Multiplying and Dividing Voltages

albertleng 21 years ago

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

Vote

CJT 21 years ago

Read the chapter on op amps.

The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form che...@prodigy.net.

Vote

Robert Baer 21 years ago

Most especially concerning log and anti-log amps. Hint: antilog( log(a) + log(b) ) --> a * b

Vote

Timo Neuvonen 21 years ago

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)

-- TiN

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required