Project 3: Stability, Programmability, and further Amplifier Design

The goal of this project is to understand stability in amplifier design, as well as its implications for realistic analog design (e.g. parastic capacitors). Further, this project explicitly allows using Floating-Gate (FG) circuit techniques in the designs, although not required for the design project. You might find having these techniques helpful for your specifications.

Course Materials

Taped Lectures

Reading Material

Lecture Boards

Design Project

You will have two designs to consider for this project. Both designs require analysis, simulation, and IC layout. You will use the same You will use your previous IC process as well as simulation parameters for this design.

In both cases, you must demonstrate stability. You must show the step response for your designs. Stability is defined as Q <= 1, which is equivalent to at least 45 degrees of phase margin. For the amplifier design, this stability should be demonstrated for the amplifier connected as a unity gain amplifier. For both designs, Area must be calculated and minimized.

Analytic Questions

These analytic questions will be quite helpful for you to understand your Transimpedance Amplifier design. You are Strongly encouraged to work through these questions before starting your design. The Questions will directly connect to Figure 1. For the analytic questions, assume the ratio between C1 and C2 is 10. Assume typical device parameters ("kappa", "sigma") throughout the analysis. You will be looking at large-signal and small-signal analysis approaches through these questions.

Figure 1: Two candidate transimpedance circuits to convert an input current to an output voltage. (a) Basic transimpedance circuit. (b) Frequency dependant transimpedance circuit. High-frequency gain is higher than low-frequency gain.

Floating-Gate Circuit Design

This section is to start getting you use to working with Floating-Gate (FG) circuit techniques. These techniques allow the user to program an analog value into a circuit. Biasing techniques become straightforward if the required FG infrastructure if available. In the next project, we will talk about how to integrate these devices into a programming infrastructure.

Transimpedance Amplifier Specific Items

You will be designing the four transistor transimpedance amplifier. A few key points for this design: For a particular design, you will be given You need to choose your Vt for your required bias current. You need to minimize your bias current, and how you minimize the bias current is part of your grade. You need to measure your noise level, and minimize where possible. You can add transistors, work with the W/L of the transistors, etc. Don't forget your cascode transistor. Aamplifier parameters for all teams:

Folded-Cascode Specific Items

The design is a differential input, single-ended output amplifier. Some specifications are

In addition each group will be assigned for additional specifications; these specifications will be sent by email to the class. These specifications include

Part of the grade will be on the creativity of the design, as well as how well the report is written up.

The noise measurement is input referred, that is, if one has an ideal noise voltage source, it would appear in series with either the input to the positive or negative terminal. Typically from SPICE for a noise measurement, you will get noise / rt(Hz) at the output (we are only assuming thermal noise for this project), so an approximate measurement is to divide by the lowest in-band gain (you have a given -3dB frequency, so take the lowest gain in that region) to get your input referred noise / rt(Hz).

Remember that you will need to provide all biases on chip. Address these issues in terms of area, power, and temperature effect issues. You will need to bias the components in your design, and you are allowed to choose one resistor (as desired for your biasing) for the design. One strong suggestion would be to use a bootstrap current source generator, and use this circuit to bias any cascode elements, if desired.

Your presentation will include the table of all specifications and what specifications you achieved with the resulting data. You need to insert your target numbers for your unique specifications (4 of them; I will check that they are correct). Of course, you need to have supporting evidence for your specifications.

Folded Cascode op-amp parameters for all teacms: