Design of a front-end analog channel with 80MHz bandwidth in digital oscilloscope

Abstract

Aiming at the requirement of a high-frequency input analog signal conditioning in digital oscilloscope, an analog channel design with high bandwidth and large dynamic range is proposed. The analog channel is used to realize high-frequency analog signal converting to the best sampling range of high-speed ADC which is mainly composed of direct or passive attenuation circuit, impedance conversion circuit, digital step attenuator and fixed gain amplifier circuit. Emphasis on using OrCAD PSpice tool to build analog channel circuits and carry out functional simulation verification, high-frequency PCB circuit board is fabricated according to the simulation results, and output analog signals are measured when analog signals of different frequencies pass through the analog channel PCB circuit board. At the same time, adjusting the adjustable capacitor can make output analog signal flatness performance of frequency response curve better in the entire bandwidth, and I successfully give a good frequency response curve of the analog channel circuit by actual measurement results.