To Design a Cascode LNA by Using Channel-Length-Split Device with Constant-gm in a 0.35 μm Silicon CMOS Technology

In the paper, the folded-cascode low-noise operational amplifier (LNA) with constant-gm is proposed and analyzed. The channel-length split technique adopted to expand ratio of W/L of the differential pair transistor to improve the performance of LNA for the gain bandwidth product, noise and offset voltage. The channel-length split method is separated differential input transistor into 2 transistors in series. The area of the transistor (W, L) can be properly increased to effectively decrease the flick noise. The double indirect-frequency compensation technique and the clamping circuit are adopted in amplifier to increase the bandwidth. The proposed two sets input differential pair can be provided a constant-gm value and rail-to-rail swing during the operating region. The floating-point structure is used to reach rail-to-rail swing at output stage. Simulation results show that the gain, constant-gm in input stag, noise, offset-voltage, PSRR, CMRR and ICMR of amplifier are improved. The characteristics of LNA are successfully verified by the TSMC 0.35um 2P4M CMOS technology. There have a great potential in the VLSI implementation used in the portable electronic and bio-medicine product applications.