Logarithmic Amplifier 2.4 2000/08/08 2004/08/10 08:48:37.472 GMT-5 Don Johnson dhj@rice.edu Carol Bettoney carolrb@alumni.rice.edu Don Johnson dhj@rice.edu Logarithmic amplifiers

Diode Circuit

Here is a circuit involving a diode that is actually simpler to analyze than the previous one. We know that the current through the resistor must equal that through the diode. Thus, the diode's current is proportional to the input voltage. As the voltage across the diode is related to the logarithm of its current, we see that the input-output relation is v out k T q v in R I 0 1 Clearly, the name logarithmic amplifier is justified for this circuit.