Band Gap Reference Circuit Temperature Compensation
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Solution Overview
Problem
The existing band gap reference circuits exhibit insufficient temperature characteristics, with a temperature dependence represented by an upwardly convex curve, leading to fluctuations in output voltage that are not adequately stable across varying temperatures.
Innovation Solution
A current generating circuit comprising a first current source with positive temperature characteristics, a second current source with flat temperature characteristics, and a compensation transistor with a current mirror circuit that generates a compensation current to improve the temperature dependence of the band gap reference circuit, allowing for a current that remains constant at lower temperatures and increases at higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional band gap reference circuit is used, then a reference voltage can be generated that is relatively stable against power supply voltage fluctuation, but the temperature characteristics are insufficient with a non-zero temperature coefficient
Solution Approach 1:
The circuit is divided into multiple functional blocks: a first current source generating current with positive temperature characteristics, a second current source generating current with flat temperature characteristics, and a current mirror circuit. These segmented functional blocks work together to compensate for temperature variations, resolving the contradiction between voltage stability and temperature coefficient.
Solution Approach 2:
The invention changes the temperature characteristics parameter by using a first current source with positive temperature characteristics (increasing with temperature) to compensate for the downward slope of the band gap reference voltage. By adjusting the temperature dependence of current sources, the overall temperature coefficient of the reference voltage is improved.
2Reliability
If the output voltage is stabilized against power supply fluctuation, then power supply rejection is improved, but temperature dependence remains with an upwardly convex curve pattern
Solution Approach 1:
The current mirror circuit provides feedback by mirroring the base current of the compensation transistor and using it to control the first current source. This feedback mechanism adjusts the compensation current based on temperature variations, enabling the circuit to maintain stable output voltage characteristics across different temperatures while preserving power supply rejection.
Solution Approach 2:
The invention combines two different current sources with contrasting temperature characteristics (one with positive temperature coefficient, one with flat temperature coefficient) to create a composite current system. This composite approach allows the temperature-dependent current to compensate for the temperature-induced voltage drift, resolving the stability contradiction.
3Temperature
If a compensation current with positive temperature characteristics is generated, then temperature compensation is achieved, but circuit complexity increases
Solution Approach 1:
The current mirror circuit serves multiple functions: it mirrors the base current of the compensation transistor, provides feedback control to the first current source, and generates the compensation current with positive temperature characteristics. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in circuit complexity while achieving effective temperature compensation.
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 proposed solution significantly improves the temperature stability of the band gap reference circuit, ensuring a more stable output voltage across a wider temperature range, minimizing errors and enhancing the circuit's performance in electronic devices.
Implementation Method 1
a first emitter resistor configured as a polysilicon resistor arranged between the emitter of the second transistor and the second fixed voltage terminal
Data Source
AI summary
A current generating circuit may include a first current source configured to generate a first current having positive temperature characteristics; a second current source configured to generate a second current; a compensation transistor configured as an NPN bipolar transistor, and arranged such that the second current flows through from its collector and its emitter; and a first current mirror circuit configured to multiply a base current of the compensation transistor by a first coefficient so as to generate a third current. The current generating circuit may be configured to output a fourth current that is proportional to the difference between the first current and the third current.