Bandgap Voltage Circuit Using Low-Beta Bipolar Device
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Solution Overview
Problem
The existing bandgap voltage reference circuits in integrated circuits suffer from a large tolerance spread due to performance variations in CMOS transistors, leading to increased production costs and complexity, especially when used for over-temperature protection, as trimming techniques are costly and difficult to implement effectively.
Innovation Solution
The spread of the bandgap voltage is reduced by conditioning the biasing current for the target bipolar transistor using a series of transistors with similar characteristics, which compensates for the saturation current using the forward current ratio, thereby reducing the base-emitter voltage spread and eliminating the need for costly trimming processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If trimming techniques (laser fusing, OTP, PROM) are employed to lower the spread of bandgap voltage, then manufacturing precision is improved, but production cost increases and device complexity increases
Solution Approach 1:
The circuit automatically compensates for process variations through the action of the low-beta transistor on the biasing current, eliminating the need for external trimming mechanisms. The system self-regulates by using the transistor's current conditioning effect to reduce bandgap voltage spread without requiring additional trimming circuitry or production steps.
2Manufacturing precision
If trimming techniques are employed to lower the spread of bandgap voltage, then manufacturing precision is improved, but production cost increases
Solution Approach 1:
The low-beta transistor provides automatic compensation for process variations, eliminating the need for costly trimming processes such as laser fusing or OTP. The circuit self-regulates during normal operation, achieving reduced bandgap voltage spread without requiring additional production steps or specialized manufacturing equipment.
Solution Approach 2:
The invention uses a simple low-beta transistor, which is a standard, inexpensive CMOS component, to achieve compensation. This replaces expensive trimming operations with a low-cost transistor that can be easily integrated into the standard CMOS fabrication process without requiring additional production steps.
3Device complexity
If standard CMOS transistors are used to generate bandgap voltage, then device complexity is reduced, but manufacturing precision worsens due to larger tolerance spread
Solution Approach 1:
The invention changes the beta parameter of the transistor by selecting a low-beta transistor from standard CMOS libraries. This parameter change enables the transistor to provide current compensation that reduces bandgap voltage spread, achieving improved manufacturing precision while still using standard CMOS technology without requiring special device types.
4Reliability
If bandgap voltage is used for over-temperature protection, then reliability is improved, but ease of operation worsens due to difficulty in trimming at high temperatures
Solution Approach 1:
The low-beta transistor is configured to provide compensation action before temperature excursions occur. The circuit proactively compensates for process variations under normal operating conditions, ensuring accurate bandgap voltage reference is available when needed for over-temperature protection, without requiring post-fabrication trimming or high-temperature testing.
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
This approach results in a more predictable and precise reference voltage with reduced production costs and improved over-temperature protection, as the bandgap voltage spread is minimized, enhancing the reliability and safety of applications.
Implementation Method 1
conditioning the biasing current for the target bipolar transistor using a series of transistors with similar characteristics, which compensates for the saturation current using the forward current ratio
Implementation Method 2
The temperature positive correlated ΔVBE is a factor of thermal voltage. The ΔVBE can be a constant and independent of process tolerances.
Data Source
AI summary
Representative implementations of devices and techniques provide a reduction in the spread of a bandgap voltage of a bandgap reference circuit. The biasing current for a target bipolar device is conditioned by passing it through one or more like bipolar devices prior to biasing the target bipolar device.