I'm using the ADA2200 to implement a lock-in amplifier function. There for I provide the Rclk signal of it to a pll (phase locked loop) and get a sine wave of the same frequency. This signal is then used for excitation, or in my case I just amplifier it and provided to the input of the ADA2200. So the amplitude and phase shift between Rclk and signal input is constant. The output is a analog, diskret wave, just like expected. The Signal is than routed to a SAR ADC, without low pass filtering. The ADC is programmed to sample when the synco signal is high but only when at first Rclk is going high. I do this to allways get samples on the same time.
I then calculate the average of the sampled data. I sample I and Q data to calculate the magnitude of the two signals.
My question is:
1) Is this correct or do I need a low pass filter? I thought that averaging the data would be sufficient, isn't it?
2) What puzzles me is how can I conclusion from this value (averaged output signal) to the amplitude of the input signal? (That is my main concern)
I read the "Theory of operation" and the "Amplitude Measurement" sections in the datasheet but there are still questions.
E.g. the Vcyclemean is given as:
VCYCLEMEAN = Conversion Gain × VIN(RMS) × sin(θREL − θDEL) =1.05 ×VIN(RMS) × sin(θREL − θDEL)
3) But how can I get the θDEL information when I'm not measure a zero cyclemean?
4) How is the relationship between the Vcyclemean and the Amplitude of the input signal?
5) What is the "offset corrected cyclemean" ? Do I have just to subtract the Offset (Vss/2)
6) Should I sample OUTP AND OUTN to get the information about the input signal amplitude or is this the case if the input signal itself is a differential signal?
I don't understand the behaver as well. If there is no input signal, the OUTP is Vss/2. But when I apply a signal it seems that this offset is going down on the OUTP pin. Is this reaction ok?
Thank you for your help.