A ±1V-DC to 20-GHz Front-End Chipset with 1.5-Vpp AC and 0.5-to-1V DC Outputs for Direct Sampling Real-Time Oscilloscopes

This paper presents a 20 GHz DC-coupled RF front-end chipset for direct sampling digital real-time oscilloscopes. The chipset consists of four chips: a DC cancelling amplifier (DCCA), a distributed active balun (DAB), an equalizer, and a dual differential output variable gain amplifier (DDO-VGA). The DCCA cancels the input DC voltage with a range of ±1V. The DAB achieves single-ended to differential conversion in a wideband starting from DC. The DDO-VGA has two well balanced differential outputs with output DC adjustment. All four chips are DC-coupled and the DC voltages in inter-stages are shifted to 0 V. This chipset is prototyped with a 0.10-μm GaAs pHEMT technology. The measurements of the front-end show 4.5-to-6.5dB noise figure, 23-dB gain tuning range, and <1-dB/V gain variation across ±1V input DC over DC-to-20 GHz bandwidth.