Universal exponential function implementation using highly-linear CMOS V-I converters for dB-linear (AGC) applications

A universal exponential function generator is introduced which is implemented by low-voltage (less than or equal to 3V) low-power CMOS widely-linear-input voltage-to-current converters. The Taylor's series expansion is used for the exponential function approach. The proposed exponential circuit is composed of a V-I squarer circuit, a linear V-I converter and a constant current biasing to synthesize the second-order, the first-order and the zero-order terms in Taylor's series. In a 1.2 mu m n-well CMOS process, at the entire voltage control range, the dB-linear function achieves 20dB range, the linearity error is less than +/-0.5% within 12dB. The total power consumption is below 0.9mW with 3V supply voltage.