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 1.8 V at 0.18 mum CMOS process. The LNA was designed using power-constrained noise optimization method in obtaining the width of the transistor of 290 mum. 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 VDD and ground. The input was 50 Omega 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 with 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 S₂₁ 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. S₁₁ 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.