A novel CMOS exponential transconductor which employs only three NMOS transistors operating in weak inversion, is presented. The main advantage of the proposed circuit is its wide range of exponential behavior, which reaches up to five decades of current range, and above 10 µA to an input voltage range of 800 mV. The physical realization is achieved in two forms: in the first one, the circuit is implemented with discrete MOS transistor arrays by CD4007 series; in the second one, the circuit is fully integrated in a 0.5 µm CMOS standard process. Simulated and experimental results of the proposed exponential transconductor are also presented.