Logarithmic and exponential function generator for analog signal processing

摘要

The logarithmic and exponential function generator for analog signal processing is implemented with CMOS circuits operating in current mode and includes current mirrors connected to a square root function circuit and two current amplifiers. A third current amplifier utilizes a constant current input. The outputs of the current amplifiers are combined to provide the logarithmic and exponential functions.

主权项

1. A logarithmic and exponential function generator for analog signal processing, comprising:
a pair of current mirrors having an input accepting an input current Ix and providing first and second output currents, both of the output currents being Ix; a square root current amplifier circuit having an input accepting the first Ix output current, a normalizing input accepting a current Iy, and providing a square root output characterized by the expression:α⁢⁢Iy⁢IxIy,where α is a current gain provided by the square root current amplifier circuit;
a linear current amplifier accepting the second Ix output current as input and having an output characterized by the expression:
βIx,where β is a current gain provided by the linear current amplifier;
a DC current amplifier accepting a DC current I0 as input and having an output characterized by the expression:
γI0,where γ is a current gain provided by the DC current amplifier, the outputs from the square root current amplifier circuit, the linear current amplifier, and the DC current amplifier being summed to provide a total output characterized by the expression:α⁢⁢Iy⁢IxIy+β⁢⁢Ix+γ⁢⁢I0,where α, β and γ are selected so that the total output expression represents an approximation of a function selected from the group consisting of a logarithmic function and an exponential function.