Abstract
This Letter presents a 12b-control ultra-low-power low-noise two-stage single-ended to differential switched-capacitor variable gain amplifier (SC-VGA) for 2–6-MHz second harmonic cardiac imaging ultrasound probes in 0.18 μm complementary metal oxide semiconductor. The proposed SC-VGA consists of inverters and capacitor (CAP) arrays. By adopting inverters instead of operational trans-conductance amplifiers (OTAs) in traditional SC-amplifiers, both the power and noise are significantly improved. Each stage has a 6b binary-weighted CAP array, and in total the 12b CAP arrays achieve the dB-in-linear gain range from − 21 to 21 dB. The CAP array is divided between the upper 3b and lower 3b by a CAP to decrease the capacitance spread. The total power consumption is 150 μA at 1 V supply voltage, and the input referred noise is 6.5 nV/√HZ at 4 MHz. The second harmonic distortion (HD2) has the mean value − 77 dB at the 460 mV peak-to-peak output swing for 50 samples of Monte Carlo mismatch simulation with a 30 MHz sampling frequency.
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