Exponential function generator embodied by using a CMOS process and variable gain amplifier employing the same

摘要

An exponential function generator embodied by a CMOS process and a variable gain amplifier (VGA) employing the same. Since it is difficult for CMOS devices to attain an exponential function by themselves, the exponential function generator employs a scheme of generating two voltage signals varying with different slopes for a control voltage and summing up the two voltage signals so as to obtain an approximated exponential function. Further, the VGA is designed capable of being implemented by the CMOS process and performs only fixed gain amplification at an input stage by considering the deterioration of features of CMOS devices, linearly changes the gain by providing an exponential control current to a variable gain cell performing the practical gain variation for its bias control, and constructs a load by using FETs operating in an ohmic region to perform a stabilized operation regardless of variations in external factors.