Abstract
To obtain a high-quality signal from an ultrasound system through the transmitter, it is necessary to achieve an appropriate operating point of the power amplifier in the ultrasonic transmitter by applying high static bias voltage. However, the power amplifier needs to be operated at low bias voltage, because a power amplifier operating at high bias voltage may consume a large amount of power and increase the temperature of the active devices, worsening the signal characteristics of the ultrasound systems. Therefore, we propose a new method of increasing the bias voltage for a specific period to solve this problem by reducing the output signal distortion of the power amplifier and decreasing the load on the active device. To compare the performance of the proposed method, we measured and compared the signals of the amplifier with the proposed technique and the amplifier only. Notably, improvement was achieved with 11.1% of the power added efficiency and 3.23% of the total harmonic distortion (THD). Additionally, the echo signal generated by the ultrasonic transducer was improved by 2.73 dB of amplitude and 0.028% of THD under the conditions of an input signal of 10 mW. Therefore, the proposed method could be useful for improving ultrasonic transmitter performance using the developed technique.
Highlights
An ultrasound system can be represented as a block diagram, as shown in Figure 1 [1,2,3]
Signal distortion occurs when the bias voltage of the gate of the active device in the power amplifier is lower than the threshold voltage; the drain–source channel of the active device is disconnected for a certain period, generating signal distortions from the power amplifiers [13,14,15]
A large amount of DC power is consumed, even when there is no input signal generated from the power amplifier with static bias voltage
Summary
An ultrasound (ultrasonic) system can be represented as a block diagram, as shown in Figure 1 [1,2,3]. The distortion of the output signal can be minimized by increasing the operating point of the active device with higher bias voltage [13,17,18]. There is very high signal distortion with a narrow bandA linearized Class C amplifier was developed for a 25 MHz ultrasonic transducer [28]. Because signal distortion does not cause a fatal problem for low frequency power piezoelectric loads, high efficiency of the class D amplifier was achieved. In a Class B amplifier, the operating point of the active device is adjusted so that the current flows only during the half cycle of the input signal [34]; high efficiency can be achieved; half of the signal is distorted.
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