DC-to-5-GHz Variable Gain Amplifier for High Speed DSO

Abstract

This paper presents the design of a variable gain amplifier for the frontend circuitry of 5-GHz high-speed digital storage oscilloscopes. The design challenge includes wide bandwidth and low distortion over the frequency range from dc to 5 GHz. The Cherry-Hooper amplifier configuration is used to tackle the issue. The designed variable gain covers the specified range from -2 to 38 dB. The gain flatness carries out ripples less than 1 dB. To verify our approach, two versions of the amplifier circuits are fabricated. With four cascaded stages, the maximum gain achieves larger than 40 dB. The circuits are designed in 0.35 mu m SiGe technology.