A Ka-Band Low Phase-Shift CMOS Variable Gain Low Noise Amplifier

In this paper, a Low Noise Variable Gain Amplifier in Ka-frequency band is designed. This amplifier is digitally controlled by using switching transistors which change the gain with an accuracy of 5-bit resolution (32 steps). The output phase shift should be minimized within a Dynamic Range of 15 dB. The proposed structure includes a Low Noise Amplifier and a Variable Gain Amplifier, with common-source structure and degenerative inductor. In the proposed structure, the main gain is achieved by LNA and the switching control bits are used in two stages of the VGA. Simulation illustrates a Noise Figure of 5. 6 dB; bandwidth of 5. 34 GHz; S11, S22 less than -14 dB and Dynamic Range of 15 dB. By using a “compensating inductor” in the source of switching transistors, the amount of phase shift was reduced, such that within the bandwidth of 1. 5 GHz it is less than 5 degrees. The post-layout simulation results, show a Dynamic Range of 18. 7 dB; a bandwidth of 2. 5 GHz; Noise Figure of 6. 4 dB and return losses less than -10 dB. In addition to it, In EM analysis, all inductors and major RF paths are evaluated by “Sonnet” software.