A one-step input matching method for cascode CMOS low-noise amplifiers

Ming Chang Sun*, Ying Haw Shu, Shing Tenqchen, Wu Shiung Feng

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review


In the design of cascode CMOS low-noise amplifiers, the gate-drain capacitance is generally neglected because it is thought to be small enough compared to gate-source capacitance. However, a careful examination will reveal the fact that the drain impedance of the input transistor significantly affects the input impedance through the gate-drain capacitance, especially as the CMOS technology getting more and more advanced. Moreover, the substrate coupling network of the input transistor also comes into play when the drain impedance of the input transistor is high enough compared to the substrate coupling network. In order to make input matching easier, it is desirable to know the details of the substrate coupling network. Unfortunately, designers generally do not have enough information about the technology they have used, not to mention knowing the details concerning the substrate coupling network. As a matter of fact, designers generally do have foundry provided component models that contain information about the substrate coupling network. This gives us the chance to minimize its effect and predict the input impedance of a low noise amplifier more accurately. In this paper, we show that the effect of the substrate coupling network can be ignored by keeping the drain impedance of the input transistor low enough and a proper drain impedance can then be chosen to achieve input matching without the need of iteration steps. Simulation results of a 2.4 GHz CMOS low noise amplifier using foundry provided component models are also presented to demonstrate the validation of the proposed input matching method.

Original languageEnglish
Pages (from-to)420-427
Number of pages8
JournalIEICE Transactions on Electronics
Issue number3
StatePublished - 2005


  • CMOS
  • Cascode
  • Input matching
  • Low noise amplifier
  • Radio frequency


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