I designed an analog integrated circuit that samples and holdsthen rectifies a signal.
To measure the quality of sample and Hold I consider THD below half of the sampling frequency.
My question is how to measure the quality of the rectified signal? Any help is appreciated.
The quality should be determined related to the intended idealized circuit operation. Rectification isn't a clear specification (in my view, you probably know what it means). If you are able to specify the circuit function, you can also derive an error term, that can be measured.