Department of Electronic Engineering, Gachon University, 1342 Seongnam-daero, Sujeong-gu, Seongnam 13120, Republic of Korea.
Sensors (Basel). 2023 Apr 30;23(9):4438. doi: 10.3390/s23094438.
The gain of class-C power amplifiers is generally lower than that of class-A power amplifiers. Thus, higher-amplitude input voltage signals for class-C power amplifiers are required. However, high-amplitude input signals generate unwanted harmonic signals. Therefore, a novel bias circuit was proposed to suppress the harmonic signals generated by class-C power amplifiers, which improves the output voltage amplitudes. To verify the proposed idea, the input harmonic signals when using a harmonic-reduced bias circuit (-61.31 dB, -89.092 dB, -90.53 dB, and -90.32 dB) were measured and were found to be much lower than those when using the voltage divider bias circuit (-57.19 dB, -73.49 dB, -70.97 dB, and -73.61 dB) at 25 MHz, 50 MHz, 75 MHz, and 100 MHz, respectively. To further validate the proposed idea, the pulse-echo measurements were compared using the bias circuits. The peak-to-peak echo amplitude and bandwidth of the piezoelectric transducer, measured when using a harmonic-reduced bias circuit (27.07 mV and 37.19%), were higher than those achieved with a voltage divider circuit (18.55 mV and 22.71%). Therefore, the proposed scheme may be useful for ultrasound instruments with low sensitivity.
C 类功率放大器的增益一般低于 A 类功率放大器。因此，C 类功率放大器需要更高幅度的输入电压信号。然而，高幅度的输入信号会产生不需要的谐波信号。因此，提出了一种新颖的偏置电路来抑制 C 类功率放大器产生的谐波信号，从而提高输出电压幅度。为了验证所提出的想法，测量了当使用谐波抑制偏置电路（-61.31 dB、-89.092 dB、-90.53 dB 和-90.32 dB）时的输入谐波信号，发现它们在 25 MHz、50 MHz、75 MHz 和 100 MHz 时分别比使用分压器偏置电路（-57.19 dB、-73.49 dB、-70.97 dB 和-73.61 dB）时低得多。为了进一步验证所提出的想法，使用偏置电路比较了脉冲回波测量。当使用谐波抑制偏置电路（27.07 mV 和 37.19%）时，测量到的压电换能器的峰峰值回波幅度和带宽高于使用分压器电路（18.55 mV 和 22.71%）时的幅度和带宽。因此，该方案可能对灵敏度较低的超声仪器有用。
