Re: What is PWM input with very high resolution?

Spehro Pefhany wrote:
On Thu, 29 May 2008 12:43:37 -0500, "jani" <a.naseem@xxxxxxxxxxxxx>
wrote:


If someone says they are trying to read PWM input with very high
resolution(2 ^ 30), I think they meant 2 ^ -30. What does very high
resolution mean here? They are trying to read low frequency high
resolution signal, what does that mean? I know what PWM signal is and what
low frequency is, but please explain high resolution? Maybe provide an
exmaple?

Thanks.


If you want to measure the PWM on/off ratio to 1 part in 2^30, that's
about 1 part in 1E9. Not particularly difficult or expensive, but the
measurement might take a bit of time. You need a fairly stable
timebase (but nowhere near 1 part in 1E9) and to accumulate the on and
off times. If you used a timebase in the 50-100MHz range you could get
a measurement in less than a minute.

As suggested, it depends on how quickly you want the answer.

If this is a stable (slowly changing) PWM, then you can sample over
many cycles and total the HI and LOWs (assumes uncorrelated sampling)

If you want to see state of the art, look at Agilent (ex HP) Frequency Counters. These deliver 10-12 Digits per second, and resolve to 150ps

You could even do this Analog, these days, the TI ADS1282
specs 31 bits of Analog Precision, (no missing codes).

Also, keep in mind how the PWM Originated, as there will be
a jitter/noise figure for the signal you are measuring.

-jg

.

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