Square wave peak voltage value

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

  1. Dollarday

    Thread Starter Member

    Jan 25, 2012
    Hi people! :D

    Can you please help me with the following problem:

    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 :cool:

  2. wayneh


    Sep 9, 2010
    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


    Mar 14, 2008
    You could use an analog sample-and-hold or a peak-hold circuit.
  4. ramancini8


    Jul 18, 2012
    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.
    Dollarday likes this.