Self-Starting Bandgap Reference Circuit Eliminates Start-Up Delay
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Solution Overview
Problem
Conventional bandgap references require start-up circuits to operate, which are difficult to design and evaluate, and introduce delays and undesired zero-current or zero-voltage states, making them unreliable, especially in situations with unreliable power supply or radiation exposure.
Innovation Solution
A self-starting bandgap reference circuit that uses a bias current source to drive core bipolar junction transistors with independent current sources, eliminating the need for a start-up circuit by ensuring a stable current drive and avoiding zero-current states, and includes methods to extract and scale the ΔVBE signal for temperature independence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap references use current mirrors to create PTAT current, then the circuit can generate temperature-compensated reference voltage, but the circuit introduces zero-current stable states requiring start-up circuits
Solution Approach 1:
The patent extracts and eliminates the problematic zero-current stable state from the bandgap reference circuit by replacing the conventional current mirror configuration. The core insight is to remove the feedback mechanism that creates the unwanted equilibrium point at zero current, thereby eliminating the need for external start-up circuits while preserving the temperature compensation function.
Solution Approach 2:
Instead of using a current mirror to copy and feedback current (conventional approach), the patent inverts the approach by using independent current sources that directly establish the desired current relationship without feedback. This inversion of the control mechanism eliminates the stability issue at zero current while maintaining the PTAT current generation.
2Reliability
If start-up circuits are added to conventional bandgap references, then the zero-current state problem is solved, but the circuit design becomes more difficult and introduces delays
Solution Approach 1:
The patent makes the bandgap reference circuit self-starting by designing the core circuitry to inherently avoid zero-current stable states. The circuit serves itself by establishing non-zero current operation through its own internal structure without requiring external start-up assistance, thereby eliminating both the design complexity and time delays associated with traditional start-up circuits.
3Measurement precision
If conventional bandgap references use feedback circuits to stabilize current, then current accuracy is improved, but the circuit becomes more sensitive to radiation and power supply variations
Solution Approach 1:
The patent replaces the feedback control mechanism (analogous to a mechanical control system) with a direct current source approach. By substituting the feedback loop with independent current sources that directly establish current relationships, the circuit achieves current accuracy without the sensitivity to external disturbances that characterizes feedback-based systems.
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 stable voltage reference independent of supply voltage and temperature, eliminating the need for start-up circuits and ensuring radiation tolerance, with no undesired zero-current or zero-voltage states, suitable for both bipolar and CMOS technologies.
Implementation Method 1
Bandgap references are based on temperature behavior of the base-emitter voltage (VBE) of a bipolar junction transistor. When biased in a stable manner, VBE falls with increasing temperature. Thus, VBE is said to have a temperature behavior that is Complimentary to Absolute Temperature (CTAT).
Implementation Method 2
A bipolar junction transistor collector current is given by the following equation: IC=Is*exp(VBE/Vt) wherein, IC is the collector current, Is is the scale current, VBE is the base-emitter voltage, and Vt is the thermal voltage.
Data Source
AI summary
A self-starting bandgap reference circuit comprises a bias current source configured to provide a bias current. A bandgap core coupled to the bias current source includes a first device configured to receive the bias current and provide a first current output based on the bias current and a second device configured to receive the bias current and provide a second current output based on the bias current. A difference mirror coupled to the first device and the second device receives the first current output and the second current output and is configured to provide a difference current between the second current output and the first current output that is a proportional-to-absolute temperature current. A voltage reference output and a current reference output coupled to the difference mirror receives the proportional-to-absolute temperature current and provides a voltage reference and a current reference based on the proportional-to-absolute temperature current.