Low-Voltage Band-Gap Reference Circuit Topology
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Solution Overview
Problem
Conventional band-gap reference voltage bias circuits are ineffective at supply voltages below 1.5 V, making them unsuitable for small-area, low-power chip designs in mobile communication handsets, as they require higher operating voltages and are sensitive to temperature and power supply variations.
Innovation Solution
A low-voltage band-gap reference voltage bias circuit using PMOS transistors, feedback amplifiers, resistors, and bipolar transistors or diodes to generate a stable reference voltage independent of temperature and power supply voltage, with a simple configuration and small layout area, allowing operation at voltages as low as 1 V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional band-gap reference voltage bias circuit is used, then temperature compensation is achieved, but the circuit requires a supply voltage of at least 1.5 V or higher
Solution Approach 1:
The patent changes the operating voltage parameter from conventional 1.5V or higher to sub-1V levels by modifying the circuit topology. It uses a folded cascode structure with PMOS transistors and current mirrors to generate the reference voltage at lower supply voltages while maintaining temperature compensation through the band-gap principle.
Solution Approach 2:
The circuit is divided into functional segments: a current mirror circuit using PMOS transistors, a folded cascode stage, and a reference voltage output stage. This segmentation allows each part to operate efficiently at low voltages while collectively achieving temperature-independent reference voltage generation.
2Reliability
If a conventional band-gap bias circuit is used, then stable reference voltage is provided, but the chip area increases
Solution Approach 1:
The patent merges the current mirror function and the reference voltage generation function into a single integrated folded cascode structure. The PMOS transistors serve dual purposes as both current mirrors and active loads, reducing the overall chip area while maintaining reference voltage stability.
Solution Approach 2:
The circuit components perform multiple functions: PMOS transistors act as current mirrors, active loads, and voltage generation elements simultaneously. This multi-functionality reduces the number of discrete components needed, thereby reducing chip area while maintaining stability.
3Temperature
If a conventional band-gap bias circuit is used, then temperature compensation is achieved, but the circuit complexity increases
Solution Approach 1:
Instead of using the conventional approach of generating reference voltage directly from bipolar transistors, the patent inverts the approach by using PMOS current mirrors to generate and mirror currents that flow through bipolar transistors to produce the reference voltage. This inverted topology simplifies the overall circuit configuration at low voltages.
Solution Approach 2:
The patent introduces PMOS transistors as intermediary elements between the power supply and the bipolar transistors. These PMOS devices act as current mirrors that mediate the current flow, enabling temperature compensation while simplifying the voltage requirements and circuit configuration.
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 circuit provides a stable reference voltage with minimal temperature variation (less than 1%) and independence from power supply voltage fluctuations, enabling efficient operation at sub-1V supply voltages, thus facilitating the design of small-area, low-power chips.
Implementation Method 1
Voltages (i.e. ΔVBE) applied to both ends of the first resistor R1 are amplified by the feedback amplifier AMP
Implementation Method 2
The current supplied to the first resistor R1 is ΔVBE/R1. The current ΔVBE/R1 copies the characteristic of the base-emitter voltage difference ΔVBE and is mirrored to the third PMOS transistor M3
Implementation Method 3
A base-emitter voltage of a bipolar transistor is inversely proportional to temperature
Implementation Method 4
a current supplied to the first resistor R1 is ΔVBE/R1
Data Source
AI summary
A low-voltage band-gap reference voltage bias circuit is provided. In the low-voltage band-gap reference voltage bias circuit, a proportional-to-absolute temperature (PTAT) current is copied to two nodes, respectively, to generate a first voltage having a negative slope with respect to temperature variation, and a second voltage having a positive slope with respect to temperature variation, and first and second elements having high impedances are serially connected to each other between the two nodes, such that the sum of the negative slope of the first voltage and the positive slope of the second voltage is zero and an average voltage between the two nodes is extracted to output the extracted result as a reference voltage. Accordingly, a stable reference voltage of 1V or lower regardless of a power supply voltage and temperature variation can be supplied.