The DSO Nano obviously has a very limited bandwidth/sample rate compared to a desktop oscilloscope. Still I think most would agree that it serves us well for a range of practical measurement challenges (not to mention the form factor and cost). Then what if we double the sampling rate, would it really make a difference and is it practical to do so?
Current max sampling frequency for the DSO Nano is 857 kHz (not 1MHz as most people seem to think). The issue here is with the uC running at 72 MHz. Max speed for the ADC clock is stated in the uC datasheet as 14 MHz and the fastest ADC clock we can select (staying within specifications) is then 12 Mhz (= 857 kHz sampling rate). Reducing system clock to 48 MHz would allow for 1 Ms/s, but this would reduce overall performance accordingly and we may run into a number of timing issues. For most practical purposes I would argue that we need at least 10 samples per cycle, so with the current configuration we’re good to about 85 kHz only.
The uC supports a feature referred to as “dual fast interleave mode” which would allow us to double the sampling rate. That is, the two independent ADC cores will overlap one another and so effectively double the conversion rate. In V2 hardware, two GPIO’s pins are connected (PA0 and PA1) to allow for this. According to the uC datasheet however there is no real need for this as it is perfectly capable of sourcing ADC input from the same pin. Using the second pin (PA1) would limit this feature to V2 owners, but I don’t see any obvious reason (besides market differentiation) why we should do so (perhaps others do?). Implementing this in firmware would then increase bandwidth up to about 170 kHz.
Another choice might be to exceed datasheet recommendations and bump the ADC clock up to 18MHz. This should give us 2.57 Ms/s and a usable bandwidth up towards 257 kHz.
So back to the questions, are there any good examples of things we can (and need to measure) at 170k Hz or 257 kHz or are there issues with or alternatives to the above we should consider?