A sub 1V bandgap reference circuit

This thesis proposes a novel technique for a low supply voltage temperature-independent reference voltage. With the scaling of supply voltages, the threshold voltages don’t scale proportionally and thus low supply reference circuits have replaced the conventional bandgap reference circuit. The first chapter of this work discusses the conventional bandgap references (The Widlar and Brokaw references). The terminology used in the bandgap world is introduced here. The second chapter investigates the existing low supply voltage reference circuits with their advantages and the limitations. A table discussing all the investigated circuits is provided towards the end of the chapter as a summary. Chapter Three proposes a novel technique to generate a temperature-independent voltage which does not use an operational amplifier. This chapter also provides a mathematical understanding for behavior of the circuit. Chapter Four talks about two variations of the proposed architecture. These variations are designed in order to improve the performance of the proposed circuit against power supply variations. Each one of them has its own merits and drawbacks. Finally Chapter Five discusses the effects of process variations and transient response of the proposed circuit. A digital trimming scheme using an EE-PROM is proposed to manage almost all of the process variation effects on the circuit

An accurate, trimless, high PSRR, low-voltage, CMOS bandgap reference IC

Bandgap reference circuits are used in a host of analog, digital, and mixed-signal systems to establish an accurate voltage standard for the entire IC. The accuracy of the bandgap reference voltage under steady-state (dc) and transient (ac) conditions is critical to obtain high system performance. In this work, the impact of process, power-supply, load, and temperature variations and package stresses on the dc and ac accuracy of bandgap reference circuits has been analyzed. Based on this analysis, the a bandgap reference that 1. has high dc accuracy despite process and temperature variations and package stresses, without resorting to expensive trimming or noisy switching schemes, 2. has high dc and ac accuracy despite power-supply variations, without using large off-chip capacitors that increase bill-of-material costs, 3. has high dc and ac accuracy despite load variations, without resorting to error-inducing buffers, 4. is capable of producing a sub-bandgap reference voltage with a low power-supply, to enable it to operate in modern, battery-operated portable applications, 5. utilizes a standard CMOS process, to lower manufacturing costs, and 6. is integrated, to consume less board space has been proposed. The functionality of critical components of the system has been verified through prototypes after which the performance of the complete system has been evaluated by integrating all the individual components on an IC. The proposed CMOS bandgap reference can withstand 5mA of load variations while generating a reference voltage of 890mV that is accurate with respect to temperature to the first order. It exhibits a trimless, dc 3-sigma accuracy performance of 0.84% over a temperature range of -40°C to 125°C and has a worst case ac power-supply ripple rejection (PSRR) performance of 30dB up to 50MHz using 60pF of on-chip capacitance. All the proposed techniques lead to the development of a CMOS bandgap reference that meets the low-cost, high-accuracy demands of state-of-the-art System-on-Chip environments.Ph.D.Committee Chair: Rincon-Mora, Gabriel; Committee Member: Ayazi, Farrokh; Committee Member: Bhatti, Pamela; Committee Member: Leach, W. Marshall; Committee Member: Morley, Thoma

A simple bandgap reference based on VGO extraction with single-temperature trimming

Bandgap references are widely used in analog and mixed-signal systems to provide temperature-independent voltage or current reference. In traditional bandgap structure, the base-emitter voltage VBE of a diode is used to generate a complementary to absolute temperature (CTAT) voltage, which reduces as temperature increases. The base-emitter voltage difference ∆VBE between two diodes with the same current but different emitter areas supplies a proportional to absolute temperature (PTAT) voltage. With the proper adjustment of the coefficients of VBE and ∆VBE in a voltage summer, the temperature dependency of the summed voltage can be mostly canceled out and the output voltage can achieve a relative temperature-constant property. However, even though the linear terms of temperature-dependent components in PTAT and CTAT expressions can be canceled out, there are still some high order terms left, which still affect temperature dependency. For this reason, a first-order bandgap reference with only PTAT and CTAT linear term compensation cannot achieve a sufficiently low temperature coefficient (TC), normally ranging from 10ppm/°C to over 100ppm/°C. To achieve higher precision and lower TC, the high order terms also need to be considered and compensated by some techniques. This thesis study describes the development of a high order bandgap structure, including the initial thinking, design flow, equation derivation, circuit implementation, and simulation result

A 1.2-V 10- µW NPN-Based Temperature Sensor in 65-nm CMOS With an Inaccuracy of 0.2 °C (3σ) From 70 °C to 125 °C

