On 3/7/2015 4:44 PM, Jerry Stuckle wrote:
On 3/7/2015 1:33 PM, rickman wrote:
On 3/7/2015 11:35 AM, Jerry Stuckle wrote:

Slope ADCs are used because they can more accurately recreate the
waveform. To make it simple - let's see the ADC is sampling at twice
the frequency being sampled, i.e. 10kHz signal and 20kHz sampling rate.
If the sample happens to be at the zero crossing point, your ADC will
show zero volts - IOW, no signal. But a slope detecting ADC will show a
fairly high positive slope on one sample and an equally negative slope
on the next sample. By integrating these, the DAC can closely recreate
the signal because it can estimate the maximum amplitude by the slopes
of the samples. No, it won't be perfect - but it will be a lot closer
than your simple ADC.


I don't enjoy discussing things with you because you have to make
everything personal. But I will explain the fallacy of your argument on
the Nyquist sampling rate concept.

You pick a sampling point for the dual slope, integrating converter that
happens to give valid results. But if you shift the phase by 90° so
that this converter sees positive values half the integrating period and
negative values for the other half, it produces all zero samples as
well. So there is really no difference in the two converters regarding
Nyquist rate sampling. It merely depends on the phasing of the sample
clock to the input signal. It also depends on how you define the
"sample point" of an integrating converter, the start, the end or the
middle of the integration period.

I will finally point out that your use of the term "slope detecting ADC"
is invalid. Google returns exactly 4 hits when this term is entered
with quotes. The name of this converter may have slope in it, but that
is because the circuit generates a slope, not because it is detecting a
slope. Please look up the circuit and use a proper name for it such as
integrating ADC or dual slope ADC. The integrating converter is not at
all sensitive to the slope of the input signal, otherwise it would not
be able to measure a DC signal which has a slope of zero.

I'm only replying so that others are not confused by your misstatements.


As I said - I was using this as an example that even your simple mind
might understand. And I knew you would find some fault with it.

But that's why I tried to make it simple. In real life you use at least
three times the frequency; at that rate you would have sample 120
degrees apart - which always provides more accuracy than your simple
detector.

And you think Google is a valid reference? Try EE texts. Of course,
you'll have to learn a few things to understand them. But I know you'll
just dismiss my updates because you refuse to learn.

You can have the last word.

The last word on what exactly? You have made several statements that
were wrong. When you try to justify your misstatements you make more
misstatements. There is nothing wrong with your example. Your
conclusion is wrong. I'm glad that we can put this to bed.

--

Rick