Design and Performance Optimization of Low Phase Noise SiGe HBT Amplifiers for Si-Photonics Integrated Opto-Electronic Oscillator
Authors:   , Bulsara Devan , Daryoush Afshin S. 
Published: November 2022

Highly stable radio-frequency (RF) local oscillators (LO) are critical for low error rate digital signal detection systems. For example, a highly stable clock signal is required for sample and hold of analog signals while superheterodyne detection systems require coherent LO's for terrestrial, deep space, and Wi-Fi communication. Opto-electronic oscillators (OEO) are well known for their broadband frequency tuning and low aperture jitter characteristics. To design a stable LO (StLO), any phase errors that contribute to the phase modulation (PM) of the oscillation frequency must be minimized. Any low frequency noise could be upconverted to the RF carrier frequency using nonlinear phase modulation to phase error (PM-PM) and amplitude modulation to phase modulation (AM-PM) conversion. To reduce the overall noise added into the StLO, RF circuit design should consider devices manufacturing process with low amplitude and phase noise at given optimum operation point of transistor and appropriate amplifier design topologies. The goal of this thesis is to explore optimum amplifier designs with low phase noise that could be integrated as part of a self-forced OEO design. This amplifier is designed using silicon germanium (SiGe) heterojunction bipolar transistor (HBT) technology from low-phase noise perspective. The RF integrated circuit (RFIC) is based on the TowerJazz (now Tower) foundry service. Key elements for the optimal performance of the HBT include optimization of gain and low noise based on transition frequency (fT), maximum frequency (fmax), maximum stable gain, minimum noise figure, and its phase variation sensitivity with the operation point variation of HBT transistor to DC bias point variations. An optimal bias point is found by considering reduced phase error due to the transistor operation point. Using the optimal HBT bias point of operation, a variety of Class A amplifiers are considered for high linearity. Particularly amplifiers including common emitter, cascade, and transimpedance amplifier (TZA) are analyzed in terms of operation from 1mA to 30mA and compared in terms of gain, noise figure, and AM-PM conversion contribution to single sideband (SSB) phase noise at various bias. All predicted SSB phase noise reported in this thesis are at 100kHz offset of 10GHz carrier frequency. Actively biased single stage CE amplifier has a simulated gain of 14.3 dB and a noise figure of 1.6 dB at 12mA. In terms of the nonlinear mixing of low frequency noise as a PM-PM conversion, the actively biased single stage amplifier has a phase noise contribution of -147.8 and -167.25 dBc/Hz with respect to the upper and lower sidebands, respectively. This amplifier design also has an AM-PM conversion contribution to phase noise of -328 dBc/Hz. In addition, the design of a cascade amplifier provided a gain as high as 28.4 dB and a noise figure of 2.9 dB at 10 GHz with the calculated SSB phase noise associated with the AM-PM conversion of -82 dBc/Hz. When considering the TZA, a broadband transimpedance of 11 dB [omega] is predicted over 2 to 18 GHz. The TZA design also is seen to have an AM-PM conversion contribution SSB phase noise of -141 dBc/Hz. The TZA cascaded with previously designed single stage amplifier provides a transimpedance of 18.6 dB [omega] at and SSB phase noise due AM-PM conversion of -102 dBc/Hz at 10 GHz. Lastly, a TZA cascaded with the dual-stage amplifier design was designed in this work to provide a transimpedance of 25.4 dB [omega] at 10 GHz. At this frequency, an AM-PM conversion contribution to SSB phase noise of -90 dBc/Hz was observed.