Abstract
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.
Published Version
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