Operational amplifier is a powerful tool to perform different mathematical operations on analog signals. In this post we will discuss about circuit to implement voltage ratio or voltage division using operational amplifiers.
Let us design a circuit to implement the following expression
We will use the property of "logarithm" to implement division. And voltage difference circuit to offset Vref.
We know that log(A) - log(B) = log(A/B).
In our problem,
Let us design a circuit to implement the following expression
Vout = (V1-Vref)/ (V2-Vref)
We will use the property of "logarithm" to implement division. And voltage difference circuit to offset Vref.
We know that log(A) - log(B) = log(A/B).
In our problem,
A = V1 - Vref
B = V2 - Vref
First stage is a difference amplifier which subtract Vref from V1 and V2 respectively. This gives us voltage Va and Vb.
The second stage performs logarithm of input voltage to obtain Va' and Vb'.
The final output voltage will be Va'-Vb'.
By setting suitable value of gain factor (-kT/q) and resistance ratio in previous stages, we can get the required expression of voltage division at the out.
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