EXPONENTIAL FUNCTION CIRCUITRY

PURPOSE: To obtain a passage current proportional to exponential function of an input current. CONSTITUTION: A square root of multiplier output circuit has an input diode chain 14 and an output diode chain 18, and these diodes are npn type transistors of base emitter junction. Diode chain 14 has two input sub-chains 20 and 22, and has N pieces of diodes. The voltage of the input diode chain 14 at the top part is equal to the voltage of the output diode chain 18 at the top part. Further, the voltage of diode chain 18 at the bottom is made equal to the voltage of diode chain 14 at the bottom by a voltage driving circuit forming a differential amplifier 24. Thus, the voltage drop across both ends of the output diode chain 18 is proportional to the voltage drop across both ends of the input diode chain 14.