Inverter-based low-noise, 150 µW single-ended to differential SC-VGAs for second harmonic cardiac ultrasound imaging probes

摘要

This paper presents two inverter-based low-noise, low-power, single-ended to differential switched-capacitor variable gain amplifiers (SC-VGAs) for 2–6-MHz second harmonic cardiac ultrasound imaging probes fabricated with 0.18 µm complementary metal–oxide–semiconductor technology. By employing inverters in class C mode instead of operational trans-conductance amplifiers, the power consumption of 150 µW at a supply voltage of 1 V is achieved for both VGAs; −75 and −72 dBm of integrated noise with 2–6-MHz bandwidth at maximum gain and a sampling frequency of 30 MHz are achieved for VGA1 and VGA2, respectively. Both VGAs have two stages. VGA1 uses a fully switched-capacitor approach for gain control, and the gain range is −21–21 dB with 12-bit capacitor arrays. VGA2 adopts an inverter-based SC-VGA in the first stage with a 6-bit capacitor array to tune the gain from −9 to 9 dB, and the second stage is a differential amplifier with a 4-bit thermometer-coded resistor array to tune the gain from 0 to 13 dB. Both SC-VGAs complete the single-ended to differential conversion in the second stage to suppress the second harmonic distortion (HD2). Both VGAs have HD2 less than −50 dB. The die size of VGA1 is 245 µm × 134 µm, and the die size of VGA2 is 109 µm × 164 µm.