A 56-to-110 dB Gain Programmable Gain Amplifier with Second-Order Band Pass Filter for Ultrasonic Sensor Systems

In this paper, we propose a programmable gain amplifier (PGA) for an ultrasonic sensor system that removes DC offset and out-of-band noise through band-pass filtering in automotive applications. The proposed PGA consists of a low-noise amplifier (LNA), a variable gain amplifier (VGA), an RC low-pass filter (LPF), and a voltage buffer. The structure of LNA and VGA is an active band-pass filter (BPF) constructed using an operational transconductance amplifier (OTA) and passive elements. The PGA’s voltage gain and cut-off frequency can be adjusted by controlling the resistor connected to the common-mode voltage, the feedback capacitor, and the OTA compensation capacitor. An AC coupling capacitor is placed at the input stage to eliminate the DC offset and low-frequency noise of the PGA input signal. In addition, by arranging the feedback resistor and the feedback capacitor, the band-pass filtering function is implemented to block out noise at frequencies higher than the signal band. The PGA can adjust the voltage gain with a 6-dB step from 56 dB to 110 dB in the ultrasonic signal band from 30 kHz to 70 kHz. The design is designed in a 0.18-µm CMOS process. The post-layout simulation shows that it consumes a current of 9.7 mA with a 5 V supply voltage.