Design, Simulation and Measurement Analysis on the S-parameters of an Inductively-degenerated Common-source Open-drain Cascode Low Noise Amplifier

An inductively-degenerated common-source (CS) open-drain cascode LNA was designed for W-CDMA application. The operating frequency for the design was at 2.14 GHz, which is at the center of the reception range of the W-CDMA standard. The supply voltage is 1.8V at 0.18μm CMOS process. The LNA was designed using power-constrained noise optimization method in obtaining the width of the transistor of 290 μm. Post-layout simulations with distributed resistors and capacitors were performed. On-chip inductors with quality factor of 8 were utilized to resonate with the metal-insulator-metal capacitor (mimcap). The mimcap was also used to isolate V
DD
and ground. The input was 50 Ω matched using the transistor as well as an inductor at the gate and three parallel 1.65 nH inductors acting as a 0.55 nH degeneration inductor at the source. Detailed design steps are described in this paper wih plots of the post-layout simulation and measurement results provided. These plots are analyzed extensively in this paper and justification for the errors are given. The 12.8 dB of S
21
obtained from the post-layout and a much less 7.8 dB from the measurement shows that there is an offset by 5 dB. Derivations are given to show that the unmatched output is the cause of the gain offset. S
11
is measured at -24 dB which is very close to the simulated value of -25.4 dB. The current measured and simulated at a bias voltage of 0.65 V is 4.1 mA.