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TMDSSOLARPEXPKIT: Lower half of sinusoid is trimmed

user5845893
Intellectual 690 points

Part Number: TMDSSOLARPEXPKIT

I made hardware changes to inverter stage from TMDSSOLARPEXPKIT so it can work with lower current that is <100mA. I changed some resistors responsible for gain of the op-amps. The changes I made was:

R15, R18, R19,R20 from 20k to 1k 
R10, R9 from 9k to 3.3k

I also change the frequency from 20 to 40kHz. 

After the changes I was able to achieve decent sinusoidal waveform, but the lower half is trimmed. Is this because the ADC resolution is not enough to sense the lower values? Or I should add the offset somewhere?