A Two Stage Variable-Gain Low-Noise Amplifier for X-Band in 0.18 µm CMOS

In this paper a variable gain low noise amplifier (VG-LNA) is designed and analyzed for X band in 0.18 µm CMOS technology. A two-stage structure is utilized in the proposed VG-LNA and its gain, which is controlled by an on-chip voltage (Vcnt), has continuous and almost linear variations. The required range for Vcnt can be initiated from 0.5 V, also the variations of gain doesn’t ruin reflection loss (S11), return loss (S12) and noise figure (NF). The best performance of this VG-LNA is at 10 GHz frequency with 1 GHz bandwidth. In the center frequency, the maximum gain is 20.8 dB that continuously and linearly decreases to 4 dB by increasing Vcnt. Also S11 and S12 in this frequency are lower than −27 and −38 dB, respectively. NF is lower than 2 dB in the mentioned frequency range and NFmin is equal to 1.2 dB, while the third-order intercept point (IIP3) equals to 8.27 dBm in the best condition and always stays above −10 dBm. The main advantage of the proposed structure in compare with the similar structures is not only the key parameters don’t ruin by the gain variations, but also increment of Vcnt operation range (0.5 V to Vdd), leads to expanding gain control range. These results are achieved while the power consumption is 8.4 mW with 1.8 V supply voltage and the chip area is 0.56 mm2.