Design of Robust CMOS Amplifiers Combining Advanced Low-Voltage and Feedback Techniques

Abstract

Abstract. This paper describes and tries to demystify the use of different lowvoltage operation devices, such as dynamic threshold MOS transistors (DTMOS) with feedback techniques such as regulated-feedforward (RFF) and self-biasing (SB). Traditionally, DTMOS devices are only used when nominal supply voltages below 0.7 V are envisaged. Moreover, RFF and SB techniques are normally avoided since engineers designing high-performance amplifiers are afraid of additional stability concerns. This work demonstrates, through exhaustive simulation results over process, temperature and supply (PVT) corners using a standard 130 nm 1.2 V CMOS technology that, employing DTMOS in some specific devices can improve some performance parameters such as the open-loop low-frequency gain and, simultaneously, reduce significantly the variability over PVT corners. Moreover, it is also demonstrated that, there is no risk of operating at supply voltages higher than 1.2 V. Combining DTMOS with RFF and SB allows achieving reasonable gainbandwidth products (GBW) even operating at low-voltage (down to 0.7 V), together averaged power savings of the order of 8% and highly simplifies the design of the circuit (since no biasing circuitry is required).

Stability Improvements in a Rail-to-Rail Input/Output, Constant Gm Operational Amplifier, at 0.4 V Operation, Using the Low-Voltage DTMOS Technique

“…The low-voltage DTMOS technique was chosen as the approach to use because of the simplicity of the implementation, since it basically consists in disconnecting the bulks of the PMOS and NMOS devices, respectively from and V SS , and re-connect them to the gate terminal [4,5].…”