A W-Band Vector Modulator Using Short-Channel Transistor Current Sources and Impedance Compensation Varactors

A W-band vector modulator based on vector summing with a Gilbert-cell is presented, in which two kinds of error-reducing schemes are applied to the summing circuit. One is to use current sources made of short channel transistors to take advantage of the channel length modulation effect. The other is to introduce impedance correction varactors at the input. It controls both gain and phase by using a digital-to-analog converter (DAC) which is designed to make the output impedance of the summing circuit constant regardless of states. The intrinsic gain and phase errors are also analyzed with the help of a simple current model of a MOS transistor, which explains the error-reducing schemes. It was implemented in 28-nm CMOS technology, which consumes only 7.7mA of DC and occupies an area of 0.11mm2 (excluding pads). The RMS gain error of 0.1dB and the RMS phase error of 1.3° were measured with 4-bit gain and 6-bit phase controls at 94 GHz, where the gain dynamic range was around 15 dB.