Low-Voltage Bandgap Reference Circuit with Feedback Amplifier
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Solution Overview
Problem
Existing voltage reference circuits, such as the Brokaw reference, are not compatible with integrated circuit devices requiring voltage references lower than 1.2 V, and previous low voltage references have high manufacturing variations necessitating expensive trimming for precision.
Innovation Solution
A low-voltage bandgap reference circuit using three bipolar junction transistors and a feedback amplifier to regulate a reference voltage rail, achieving temperature compensation for output voltages below 1.2 V without the need for trimming, by utilizing a Vbe loop branch and a ΔVbe loop branch with a fractional base-emitter voltage to balance collector voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Brokaw voltage reference is used, then a stable voltage reference around 1.25V is provided, but it is not compatible with devices requiring voltage references lower than 1.2V
Solution Approach 1:
The patent changes the operating parameters of the bandgap reference circuit to achieve output voltages below 1.2V. By modifying the resistor ratios and transistor configurations in the feedback network, the circuit can regulate output voltages in the range of 0.8V to 1.2V while maintaining temperature compensation and precision, thus resolving the contradiction between precision and voltage range adaptability.
2Adaptability or versatility
If previous low voltage references are used, then voltage references below 1.2V are achieved, but manufacturing variations cause much higher spread requiring expensive trimming
Solution Approach 1:
The patent employs a feedback amplifier that senses the output voltage and adjusts the reference voltage rail to maintain precise regulation. This feedback mechanism compensates for manufacturing variations in real-time, eliminating the need for trimming and reducing voltage reference spread caused by manufacturing tolerances.
Solution Approach 2:
The circuit performs preliminary temperature compensation and voltage regulation through the feedback amplifier and properly biased transistors, pre-correcting for expected variations before they affect the output. This preliminary action eliminates the need for post-manufacturing trimming.
3Measurement precision
If trimming is applied to achieve precision in low voltage references, then desired precision is obtained, but die area, equipment, and test time increase
Solution Approach 1:
The feedback amplifier and temperature-compensated circuitry automatically adjust and regulate the output voltage without external intervention. The circuit serves itself by continuously monitoring and correcting its own output, eliminating the need for external trimming operations and reducing device complexity.
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 provides a temperature-compensated low-voltage reference with accuracy better than ±1% and eliminates the need for trimming, allowing for precise regulation of output voltage below 1.2 V in integrated circuits.
Implementation Method 1
a feedback amplifier (S) that regulates the reference voltage rail to equalize collector voltages of the first and second bipolar junction transistors
Implementation Method 2
providing a first base emitter voltage (Vbe1) with a first bipolar junction transistor (Q1)... providing a second base emitter voltage (Vbe0) with a second bipolar junction transistor (Q0)
Data Source
AI summary
A low-voltage bandgap reference circuit includes a current source supplying a reference voltage rail. A first BJT has a collector coupled to the voltage rail via a resistor, a base coupled directly to the voltage rail, and an emitter coupled to ground via an emitter resistance. A second BJT has a collector coupled to the voltage rail via a resistor, a base coupled to voltage rail by a first base resistance and to ground via a second base resistance, and a collector coupled to the emitter resistance via an intermediate resistance. A third BJT has a collector driven by a current source, a base coupled to a node between the first and second base resistances, and an emitter coupled to ground. A feedback amplifier regulates the reference voltage rail to equalize collector voltages of the first and second BJTs.