Bandgap Reference Circuit With Cascode Decoupling for Stable PSR
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Solution Overview
Problem
Conventional bandgap reference circuits face challenges in achieving stable and reliable power supply rejection (PSR) performance, especially in environments with variable supply voltages, due to coupling between the supply voltage and the collector terminal of bipolar transistors, leading to current mismatches and reduced accuracy.
Innovation Solution
A single-stage bandgap reference circuit architecture using NPN bipolar transistors with a decoupling stage, where the transistors are decoupled from the supply voltage node using NMOS cascode transistors controlled by the bandgap voltage, improving PSR performance and reducing current consumption and area impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuits are used with direct coupling between supply voltage and bipolar transistor collectors, then the circuit structure is simple, but power supply rejection (PSR) performance is poor and current mismatch occurs
Solution Approach 1:
The patent introduces decoupling transistors as intermediary elements between the supply voltage node and the bipolar transistor collectors. These decoupling transistors act as mediators that block the direct coupling path, preventing supply voltage variations from affecting the collector nodes. The control terminals of these decoupling transistors are driven by voltages that are insensitive to bandgap voltage variations, ensuring stable current mirrors while maintaining PSR performance.
Solution Approach 2:
The patent segments the circuit into distinct functional blocks: the bandgap core circuit, the decoupling stage with separate decoupling transistors for each collector, and the current mirror circuit. This segmentation allows independent optimization of each block - the bandgap core generates the reference voltage, the decoupling transistors provide PSR, and the current mirrors ensure current matching, thereby resolving the contradiction between simplicity and performance.
2Reliability
If decoupling transistors are added to improve PSR performance, then power supply rejection improves by up to 40 dB, but circuit area and current consumption increase
Solution Approach 1:
The patent applies decoupling transistors locally only at the collector nodes where PSR is most critical, rather than throughout the entire circuit. Each decoupling transistor is strategically placed to protect specific bipolar transistor collectors from supply voltage variations. This localized application achieves the required PSR performance (up to 40 dB improvement) while minimizing the overall circuit area impact compared to a comprehensive decoupling approach.
3Measurement precision
If decoupling transistors are added to reduce current mismatch, then bandgap voltage accuracy improves, but current consumption increases
Solution Approach 1:
The patent carefully selects and optimizes the parameters of the decoupling transistors, including their size ratios and bias conditions, to achieve the desired current matching precision while minimizing current consumption. The control voltages applied to the decoupling transistors are designed to be insensitive to bandgap voltage variations, ensuring that the decoupling transistors operate in an optimal region that balances accuracy and power consumption. This parameter optimization allows the circuit to achieve high bandgap voltage accuracy without excessive current draw.
Data Source
AI summary
A bandgap circuit includes a supply node as well as a first and second bipolar transistors having jointly coupled base terminal at a bandgap node providing a bandgap voltage. First and second current generators are coupled to the supply node and supply mirrored first and second currents, respectively, to first and second circuit nodes. A third circuit node is coupled to the first bipolar transistor via a first resistor and coupled to ground via a second resistor, respectively. The third circuit node is also coupled to the second bipolar transistor so that the second resistor is traversed by a current which is the sum of the currents through the bipolar transistors. A decoupling stage intermediate the current generators and the bipolar transistors includes first and second cascode decoupling transistors having jointly coupled control terminals receiving a bias voltage sensitive to the bandgap voltage.