An Improved Universal CMOS Current-Mode Analog Function Synthesizer Muhammad Taher Abuelma’atti King Fahd University of Petroleum and Minerals, Saudi Arabia and Nawal Mansour Al-Yahia Girls College of Science, Saudi Arabia

Analog nonlinear circuits are widely used in instrumentation, communication, neural networks, signal processing and medical equipment. Diodes and linear resistors, BJTs JFETs, MOSFETs, BiCMOS operational amplifiers, current conveyors and operational transconductance amplifiers are widely used in designing analog nonlinear circuits.

Numerous nonlinear functions can be approximated by:

For example: * For y=1/(1-x), a 0 = a 1 = a 2 = a 3 = a 4 = a 5 =a 6 =1 * For y=ln(1+x), a 0 = 0, a 1 =1, a 2 =-1/2, a 3 = 1/3, a 4 =-1/4, a 5 =1/5, a 6 =-1/6 * For y=cos(x), a 0 = 1, a 1 =0, a 2 =-1/2, a 3 = 0, a 4 =1/24, a 5 =0, a 6 =-1/720

The traditional class-AB current mirror and its modification to provide squaring unit (SU) and current proportional to the input current

Using the translinear principle then:

A normalized current proportional to can be obtained using the square-difference identity. Additional SUs can be used to obtain normalized currents proportional to, and.

Examples with SPICE Simulation Results In the following examples the bias current I q = 1 uA, the input current I in is changing between 0 and 1 uA, the DC supply voltages are 2 V and x= I in / I q.

Subcircuit for realizing y=1/(1-x)

y=1/(1-x) Error < 1% for x<0.5

Subcircuit for realizing y=cox(x)

y=cox(x) Error < 1% for x<1

Subcircuit for realizing y=ln(1+x)

y=ln(1+x) Error < 1% for x<0.675

Conclusion 1.The proposed technique is very flexible. Any nonlinear function can be realized once its Taylor series expansion is obtained. 2.Accuracy can be improved by using additional terms in the Taylor series. 3.No current multipliers are used.