Voltage Reference Circuit Power Supply Rejection
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Solution Overview
Problem
Prior voltage reference circuits do not provide sufficient power supply rejection, leading to variations in the reference voltage due to input voltage variations.
Innovation Solution
A voltage reference circuit utilizing a differential pair of NPN bipolar transistors with a delta Vbe generation circuit, an operational amplifier, and a current source, along with resistors and diodes, to minimize variations in the reference voltage by regulating the collector voltage of the transistors and using a current mirror configuration to improve power supply rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bandgap reference is used in the voltage reference circuit, then the circuit can provide a stable reference voltage, but the power supply rejection is insufficient and variations in reference voltage occur due to input voltage variations
Solution Approach 1:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the voltage at the base of the NPN bipolar transistor and adjusts the gate voltage of the PMOS transistor to maintain a constant voltage difference. This closed-loop feedback system compensates for input voltage variations, thereby improving power supply rejection and stabilizing the reference voltage output.
Solution Approach 2:
The patent utilizes the temperature-dependent behavior of the base-emitter voltage (Vbe) of the NPN bipolar transistor in conjunction with the gate-source voltage (Vgs) of the PMOS transistor. By carefully selecting transistor dimensions and biasing conditions, the circuit exploits parameter changes in these voltages with temperature and input voltage to achieve compensation and improve power supply rejection.
2Reliability
If the circuit uses a differential pair configuration with operational amplifier and current mirror, then power supply rejection is improved by approximately 7 dB, but the device complexity increases
Solution Approach 1:
The patent divides the voltage reference circuit into distinct functional modules: a differential pair stage for voltage comparison, an operational amplifier for error amplification, a current mirror for biasing and signal replication, and a PMOS transistor for output regulation. This segmentation allows each module to perform its specific function efficiently while making the overall complex circuit more manageable and analyzable.
Solution Approach 2:
The patent combines multiple functions into integrated structures where possible. For example, the operational amplifier and current mirror share common biasing networks and transistor pairs, and the PMOS transistor serves both as the regulated output device and as part of the feedback loop. This merging reduces the total component count and interconnection complexity while maintaining the improved power supply rejection performance.
Data Source
AI summary
In one embodiment, a voltage reference circuit is configured to use two differentially coupled transistors to form a delta Vbe for the voltage reference circuit.