High bandwidth low power operational amplifier design and compensation techniques

The need for high bandwidth operational amplifiers (op amp) exists for numerous applications. This need requires research in the area of op amp bandwidth extension. The exploited method in this thesis uses a class of compensation called Indirect Feedback Frequency Compensation in which the compensation current is fed back indirectly from the output to an internal high impedance node, to extend the bandwidth of an op amp. This work discusses and compares the existing compensation methods for operational amplifiers to the proposed method. Indirect compensation has inherent benefits in regards with power to speed trade-off. The indirect compensated op amps exhibit significant improvements in speed over traditional Miller compensated op amps and result in much smaller layout size and lower power consumption. The technique has been seldom used in the past because a clear methodology for designing such an amplifier has not been provided. This thesis develops the mathematical and analytical insight for designing an operational amplifier with this technique. Further a design procedure is proposed for an operational amplifier using indirect compensation in this thesis. A design strategy and an example illustrate the use of the proposed design procedure. The two stage op amp designed using Indirect Feedback Frequency Compensation achieved a 2 MHz gain-bandwidth product (GBW) driving a large capacitive load (100 pF). The GBW of the op amp was improved by a factor of 10 times compared to the miller compensation scheme. The amplifier documented in this thesis achieved a higher simulated figures-of-merit (FoMs) compared to the state-of –art and can be directly used in integrated systems to achieve higher performance.