| PhD Viva

Name of the Speaker: Ms. Madhavi Kadam (EE15D037)
Guide: Prof. Sankaran Aniruddhan
Online meeting link: https://meet.google.com/oey-bnqj-eiw
Date/Time: 12th January 2024 (Friday), 2:00 PM
Title: A 26GHz Compact Bidirectional TRX Front end Based on a Reflective Transmission Line Phase Shifter

Abstract

This talk starts with the design and analysis of a 28GHz CMOS Low noise differential amplifier is discussed. A current reuse technique is used to minimize power consumption by stacking two common source amplifiers. The proposed LNA is designed in a 65nm RF CMOS process to achieve an output matched voltage gain of 18.5dB and minimum Noise figure (NF) of 4.6dB. The LNA consumes 10mW from a 1.2V power supply and exhibits an input-referred 1dB compression point of -16.1dBm. The LNA is designed using transmission lines, inductors, high-Q capacitors, and a transformer, and occupies a total area of only 0.33mm^2.

Phased array system improves the signal-to-noise ratio in the receiver (RX) and increases effective isotropic radiated power (EIRP) in the transmitter (TX). A critical building block in TRX arrays with RF-path phase shifting is the RF phase shifter (VPS), which must provide a 360 degree phase shift range in addition to low insertion loss, high linearity, high resolution and low power consumption. In this work, we have implemented a 28GHz reflection type transmission-line (TL) based phase shifter (RTTLPS), and it is presented as the next topic. The proposed architecture employs a completely passive approach to double the phase shift achievable using a TL when compared to conventional architectures. The phase shifter, along with a preceding low noise amplifier and buffer, is implemented in a 65nm CMOS process. The fabricated chip achieves a measured phase resolution of 11.25 degree at 28GHz, with an rms error of 3 degree and a total phase shift of degree. The insertion loss of the phase shifter alone is 17dB. The active area of the entire phase shifter, including LNA and buffer, is 0.41mm^2. Later, transmission-line based reflection-type phase shifter for the 2.5 to 3.2GHz frequency band is discussed. Open and short reflective loads are used to double the available phase shift and reduce insertion loss. The transmission line is implemented using inductors and MOS switches in a 65nm RF CMOS process. This work achieves a total phase shift of 180 degree with phase resolution of 22.5 degree at 2.85GHz and rms error of 1.2 degree. The insertion loss of the phase shifter is 5.7dB and the loss variation is less than 0.3dB. Then finally presents a 24.25-27.5GHz area and power-efficient phased array bidirectional transceiver front end without an explicit T/R switch or matching networks. The bidirectional circuit uses three mutually coupled inductors for the input and output matching network, reducing die area significantly. Varactor tuning is employed in the passive reflective type switched transmission line-based phase shifter for improved resolution. In measurements, the achieved saturated output power and power-added efficiency in TX-mode are 12 dBm and 13.1%, respectively. The RX-mode noise figure is 9.6dB at 26GHz. The fabricated chip achieves a measured phase resolution of 2.8 degree at 26GHz, with an RMS error of 0.6 degree and a total phase shift of 180 degree. The insertion loss of the phase shifter alone is 13dB. The active area of the entire phased array bidirectional front-end transceiver is 0.38mm^2, which makes it ideal for large phased array systems.