Description.

For EE 105 class, our final lab projects consisted of Single-stage, Cascode, and Multi-stage MOS amplifiers designs.

Design Process.

In preliminary labs, we characterized vital device behaviors and parameters for a diode and a BS170 NMOS using a Semiconductor Parameter Analyzer (Agilent 4155C) with SpaZilla, a LabVIEW program, for instrument control and data acquisition, and simulated the device in Cadence to compensate the non-idealities for a reliable design.

Once enough information is gained of our devices, we started to construct our amplifier circuits. From the DC perspective, we first ran a few theoretical calculations to determine the values (or ranges of values) of our circuit components that grantees the operation of the NMOS in its saturation region using the DC Operating Point information and the simplified MOSFET DC model; from the AC perspective, given the design specifications (Low-pass Cutoff Frequency, High-pass Cutoff Frequency, Midband Gain, Output Swing), we further specified the values (or ranges of values) of our circuit components based on the small-signal model of MOSFETs.

Picking a few sets of parameters that optimizes the design based on our calculations, we constructed our circuit in Cadence and ran a few simulations to verify that our design choices meet the specifications and fine-tune for non-idealities.

Finally, we built our circuit on breadboard and used standard testing equipments (multimeter, function generator, DC power supply, Oscilloscope) to verify our build. In this process, we discovered that the actual behavior of the BS170 NMOS we were offered in the lab is way-off from the theoretical values and Cadence simulated values due to poor quality controls and manufacturing variations. We had to experiment with different MOSFETs and make trial-and-error adjustments to our original designs based on the actual readings of the testing equipments.

By iterating the process above, we were able to design and build a single-stage, a cascode, and a multi-stage MOSFET amplifier with 28% better performance than the specifications on average.