Sub-bandgap Voltage Reference Circuit for Low-Voltage Operation
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Solution Overview
Problem
Conventional bandgap reference circuits are not suitable for supply voltages lower than 0.9 V, as they cannot maintain stability and temperature insensitivity at sub-1 volt operation, which is required for modern low-power and low-voltage IC designs.
Innovation Solution
A low-voltage sub-bandgap voltage reference circuit is designed using a differential amplifier and bipolar transistors with a DC bias circuit to maintain base-emitter voltage by applying a negative DC bias between the base and collector terminals, allowing operation at or below 0.9 V without compromising temperature or electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuits are used, then stable reference voltage around 1.2V is achieved, but operation at supply voltage lower than 0.9V is not possible
Solution Approach 1:
The patent applies parameter changes by modifying the operating parameters of the bandgap reference circuit to enable sub-0.9V operation. Specifically, the circuit uses a modified topology with transistors operating in different regions and adjusted biasing conditions to achieve stable reference voltage generation at supply voltages as low as 0.8V, extending the adaptable supply voltage range below the conventional 0.9V limit.
2Use of energy by moving object
If supply voltage is reduced to meet low-power objectives, then power consumption is reduced, but reference voltage stability and temperature insensitivity deteriorate
Solution Approach 1:
The patent employs feedback mechanisms through the differential amplifier configuration and carefully designed transistor biasing networks to maintain reference voltage stability at low supply voltages. The feedback loops compensate for variations and ensure that the reference voltage remains insensitive to temperature and supply voltage changes, even when operating at reduced power consumption levels.
3Adaptability or versatility
If conventional bandgap reference circuits operate at sub-1 volt, then low voltage operation is achieved, but temperature characteristics and electrical characteristics are compromised
Solution Approach 1:
The patent modifies the circuit parameters including transistor sizing ratios, biasing voltages, and resistor values to optimize the temperature compensation mechanism for sub-1V operation. These parameter adjustments ensure that the PTAT and CTAT components properly cancel temperature dependencies even at reduced supply voltages, maintaining temperature insensitivity that conventional circuits cannot achieve.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed circuit effectively operates at supply voltages as low as 0.8 V across a range of temperatures without degrading electrical or temperature-related characteristics, enhancing the low VDD characteristic while maintaining stability and insensitivity to temperature variations.
Implementation Method 1
By canceling the negative temperature dependence of the PN junctions in one group of transistors with the positive temperature dependence from a PTAT (proportional-to-absolute-temperature) circuit which includes the other group of transistors, a fixed DC voltage output, Vref, which doesn't change with temperature is generated.
Data Source
AI summary
A low-voltage sub-bandgap reference circuit is disclosed. In one embodiment, the low-voltage sub-bandgap voltage reference circuit includes a differential amplifier and a first bipolar transistor with its base and collector coupled to an electrical ground. The reference circuit further includes a second bipolar transistor with base and collector coupled to the electrical ground. The reference circuit further includes a DC bias circuit supplying a predetermined voltage output between a high and low voltage terminal, the high voltage terminal being coupled to both collectors of the first and second bipolar transistors and the low voltage terminal being coupled to both bases of the first and second bipolar transistors.