Bandgap Reference Circuit Current Stability
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Solution Overview
Problem
Conventional bandgap voltage references are susceptible to temperature variations due to changes in semiconductor junction forward conduction characteristics, leading to unstable output voltage, and are dependent on transistor conduction characteristics and current gain, which can vary with physical implementation.
Innovation Solution
A bandgap reference circuit that generates a substantially constant output current using a reference generator circuit with transistors operating at predefined currents and an output circuit with a regulator forming a feedback loop to control and maintain the output current over an extended temperature range, reducing variance based on physical process characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap voltage reference circuits are used, then a stable reference voltage can be obtained, but the output voltage is susceptible to temperature variations and changes in transistor conduction characteristics
Solution Approach 1:
The patent transforms the bandgap reference from a voltage output to a current output. The reference generator produces a current that is substantially independent of temperature and process variations. This current can then be converted to a voltage if needed, but the current itself serves as the primary reference, eliminating the temperature coefficient issues inherent in voltage-based bandgap references.
Solution Approach 2:
The patent replaces the traditional voltage-based bandgap reference mechanism with a current-based reference mechanism. Instead of relying on voltage summation (VBE + VTHERMAL) to achieve temperature compensation, the invention uses current mirrors and transistors operating in specific regions to generate a temperature-stable current reference.
2Reliability
If conventional bandgap voltage reference circuits are used, then a reference voltage can be generated, but the output is dependent on transistor conduction characteristics and current gain which vary with physical implementation
Solution Approach 1:
The patent changes the reference output parameter from voltage to current. The current reference generated is substantially independent of transistor beta (current gain) and other conduction characteristics that vary with manufacturing processes. This is achieved through careful design of the reference generator using transistors operating in specific regions and current mirror configurations that cancel out process variations.
3Temperature
If transistor-based bandgap reference circuits are used, then temperature compensation can be achieved, but the circuit complexity increases
Solution Approach 1:
The patent replaces the complex voltage-based temperature compensation mechanism with a simpler current-based approach. Instead of summing VBE and VTHERMAL voltages with precise resistor ratios, the invention uses current mirrors and transistor configurations that inherently provide temperature compensation through their operating characteristics, reducing circuit 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 robust and stable output current that is less dependent on temperature and physical implementation variations, maintaining consistency across a wide temperature range and minimizing the impact of process-related changes.
Implementation Method 1
The basic principle behind the bandgap reference is the well-known voltage drop associated with certain semiconductor junctions. For example, a silicon p-n junction such as the emitter-base junction bipolar transistor may have a forward conduction characteristic (i.e., voltage drop) of about 0.6 volts.
Implementation Method 2
Improved bandgap voltage references have been proposed which employ various compensation schemes that attempt to normalize output voltage over a wide temperature range. Such bandgap reference circuits are transistor-based and operate on the principle of compensating the negative temperature coefficient of a base-emitter voltage (VBE) of a bipolar transistor with the positive temperature coefficient of the thermal voltage
Implementation Method 3
an output circuit coupled to the reference generator circuit that provides the substantially constant output current proportional to the second predefined current
Data Source
AI summary
Circuits and methods that improve the performance of reference circuits are provided. A reference generator circuit maintains a substantially constant output current over an extended temperature for use as a reference. Output current fluctuations caused by a poorly specified power source or process variations are minimized or eliminated.