Precision references for mixed -signal integrated circuits
This dissertation presents an array of research to meet the challenges of references in mixed-signal integrated circuits. First, a design methodology combining intuition and mathematical analysis is proposed for creative analog integrated circuit design. A system-level and device-level mixed-mode simulation technique as well as some supporting tools are presented to accelerate the exploring of new design ideas. Then the challenges for references in mixed-signal integrated circuits are addressed in two areas. One area is the voltage reference and the other area is the reference amplifier which generates reference currents from a reference voltage. Voltage references in both CMOS and GaAs processes are covered to provide on-chip references. A new architecture for voltage references in CMOS processes which is different from the traditional bandgap reference is proposed. This architecture does not use parasitic bipolar transistors and can be implemented in standard CMOS processes. Design issues for the implementation of bandgap references in GaAs HBT processes are then reviewed. First the temperature characteristics of a GaAs bandgap voltage reference are presented with measured data. Then two architectures for high gain (over 80 dB) operational amplifiers are proposed to meet the challenge of lack of P-type devices in GaAs HBT processes. The first architecture uses resistive load and has multiple gain stages. A new compensation scheme for multi-stage operational amplifiers is proposed and a closed loop stability criterion is used. The second architecture uses a synthesized high impedance load. The synthesized load uses only NPN devices and has the advantage of small area and low power consumption. While conventional reference amplifiers only emphasize the static performances, the research in this dissertation emphasizes the importance of dynamic performance of reference amplifiers. It is shown the bandwidth of a reference amplifier is an essential factor for the dynamic performance of mixed-signal integrated circuits. An open loop architecture for the reference amplifier is proposed for good static and dynamic performance. The designed reference amplifier has a high bandwidth of 2.5 GHz and is demonstrated to be able to reduce the settling time of mixed-signal integrated circuits.