Switched-Capacitor Bandgap Reference Circuit Chopping Offset
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Solution Overview
Problem
Conventional bandgap reference circuits suffer from significant temperature drift due to offset errors in CMOS operational amplifiers, which affect the stability of output voltages.
Innovation Solution
A method and apparatus that utilize a switched capacitor circuit with chopped operational amplifiers and capacitive elements to average voltages with PTAT and CTAT components, canceling out residual offset components to generate a reference voltage independent of operational amplifier offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bandgap reference circuit uses a CMOS operational amplifier to generate PTAT voltage, then the circuit can provide stable operating voltages, but the offset of the CMOS op-amp results in significant temperature drift
Solution Approach 1:
The patent applies periodic action through chopping techniques that modulate the operational amplifier offset at a specific frequency. By periodically switching the offset component to an AC signal, the DC offset error is converted to an AC signal that can be filtered out, thereby reducing temperature drift while maintaining voltage stability
Solution Approach 2:
The patent introduces an intermediary filtering mechanism that selectively removes the offset frequency component from the output signal. This mediator (filter) allows the useful PTAT and CTAT voltage components to pass through while blocking the offset-induced temperature drift component
2Temperature
If the offset of the CMOS op-amp is reduced, then temperature drift decreases, but circuit complexity increases
Solution Approach 1:
The patent changes the frequency parameter of the offset signal through chopping, transforming it from a DC component to an AC component at a specific frequency. This parameter change enables selective filtering without requiring complex circuit modifications, thus reducing temperature drift with minimal increase in circuit complexity
Solution Approach 2:
The patent replaces complex physical offset cancellation mechanisms with a simpler frequency-based filtering approach. Instead of using complex matching networks or multiple compensation circuits, the solution substitutes a frequency-domain separation method that is easier to implement and less complex
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 effectively reduces temperature drift and stabilizes output voltages by canceling out residual offset components, resulting in a reference voltage that is substantially independent of operational amplifier offsets, thus improving the accuracy and reliability of bandgap reference circuits.
Implementation Method 1
coupling a first end of a first capacitive element to the first output node according to a first switching signal, and coupling a first end of a second capacitive element to the first output node according to a second switching signal
Data Source
AI summary
A method includes providing a first voltage to a first output node during a first time interval, providing a second voltage to the first output node during a second time interval, and averaging the first and second voltages to provide a reference voltage to a second output node. The first voltage includes a proportional-to-absolute-temperature (PTAT) component, a complementary-to-absolute-temperature (CTAT) component, and a first residual offset component. The second voltage includes the PTAT component, the CTAT component, and a second residual offset component. An apparatus includes a discrete-time circuit to provide the first voltage to the first output node during the first time interval and to provide the second voltage to the first output node during the second time interval, and a filter to average the first and second voltages to provide the reference voltage to the second output node.