4-bit X-band Variable Gain Amplifier with Additional Steering Transistors Based on 90 nm CMOS

This paper presented the results of X-band 4-bit variable gain amplifier (VGA) based on domestic 90 nm CMOS technology. Using of the VGA in the core-chip design can replace digital step attenuator and buffer amplifier. The methods of the amplifier gain control are considered, and the optimal VGA topology is selected. The key to proposed solution is adding the steering transistors at high attenuation states that decrease the gain RMS error. The developed X-band 4-bit VGA performance is comparable with state-of-the-art results: gain is 11 dB, attenuation range is 7.5 dB with 0.5 dB step, input and output return losses are better than -9 dB, output power P1dB is not less 10 dBm, gain and phase RMS errors are 0.25 dB and 2.5°, respectively. The chip size is $1\times 0.9\text{mm}^{2}$ , while power DC consumption is 55 mW. The advantage of the designed circuit is that no additional amplitude control circuit, such as DAC is required.