Tutorial 4: Circuit Techniques for Operational Amplifier Speed and Accuracy Improvement: Analog Circuit Design with Structural Methodology

OpAmp is the main analog building block for both the systems on discrete elements and systems on silicon. The parameters of OpAmp often define and limit the overall system performance. CMOS technology provides an opportunity to use more complex structural solutions and circuit techniques to improve OpAmp accuracy, power/speed ratio, to add new functional advantages, like low voltage supply operation capability or rail to rail input without the switching point, everything for negligible additional component cost. The circuit techniques that will be demonstrated during this course were proven in design of leading industrial OpAmps. These techniques are unified by a common structural design approach, based on the following principles: - system analysis at the high level of abstraction using the graphic tools like signal flow graphs, and generation of the set of equivalent graph modifications, - equivalent graph transformations to the form when every important parameter in the system or the amplifier is controlled by a dedicated feedback loop; - stability of these loops is achieved without compensation capacitors, by using one-stage (preferably current) amplifiers, - system synthesis consists of implementation of the set of the gain structure modifications followed by simulations based on available library of cells, and final selection of the best circuit solutions.