Class-E amplifier design for efficient CMUT transmission and wide band operation

• Published in: Analog integrated circuits and signal processing 2022, Vol.110 (1), p.139-149
• Main Authors: Khan, Mansoor, Agha, Shahrukh
• Format: Article
• Language: English
• Subjects: Circuits and Systems; Electrical Engineering; Engineering; Signal,Image and Speech Processing
• ISSN: 0925-1030; 1573-1979
• DOI: 10.1007/s10470-021-01952-6

This paper investigates the design of a Class-E amplifier to be used to drive a CMUT element. An important parameter of amplifier design is the load which determines the overall noise performance, bandwidth of CMUT operation and its transmit efficiency. Airborne CMUTs unlike PZTs have a large capacitive reactance at resonance along with the radiation resistance. We employ a simple LC section between the amplifier output and CMUT input to cancel the capacitive reactance and transform its radiation resistance to any desired amplifier load. Class-E amplifier can then be designed for the given transformed load. In this work we show that higher transformed CMUT loads have lower radiated power with increased 3-dB bandwidth and improved overall noise performance of amplifier and CMUT system. We use lumped equivalent circuit model of CMUT in air to determine the input impedance of CMUT at resonance and then transform its impedance to various design load values. Harmonic balance circuit simulations results show that CMUT 3-dB bandwidth increases from 14 kHz to 44 kHz with fractional loss of amplifier reducing from 6.8 % to 0.14 % when designed with a 500 Ω transformed load instead of 10 Ω . However the radiated power decreases from 4.92 μ W to 0.14 μ W at the same frequency.