Design and Performance Improvement of Cascaded Single-Stage Distributed Amplifiers Using Chebyshev Polynomial Approximation

This paper presents an analytical and design-oriented enhancement of the cascaded single-stage distributed amplifier (CSSDA) aimed at improving its gain-bandwidth performance. The proposed approach, referred to as the Enhanced Cascaded Single-Stage Distributed Amplifier (ECSSDA), is based on leaving the input artificial transmission line of the CSSDA open-circuited. This configuration leads to a theoretical 6 dB gain increase at low frequencies due to voltage doubling at the gate of the first stage but also introduces input mismatch and frequency-dependent gain behavior. To overcome these limitations, the transducer gain of the ECSSDA is analytically derived and approximated using Chebyshev polynomials. This approximation can be interpreted as an impedance-shaping technique that stabilizes the frequency response and limits gain ripple up to the cutoff frequency. Circuit-level simulations demonstrate a broadband gain improvement of approximately 7.24 dB and a bandwidth extension of about 3 GHz compared to the conventional CSSDA, while maintaining acceptable matching conditions. Since the proposed method relies on normalized parameters, it can be extended to other transistor technologies and distributed amplifier implementations.