Introductory Concepts in ADS Simulation-Based Submicron Design of MOSFET Amplifiers

Most, if not all, MOSFET models, valid for submicron analysis and design, are too complex to allow analytic solutions. Short-channel devices, with the 0.5 μm BSIM3 model, perform drastically differently than their counterpart long-channel devices that obey the Level 1 model. In particular, as the channel becomes smaller, both the small-signal transconductance gain and the output resistance get smaller, which makes it hard to design single-stage amplifiers that deliver sizable gains. This chapter looks at three load architectures of CS amplifiers – resistor load, diode-connected load, and current source load. The chapter demonstrates how ADS can be used as an active simulation-based design platform. The key ideas of simulation-based design are to (i) thoroughly characterize (via multiple sweep studies) some of the key parameters of the loading MOSFET, including small-signal operating point parameters; (ii) use an ADS tool Swept Optimization capabilities to run multiple optimization studies for multiple sets of design parameters; (iii) create slider-based user interfaces; and (iv) take into account MOSFET drain and source contact resistances.