PhotoDiode Amplifier with Data Compression Explained

An Example implementation of Avalanche PhotoDiode Amplifier with Data Compression is discussed in this video. This Log compression transimpedance amplifier is designed with three Op Amps, two matched NPN Bipolar Junction Transistors, a Zener Diode and a Temperature Compensating Tempco resistor with positive temperature coefficient. The Tempco resistor compensates the BJT thermal voltage linear dependency on temperature. If temperature compensation is not required, then instead of TempCo resistor, a nominal 1kohm resistor with small tolerance (for example less than or equal 1%) can be used. A combination of OpAmp virtual short and negative feedback, Shockley PN junction equation and Kirchhoff Circuit Laws (KCL and KVL) are used to analyze this Log amplifier circuit and to prove that it is operating as a Transimpedance amplifier with an out put voltage Vo=Log10(1mA/Ipd) where Ipd is photodiode current that varies from 100 nano ampere to 1 mA in this design. For more examples see @STEMprof Analog playlist https://www.youtube.com/playlist?list=PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt . Notice that both Zener Diode and Avalanche Photo Diode are properly reversed biased in this analog circuit.