A Circuit with Logarithmic Transfer Response over 9 Decades

The short-circuit collector current of many silicon transistors is proportional to the exponential of the emitter-base voltage over 9 decades of collector current (
10^{-11} a
to
10^{-2} a
). Such a transistor may be connected as a three-terminal feedback network in an operational amplifier to obtain accurate logarithmic transfer response over a dynamic range of 9 decades.