Design Methodology and Circuit Techniques for Any-Load Stable LDO Regulators with Instant Load Control
Igor M. Filanovsky, University of Alberta
Vadim Ivanov Texas Instruments, USA
Application of the structural methodology to the LDO design helps to create a new class of circuits. In application to LDOs, this means the following characteristics: any load stable, instant transient response, large power supply rejection ratio and low noise. The LDOs satisfying these characteristics should be built using two-loop architecture, the loop transfer function should be of the second order, the buffer output impedance should be strongly reduced, the pass transistor should also have a local feedback for reduction of the output impedance, and the circuit should include nonlinear amplifiers to increase the transient performance. The tutorial starts by reviewing the LDOs subcircuits which contribute to improvement of performance parameters: fast transconductance amplifiers, amplifiers stable for any capacitive circuits, nonlinear amplifiers with increasing transconductance. After that a thorough consideration is given to the LDO circuits which include the above mentioned features. This part is finished with the detailed description of a universal LDO based on current redistribution principle. The last chapter consider the adaptive biasing and LDOs using nonlinear cells. The examples presented are the imbedded in SoC LDO for the SRAM unit, (5 ns reaction time on the load steps), radio transmitter (shaping the required noise vs. frequency characteristic) and LDO for memory retention in the shutdown state (300 nA quiescent current). These LDOs can operate with or without off-chip load capacitors; they are robust to the process and temperature variations and portable to any CMOS process. The circuit techniques demonstrated during this course is proven in design of industrial LDOs.
Igor M. Filanovsky is currently a Professor Emeritus at the Department of Electrical and Computer Engineering at the University of Alberta, Edmonton, Canada. He contributed to five books, Sensor Technology and Devices, L. Ristic, Ed.,1994, Analog VLSI: Signal and Information Processing, M. Ismail and T. Fiez, Eds., 1994), The Electronics Handbook, J. Whitaker, Ed., 1996, The Circuits and Filters Handbook, W.-K. Chen, Ed. 2009. He is a co-author of Operational Amplifier Speed and Accuracy Improvement, Kluwer, 2004, and a co-author of Analysis and Design of Quadrature Oscillators, Springer, 2008. He was also a contributor to The Encyclopedia of Electrical and Electronic Engineering, J. Webster, Ed., 1999, and Comprehensive Dictionary of Electrical Engineering, P. A. Laplante, Ed., 1999. In addition, Dr. I.M. Filanovsky is the author or co-author of about 300 publications on circuit theory (theory of approximation, feedback theory, theory and technical applications of oscillations, strongly nonlinear oscillations) and applied microelectronics (analog electronic circuits, oscillators and multivibrators, signal-conditioning circuits for sensors). He has 4 patents on electronic circuits.
Vadim Ivanov received the M.S.E.E. degree and the Ph.D. degree in 1987, both in the USSR. He designed electronic systems and ASICs for naval navigation equipment from 1980 till 1991, and mixed signal ASICS for sensors, GPS/GLONASS receivers and motor control circuits from 1991 till 1995 in St. Petersburg, Russia. He joined Burr Brown (presently Texas Instruments in Tucson) in 1996 as a senior member of technical staff where he designed operational, instrumentation and power amplifiers, and voltage references as well as switching and linear voltage regulators. He has more than 60 US patents on applications of analog circuit techniques. He also authored about 30 technical papers and three books: Power Integrated Amplifiers (Leningrad, Rumb, 1987), Analog System Design Using ASICS (Leningrad, Rumb, 1988), both in Russian, and Operational Amplifier Speed and Accuracy Improvement (Kluwer, 2004).