Low noise, −50 dB second harmonic distortion single-ended to differential switched-capacitive variable gain amplifier for ultrasound imaging

摘要

A low noise, low power, single-ended to differential switched-capacitor variable gain amplifier (SC-VGA) is designed and fabricated in 0.18 μm complementary metal-oxide-semiconductor technology for a 2-6 MHz second harmonic cardiac ultrasound imaging system. The SC-VGA has 10-bit dB-linear gain steps from -14 to 32 dB which are distributed into two stages, and each stage has a single-stage operational trans-conductance amplifier using floating capacitors to save the power and improve the noise performance. The first stage converts the single-ended input to differential outputs with the 2-bit gain control from 0 to 18 dB, and the second stage exploits 8-bit capacitor arrays to control the gain from -14 to 14 dB. The measured results show that the second harmonic distortion is <;-50 dB, the third harmonic distortion is <;-50 dB and the integrated noise from 2 to 6 MHz at the output is -64 dBm at the maximum gain and a sampling frequency of 30 MHz. The simulation results match well with the measured results. The SC-VGA works at a supply voltage of 1.6 V and consumes the current of 900 μA. The die size of the SC-VGA is 387 μm × 502 μm.