Abstract
This paper presents a novel amplifier that satisfies both low distortion and high efficiency for high-frequency wireless ultrasound systems with limited battery life and size. While increasing the amplifier efficiency helps to address the problems for wireless ultrasound systems, it can cause signal distortion owing to harmonic components. Therefore, a new type of class F amplifier is designed to achieve high efficiency and low distortion. In the amplifier, the resonant circuit at each stage controls the harmonic components to reduce distortion and improve efficiency. Transformers with a large shunt resistor are also helpful to reduce the remaining noise in the input signal. The proposed class F amplifier is tested using simulations, and the voltage and current waveforms are analyzed to achieve correct operation with adequate efficiency and distortion. The measured performance of the class F amplifier has a gain of 23.2 dB and a power added efficiency (PAE) of 88.9% at 25 MHz. The measured DC current is 121 mA with a variance of less than 1% when the PA is operating. We measured the received echo signal through the pulse-echo response using a 25-MHz transducer owing to the compatibility of the designed class F amplifier with high- frequency transducers. The measured total harmonic distortion (THD) of the echo signal was obtained as 4.5% with a slightly low ring-down. The results show that the low THD and high PAE of the new high-efficiency and high-voltage amplifier may increase battery life and reduce the cooling fan size, thus providing a suitable environment for high-frequency wireless ultrasound systems.
Highlights
Ultrasounds are widely used because of their many useful features such as low cost and realtime characteristics in everyday life
The center frequency was 25 MHz and the harmonic components were varied using a resonant circuit composed of CF and LF (Class F amplifier network in Fig 5), and it was tuned to minimize the overlap of the drain source voltage and rectification waveform
For frequency ranges from 15 MHz to 35 MHz, the total harmonic distortion (THD) and power added efficiency (PAE) are measured in increments of 1 MHz
Summary
Ultrasounds are widely used because of their many useful features such as low cost and realtime characteristics in everyday life. The center frequency was 25 MHz and the harmonic components were varied using a resonant circuit composed of CF and LF (Class F amplifier network in Fig 5), and it was tuned to minimize the overlap of the drain source voltage and rectification waveform. A high-efficiency and high-voltage class F amplifier was designed to operate at 25 MHz. the variation of the output amplitude with frequency was analyzed to determine its suitability for use at 25 MHz. In addition, the class F amplifier and transducer were used together to analyze the THD and pulse echo signal waveforms [17]. Non-linear devices generate more noise in highfrequency environments, and the efficiency of the ultrasound system during high-frequency operations decreases significantly at low bias supply voltages [21] If nonlinear devices such as expanders and limiters are used, various factors need to be considered. The 3 cylces pulses generated from the class F power amplifier was the input for a 25 MHz transducer
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