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. 2021 Mar 29;16(3):e0249034.
doi: 10.1371/journal.pone.0249034. eCollection 2021.

High-efficiency high-voltage class F amplifier for high-frequency wireless ultrasound systems

Kyeongjin Kim  1 , Hojong Choi  1
Affiliations

High-efficiency high-voltage class F amplifier for high-frequency wireless ultrasound systems

Kyeongjin Kim et al. PLoS One. .

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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Wireless ultrasonic system block diagram [7,14,15].
Fig 2
Fig 2. The principles by which waveforms are transformed by harmonics.
The VDS is formed by the original signal and the odd harmonic, and the IDS is formed by the original signal and the even harmonic.
Fig 3
Fig 3. Typical network roles for a class F amplifier.
Fig 4
Fig 4. The ideal schematic diagram that is to calculate the drain efficiency of the two-stage class F amplifier which controlled only third harmonic.
Fig 5
Fig 5. Designed two-stage high efficiency and high voltage class F amplifier schematic diagram.
Fig 6
Fig 6. Large-signal LDMOSFET equivalent circuit provided by STMicroelectronics.
Fig 7
Fig 7. Simulation data of high-efficiency and high-voltage class F amplifier.
Red and blue lines represent the drain voltage and drain current, respectively. The voltage and current waveform data from (a) the first stage and (b) the second stage.
Fig 8
Fig 8. Simulation data of high-efficiency and high-voltage class F amplifier.
S parameter used for impedance matching (a) S11, (b) S22.
Fig 9
Fig 9. Block diagram showing amplifier performance measurement.
Fig 10
Fig 10
(a) Measurement environment for manufactured class F amplifier performance and (b) zoomed-in manufactured class F amplifier.
Fig 11
Fig 11. Ultrasonic pulse echo measurement process.
Fig 12
Fig 12. Limiter and expander schematic used in the experiment.
(a) Expander (b) limiter circuits.
Fig 13
Fig 13. Discharged signal and ultrasonic echo signal transmitted and received by a high-efficiency and high-voltage class F amplifier and 25 MHz transducers.
Fig 14
Fig 14. Curves showing variation of POUT and calculated PAE and THD values obtained from high-efficiency and high-voltage class F amplifier with a 7.5 dBm input power according to frequency.
(a) PAE vs. Frequency, (b) THD vs. Frequency, (c) POUT vs. Frequency.
Fig 15
Fig 15. The first echo signal transmitted and received by a high-efficiency and high-voltage class F amplifier and 25-MHz transducers.
Fig 16
Fig 16. FFT spectrum data transmitted and received by a high-efficiency and high-voltage class F amplifier and 25-MHz transducers.
(a) FFT spectrum data for fundamental signal, second harmonic and third harmonic (b) FFT spectrum data enlarged to show bandwidth.
Fig 17
Fig 17
(a) Measured Pout and (b) calculated PAE and gain graphs from high-efficiency and high-voltage class F amplifier with an input frequency of 25 MHz.
See this image and copyright information in PMC

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