Investigation of Constant Transconductance Circuit for Low Power Low-Noise Amplifier

In this paper, the design of wide-swing constant transconductance (gm) bias circuit that generates bias voltage for lownoise amplifier (LNA) circuit design by using an off-chip resistor is demonstrated. The overall transconductance (Gm) generated by the constant gm bias circuit is important to maintain the overall gain and noise figure of the LNA circuit. Therefore, investigation is performed to study the variation in Gm with process, temperature and supply voltage (PVT). Temperature and supply voltage are swept from -10 °C to 85°C and 1.425 V to 1.575 V respectively, while the process conditions are also varied to the extreme and the gm variation is eventually concluded at between -3% to 7%. With the slight variation in the gm value, through simulation, at worst condition of state SS, we are able to attain a conversion gain (S21) variation of -3.10% and a noise figure (NF) variation of 18.71 %. The whole constant gm circuit draws approximately 100μA from a 1.5V supply and is designed based on 0.13μm CMOS process. Keywords—Transconductance, LNA, temperature, process.