Low Voltage Bandgap Reference Circuit Using Extraction
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Solution Overview
Problem
Existing bandgap voltage reference circuits face limitations in operating at low supply voltages due to high flicker noise and process sensitivity, especially when using MOS devices in current mirror configurations.
Innovation Solution
A circuit and method that generates a temperature-independent bandgap voltage reference using a voltage-to-current converter, differential voltage dividers, and a PTAT loop with bipolar junction transistors, eliminating active MOS devices from the feedback loop to reduce flicker noise and process sensitivity, allowing operation at low supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If MOS devices are used as current mirror in current mode bandgap reference, then the circuit can operate at low supply voltage (1V), but the flicker noise increases substantially and process sensitivity worsens
Solution Approach 1:
The patent removes MOS devices from the feedback loop entirely, extracting the source of flicker noise. The feedback loop uses only passive components (resistors and capacitors) to perform temperature compensation, while MOS devices are confined to the voltage-to-current converter stage where they do not generate harmful noise in the reference output path.
Solution Approach 2:
The patent introduces an intermediate voltage-to-current converter stage that acts as a mediator between the input voltage and the feedback loop. This converter uses MOS devices only in the non-critical input stage, while the feedback loop itself uses passive components as intermediaries to perform temperature compensation without generating flicker noise.
2Temperature
If MOS devices are used as current mirror in current mode bandgap reference, then the circuit can operate at low supply voltage (1V), but the process sensitivity increases
Solution Approach 1:
The patent extracts MOS devices from the feedback loop where they would degrade matching properties. The feedback loop uses only passive resistors and capacitors that have better matching characteristics, thereby reducing process sensitivity while maintaining low supply voltage operation capability.
Solution Approach 2:
The patent applies different device types in different locations: MOS devices are used only in the voltage-to-current converter where threshold voltage variations are less critical, while passive components are used in the feedback loop where matching precision is paramount for temperature compensation.
3Object-generated harmful factors
If voltage mode bandgap reference is used, then the flicker noise is reduced, but the minimum supply voltage increases to at least 1.4V
Solution Approach 1:
The patent merges the advantages of both voltage mode and current mode approaches. It uses a voltage-to-current converter (current mode feature) followed by a feedback loop with passive components (voltage mode feature), combining the low supply voltage capability with the low flicker noise characteristic.
Solution Approach 2:
The patent introduces a voltage-to-current converter as an intermediary stage that enables low supply voltage operation without requiring MOS devices in the feedback loop. This intermediary allows the circuit to operate at 1V while maintaining the low flicker noise benefits of passive component-based feedback.
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 solution achieves lower flicker noise, reduced process sensitivity, and extended operating temperature range, enabling bandgap voltage reference circuits to function effectively at supply voltages as low as 1.2V with improved noise performance and stability across various temperature and voltage conditions.
Implementation Method 1
a first differential voltage divider configured to scale down a first base-emitter voltage of a first bipolar junction transistor biased by the first reference current to generate a first scaled base-emitter voltage; a second differential voltage divider configured to scale down a second base-emitter voltage of a second bipolar junction transistor biased by the second reference current to generate a second scaled base-emitter voltage
Data Source
AI summary
A circuit and method for a bandgap voltage reference operating at 1 volt or below is disclosed, wherein the operational amplifier (A1) drives resistors (R2, R3) only so that both the flicker noise contribution and the process sensitivity due to the conventional metal oxide semiconductor (MOS) devices used as a current mirror within the proportional-to-absolute-temperature (PTAT) loop are eliminated. Two symmetric resistive divider pairs formed by (R1A/R1B, R2A/R2B) are inserted to scale down both the base-emitter voltages (VEB1, VEB2) of bipolar transistors (Q1, Q2) and the PTAT current (IPTAT) so that an output reference voltage (VREF) becomes scalable. Proper bias currents through transistors (M3, M4), which are used to bias (Q1, Q2) and (R1A/R1B, R2A/R2B) respectively, are produced by an additional V-I converter (319) using VREF itself, resulting in a final process, voltage and temperature (PVT) insensitive output reference voltage.