An NPN-based temperature sensor with digital output transistors has been realized in a 65-nm CMOS process. It achieves a batch-calibrated inaccuracy of ±0.5 ◦C (3¾) and a trimmed inaccuracy of ±0.2 ◦C (3¾) over the temperature range from −70 ◦C to 125 ◦C. This performance is obtained by the use of NPN transistors as sensing elements, the use of dynamic techniques, i.e. correlated double sampling and dynamic element matching, and a single room-temperature trim. The sensor draws 8.3 μA from a 1.2-V supply and occupies an area of 0.1 mm2

A Radiation hard bandgap reference circuit in a standard 0.13um CMOS Technology

With ongoing CMOS evolution, the gate-oxide thickness steadily decreases, resulting in an increased radiation tolerance of MOS transistors. Combined with special layout techniques, this yields circuits with a high inherent robustness against X-rays and other ionizing radiation. In bandgap voltage references, the dominant radiation-susceptibility is then no longer associated with the MOS transistors, but is dominated by the diodes. This paper gives an analysis of radiation effects in both MOSdevices and diodes and presents a solution to realize a radiation-hard voltage reference circuit in a standard CMOS technology. A demonstrator circuit was implemented in a standard 0.13 m CMOS technology. Measurements show correct operation with supply voltages in the range from 1.4 V down to 0.85 V, a reference voltage of 405 mV 7.5 mV ( = 6mVchip-to-chip statistical spread), and a reference voltage shift of only 1.5 mV (around 0.8%) under irradiation up to 44 Mrad (Si)

Bandgap Reference Design at the 14-Nanometer FinFET Node

As supply voltages continue to decrease, it becomes harder to ensure that the voltage drop across a diode-connected BJT is sufficient to conduct current without sacrificing die area. One such solution to this potential problem is the diode-connected MOSFET operating in weak inversion. In addition to conducting appreciable current at voltages significantly lower than the power supply, the diode-connected MOSFET reduces the total area for the bandgap implementation. Reference voltage variations across Monte Carlo perturbations are more pronounced as the variation of process parameters are exponentially affected in subthreshold conduction. In order for this proposed solution to be feasible, a design methodology was introduced to mitigate the effects of process variation. A 14 nm bandgap reference was created and simulated across Monte Carlo perturbations for 100 runs at nominal supply voltage and 10% variation of the power supply in either direction. The best case reference voltage was found and used to verify the proposed resistive network solution. The average temperature coefficient was measured to be 66.46 ppm/◦C and the voltage adjustment range was found to be 204.1 mV. The two FinFET subthreshold diodes consume approximately 2.8% of the area of the BJT diode equivalent. Utilizing an appropriate process control technique, subthreshold bandgap references have the potential to overtake traditional BJT-based bandgap architectures in low-power, limited-area applications

A simple sub-1V voltage reference

A traditional bandgap reference voltage has a value approximately equal to 1.2V. This is an inconvenient value to obtain in short-channel CMOS circuits where the nominal power supply voltage is 1.2V or lower. Here, a simple circuit is presented to generate a reference voltage between 600mV and 800mV, based on the threshold voltage of a MOS device, which will be suitable for biasing transistors in strong inversion as well as for use in 6-bit data converters needed for high speed data communication systems. The circuit uses a novel, but simple, method for generating the temperature coefficients needed for generating a stable voltage reference across temperature. The core circuit produces a PTAT current that when passed through a diode-connected device, with a CTAT threshold voltage, will produce a voltage that is stable across temperature. The measured results demonstrate an average voltage variation of 4.62mV across five chips, each containing eight voltage reference circuits, and a minimum voltage variation of 1.1mV from 0°C to 80°C. A variation of the proposed circuit replaces the BJTs with MOSFETs to achieve smaller area, and simulation results indicate even less voltage variation across temperature.Electrical and Computer Engineerin

Analysis and Laboratory Verification of Bandgap Prototypes, Circuit Engineering, Optimization of Trimming Process

Lo scopo di questa tesi è la progettazione di due riferimenti di tensione bandgap ad alta precisione e basso consumo in una tecnologia economica. Nella fase di progettazione ogni singolo stadio viene analizzato, ottimizzato e confrontato con altre possibili soluzioni. Vengono inoltre esaminati gli effetti del processo e del mismatch. Per migliorare la precisione vengono studiate due reti di trimming resistivo, la cui verifica è ottenuta mediante un nuovo algoritm