Design of wideband communication circuits

The wideband wireless communication system (e.g. Ultra-Wideband (UWB)) is becoming popular for its capability to achieve high data rate wireless transmission. With the progress on CMOS technology in recent years, it could achieve comparable performances at high frequencies to other compound materials (e.g. GaAs) but with much lower cost. Therefore, implementing wideband circuits using CMOS technology has become one of the most important topics in the RF circuit design.;In this study, several wideband CMOS circuits along a receiver chain were designed and tested using various novel design techniques. Low noise amplifiers (LNAs) are one of the most critical components in a receiver design. Three LNAs were designed and measured using a 90 nm CMOS technology. The LNAs adopt a modified resistive feedback topology for wideband input matching and gain-bandwidth extension. All of the LNAs were measured with chip-onboard package and electrostatic discharge (ESD) protection diodes at all the ports. Two of the LNAs were designed for the UWB application and one of the LNA was designed for the multiband application. Tradeoffs between the noise figure (NF), bandwidth, and gain will be demonstrated in the proposed LNAs.;Mixers are also of focus in this doctorial research. Several wideband passive mixers were designed and tested. At first, board level mixers using GaN devices were designed and measured. GaN devices have the property of high breakdown voltage. Therefore, they can be used in high power and high linearity applications. The transistors were modeled specially in the linear region to accurately estimate the performance of the passive mixers. Three passive mixers were fabricated using GaN HEMT transistors with different gate lengths. The results show good linearity performance.;Next, two passive mixers were designed and tested using a 0.18 microm CMOS technology. A fundamental passive mixer and a sub-harmonic passive mixer were made. The fundamental passive mixer achieves a very wide bandwidth for UWB devices. The sub-harmonic passive mixer utilizes the second harmonic of the local oscillator (LO) signal achieving a high LO-IF leakage. The chip includes a sub-harmonic mixer, a voltage controlled oscillator (VCO), and a quadrature generation circuitry.;Finally, a wideband VCO and a UWB frequency synthesizer were considered and designed. The switching band VCO implemented in 0.18 microm CMOS achieves a tuning range from 3 GHz to 5 GHz. Switching inductors and capacitors were used to change the oscillating frequencies. Next, a frequency synthesizer used for the multi-band orthogonal frequency division multiplexing (MB-OFDM) UWB system was designed. The simulated synthesizer can generate twelve bands ranging from 3 GHz to 10 GHz using the sub-harmonic mixing technique. Various spurious reduction methods were implemented to reduce the interferences caused by the spurious signals.