered. An oscilloscope probe is attached to P11.

 

My first problem is that I’m not sure what the expected functionality of the quick start circuit will be. I understand with synchronous demodulation of an AM signal that the amplitude envelope is extracted.

 

Normal AM Demod

 

However, this input is not AM. Since I’m putting in a constant amplitude 0-3.3V sinusoid, I’m thinking that I should get a constant voltage value out that corresponds with the constant 3.3V amplitude. If I increase/decrease the amplitude, the output voltage should increase/decrease accordingly.

 

My Attempt: The outputs don't match my expectations. Here is my current output with my best guess at following the quick-start guide. The ADA2200 EVALZ is booted with default settings.

 

Output after following quick-start guide as closely as possible.

A1 is my single-ended input into P2 (IN+).
A2 is the single-ended output at P11 (OUT+).
D0 at the bottom is RCK.

 

A1 is a 0-3.3V, 6.25kHz waveform burst triggered by RCK. RCK has a frequency of 7.812 kHz. At this point the instruction to input a 6.25 kHz wave and sync to the 7.812 kHz RCK makes no sense, as they aren’t the same frequency and the sinusoid doesn’t trigger evenly.

The output A2 (single ended at P11) currently doesn’t mean much to me either. In addition, changing the input burst to 8 kHz makes a smooth input waveform but the output is similarly undecipherable.

Neither outputs line up with my expectation for a constant output voltage that corresponds with the input amplitude.

 

Do my expectations line up with proper operation of the chip? Am I interpreting the quick-start guide correctly? If I’m way off the mark, then what are proper example inputs and outputs for this scenario?

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