# Square wave peak voltage value

Discussion in 'The Projects Forum' started by Dollarday, Aug 1, 2012.

1. ### Dollarday Thread Starter Member

Jan 25, 2012
32
1
Hi people!

I have an aperiodic square wave communication signal of 3.3V.

The signal has variable (and unknown) DC offset.

I would like to make a circuit that outputs the peak voltage of the signal at ANY given moment.
(For example, if the DC offset voltage is 2,2V, the peak of the square wave is 3,3 + 2,2 = 5,5V and the circuit should output 5,5V)
If the DC offset voltage changes to 1,1 the peak voltage of the square wave is 3,3 + 1,0 = 4,3V and the circuit should output 4,3V)

Any ideas how I might achieve this?

Preferably an analogue solution, the only thing I can come up with is:
a) Use an ADC to sample the voltage over a small timeframe
b) Use a microcontroller and code to find the highest voltage in that timeframe
c) Use a DAC to display the peak voltage

I'm sure someone out there has a more elegant solution

Regards,
Dollarday

2. ### wayneh Expert

Sep 9, 2010
12,377
3,230
So, you want your offset to be determined by ONLY the most recent "low", as opposed to, say, an average of the last 3 lows?

I think your approach is about right. Just keep sampling and accumulate an average (for better precision, to minimize noise) into avgLO unless/until you see a new sample with a value more than, say, 20% higher. Resample into a new container avgHI to accumulate the new average. At any time, you could grab avgHI-avgLO as your best estimate of the ∆.

3. ### crutschow Expert

Mar 14, 2008
13,478
3,365
You could use an analog sample-and-hold or a peak-hold circuit.

4. ### ramancini8 Member

Jul 18, 2012
447
119
Put your signal into an ac amplifier to strip out the dc content, then differentiate the signal (can be one circuit) to obtain a leading edge pulse, Use this pulse to trigger a peak sample hold, use the trailing edge pulse to reset the PSH. All of these circuits can be found in the National Semiconductor Linear Applications book.

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