CMOS Exponential Function Circuits and Their Applications

This dissertation developed some new circuits for generation of exponential function and their applications. Since the exponential function circuits were traditionally implemented by using of the bipolar technology. However, in the past decade, CMOS technology has become the major trend of modern circuit design. Therefore, it would be beneficial to use CMOS technologies rather than bipolar technologies to implement the exponential function circuit.
In the beginning, the possible methods of generating the exponential function in CMOS technology have been discussed, such as the approximated Taylor’s series expansion, pseudo-exponential function and the voltage and current characteristics of the MOSFET in weak inversion are also mentioned. Secondly, based on the Taylor’s series expansion, two different exponential function circuits have been developed. Next, a “1/x” circuit, which can be used to realize the pseudo-exponential function, is proposed. Based on the proposed “1/x” circuit, both the current and voltage-control exponential function circuits can be implemented. The applications of the exponential function circuits are proposed in Chapter 4, which includes two variable-gain amplifiers and a voltage-to-current converter. Finally, the conclusions are given in Chapter 5. All the proposed circuits have been fabricated in the 0.5 mm 2P2M CMOS process. The experimental results are in consistent with the theoretical analysis.