Patent ID: 8130215

Claim:
A logarithmic amplifier configured to produce a logarithmic output signal that is a logarithmic function of an input signal, the amplifier comprising: a reference signal; a first function generator configured to produce a periodic exponential waveform from the reference signal based upon a resisitor-capacitor time constant, wherein the logarithmic waveform increases from a minimum value to a maximum value in each period; a second function generator configured to produce a pulsed waveform from the exponential waveform, wherein the pulsed waveform has a signal period, and wherein the pulsed waveform comprises a first portion having a first amplitude for a first time period and a second portion having a different amplitude for the remainder of the signal period, and wherein the duration of the first time period is produced by comparing the exponential waveform produced by the first function generator to a scaled representation of the input signal so that changes in the input signal affect the duration of the first time period; and a low pass filter configured to produce the logarithmic output signal as a function of the pulsed waveform, wherein the low pass filter has a cutoff frequency that is less than the frequency of the pulsed waveform to provide the DC component of the pulsed waveform as the logarithmic output signal, wherein the logarithmic output signal is independent of variation in the resistor-capacitor time constant due to changes in temperature.