120dB Pseudo-Logarithmic Amplifier
designed by:
Zachary Richards
A project for
ECE 547: VLSI Design and Layout
Spring 2007
University of Maine
Department of Electrical and Computer Engineering
The pseudo-logarithmic amplifier designed for this project is comprised of a cascade of
thirteen current limiting amplifiers and a simple op-amp. The output currents of the limiting
amplifiers are summed together creating the pseudo-logarithmic behavior, which is described in
detail in the project report.
There are two such summation currents and these are used to develop two voltages which serve as
inputs to a difference amplifier, which is realized with the simple op-amp.
This pseudo-logarithmic amplifier accepts a single input current over a 120dB range, 1nA to 1mA,
and produces a single output voltage between 0 and 4V which is linear-in-dB with the input.
Because the cascade utilizes thirteen stages for this dynamic range, the error in the resultant
pseudo-logarithmic approximation is nearly negligible (see "Results" in project report).