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Multiplying and Dividing Voltages

Discussion in 'Electronic Equipment' started by [email protected], Dec 15, 2004.

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  1. Guest

    Hi mates.

    Albert's here. I'm new here and i'm seeking your helps regarding the
    following.

    I'm working on a project which involves the arithmetic operations (+,
    -, X, /) on voltages. Using ADC conversion is not applicable in my
    case. The project is to capture 4 voltages from 4 testpoints from a
    PCBA, ie A, B, C and D. After capturing the 4 voltages, we need to do
    the following calculations:

    Result = ((A+B)-(C+D))/(A+B+C+D)

    For the addition and subtraction parts, i've got the idea of using
    summing amplifier and inverting amplifier to perform the functions. If
    you have other suggestion, kindly share with me. Fyi, the voltage
    values are about 0.3V.

    For the multiplying & division's parts, please give suggestion for the
    circuit.
    Thanks and hope to get your response soon.

    Cheers,
    Albert Leng
     
  2. CJT

    CJT Guest

    Read the chapter on op amps.
     
  3. Robert Baer

    Robert Baer Guest

    Most especially concerning log and anti-log amps.
    Hint: antilog( log(a) + log(b) ) --> a * b
     
  4. Most especially concerning log and anti-log amps.
    In principle, yes. In practice, it may be difficult -or at least not
    practical, depending on application.

    Things to evaluate:
    - in how many quadrants does the multiplier need to work (posite and
    negative input voltages possible)
    - how wide dynamic range is requided, 10dB (eg. 1V...3V) or maybe 80dB
    (1mV...10V)
    - which accuracy is required
    - which temperature range is required (log amps tend to be error-prone with
    varying temperature)
    - required speed (~bandwith, which is somehow not-so-exact function with log
    amps)

    Possible workarounds to avoid log amps:
    - if low accuracy and dynamics is enough, linearized model tuned to correct
    operating point
    - piecewise-linear approach
    - digital approach (adc + digital math + dac)
     
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