Hi all:
I need some advice on an approach to obtaining 6 adc samples( 10 to 12 bit?) which are time synchronized.
The purpose is to feed a 3 pin semiconductor (BJT, FET etc) an AC, sine wave signal and obtain curve tracer data (volt/current) to profile the unit.The AC means I'll need a virtual ground and do some OPA scaling to feed the ADCs.
I'd like to optimize the number of data points to reasonably track the sine wave feed signal and resultant output etc. I'd like to be able to do the audio spectrum => 20Khz sine wave.
I was looking at this:
https://www.medicine.mcgill.ca/physio/vlab/biomed_signals/atodvlab.htm
It seems I need @ least 40Khz of sampling to meet Nyquist requirements.
If I were to use 10Bit adc, would it be possible to gang 6 ,16F1936's in lockstep and have them do sync'd adc?
Since the input sine wave is repetitive, I believe I can do time shifted sampling.Thus by clocking the sampling based on the perhaps 1/16 period of the signal, after 16 samples I can reconstruct the entire signal (one period) in good detail.
For 16 periods, each cycle of sampling is offset by 1/16 of a period. Thus one sample per period at a cumulative 1/16 period offset. Then by doing this repeatedly I can oversample for better accuracy.
If one complete cycle consumes 16 x 2 = 32 GPR bytes,. Since it's an mcu doing all the sampling I can do a running sum... for each of the 16 sampled points to increase their accuracy. So by doing 64 , (10bit sampling)cycles I can sum the data and get a 10 + 4^3 = 13 bit result, which is quite reasonable,all in 2 byte math.
At a 50 usec period (20khz), sampling should be doable with a 16F1936 @32Mhz, 11usec for a complete sample is possible.
With this method I should be able to overcome the Nyquist limitation.
Then I need to figure out how to send the data for a PC in a format that EXCEL can Parse to do graphes. Any resources around for that?
Once I can get that working, i hope to do DC operating point biasing (and curve tracing) and use small signal inputs to create optimal linear outputs, thereby helping with custom low distortion designs.