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

Abstract

This paper presents two inverter-based lownoise, low-power, single-ended to differential switchedcapacitor variable gain amplifiers (SC-VGAs) for 2-6-MHz second harmonic cardiac ultrasound imaging probes fabricated with 0.18 lm complementary metal-oxidesemiconductor technology. By employing inverters in class C mode instead of operational trans-conductance amplifiers, the power consumption of 150 lW 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 lm 9 134 lm, and the die size of VGA2 is 109 lm 9 164 lm.

CMOS Inverter as Analog Circuit: An Overview

“…Then, the input-referred noise is obtained by dividing (1) with the trans-impedance gain R as: Nowadays, in order to take advantage of the CMOS inverter in modern process technology, there has been a lot of approaches to adopt CMOS inverter into analog circuits. This paper focuses on the applications of high-speed analog circuits, and introduces three examples of that, amplifier in optical communication receivers [6,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], high-speed clock and data buffer [13,[31][32][33][34][35][36][37][38][39][40][41], and output driver for high-speed I/O transmitter [13,40,[42][43][44][45][46][47][48][49][50].…”

“…Optical receivers presented in [18,19,21,[24][25][26][27] extend the usage of the CMOS inverter to the post limiting amplifier which follows the TIA. In addition, [16,17,30] present resistive-feedback-inverter-based low-noise amplifier (LNA) and variable gain amplifier (VGA), respectively. In such applications, a normal inverter stage and a resistive-feedback stage are placed alternately to retain the self-bias (resistive feedback) as well as high gain (inverter), as shown in Figure 7.…”

Low-Voltage 0.81mW, 1–32 CMOS VGA With 5% Bandwidth Variations and −38dB DC Rejection

“…T HE amplifier is an essential block in analog circuits. In many applications variable gain amplifiers (VGAs) are required with DC rejection, low bandwidth variations over the gain adjustment range, reduced supply voltage and power dissipation, i. e. wireless systems [1] and biomedical systems [2].…”