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. Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
If someone says they are trying to read PWM input with very hig resolution(2 ^ 30), I think they meant 2 ^ -30. What does very hig resolution mean here? They are trying to read low frequency hig resolution signal, what does that mean? I know what PWM signal is and wha low frequency is, but please explain high resolution? Maybe provide a exmaple?
Thanks.
High resolution PWM sampling could mean, that someone can measure the duty cycle with high resolution. E.g. with a resolution of 2^30 it would be possible to measure differences of 100%/2^30 in the duty cycle, which I think is impossible or at least very very expensive.
-- Frank Buss, fb@frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de
Could it be they simply mean the number of bits used for the data acquisition ?
-- :wq ^X^Cy^K^X^C^C^C^C
2^30 is meaningless/pointless. PWM resolution of 2^16 is quite practical. Resolution is the ability to measure the difference between 2^30 and (2^30) -1
Is there a reason why you can't ask them yourself?
The nature of your question suggests that either you or they are at least a little bit confused.
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
"> You could even do this Analog, these days, the TI ADS1282
If the OP doesn't even understand the concept of pwm resolution, how is he going to make use of a 31 bit A/D ?
Quick, tell me who is selling a 31 bit A/D, and for how much? :-)
--
[mail]: Chuck F (cbfalconer at maineline dot net)
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Try the download section.
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