Bandgap Reference Circuit for Low Voltage Stability
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Solution Overview
Problem
Conventional bandgap reference circuits struggle to provide a stable reference voltage with a zero temperature coefficient at various voltage levels, limiting their applicability in different integrated circuits.
Innovation Solution
A bandgap reference circuit comprising current sources, amplifiers, bipolar transistors, and resistors, with feedback mechanisms to generate stable reference voltages and currents, allowing adjustment of resistor values to achieve desired temperature coefficients and voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional bandgap reference circuit is used to generate a stable reference voltage with zero temperature coefficient, then the voltage stability is improved, but the voltage level is fixed at around 1.25V which limits adaptability to different voltage requirements
Solution Approach 1:
The reference voltage generation is divided into two independent stages: first, a conventional bandgap circuit generates a stable 1.25V reference voltage with zero temperature coefficient; second, a separate voltage divider network (R3, R4) converts this reference to the desired output voltage level. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between stability and adaptability.
Solution Approach 2:
A buffer amplifier (operational amplifier OP) is introduced as an intermediary between the bandgap reference circuit and the voltage divider network. This buffer isolates the stable reference voltage source from the loading effects of the voltage divider, ensuring that the temperature coefficient remains zero while enabling flexible voltage level adjustment through the divider ratio.
2Adaptability or versatility
If the output voltage level is reduced to meet low-voltage application requirements, then the adaptability is improved, but maintaining a zero temperature coefficient becomes more difficult
Solution Approach 1:
The temperature compensation function is segmented and kept entirely within the bandgap reference circuit portion, while the voltage level adjustment is handled separately by the voltage divider. This ensures that the zero temperature coefficient property is preserved in the reference generation stage regardless of the output voltage level selected by the divider.
Solution Approach 2:
The buffer amplifier provides voltage feedback to maintain the virtual ground at its inverting input, ensuring that the voltage divider operates without loading the bandgap reference circuit. This feedback mechanism guarantees that the output voltage follows the divider ratio exactly while maintaining the zero temperature coefficient characteristic.
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 stable output currents and voltages with adjustable temperature coefficients, enabling operation across a wide voltage range from 0V to VDD-VSD, M4, and precise voltage levels, including lower voltage levels like less than 0.6V, enhancing its applicability in diverse integrated circuit applications.
Implementation Method 1
VT is the thermal voltage at room temperature
Data Source
AI summary
A bandgap reference circuit incorporates first, second, and third current sources, first and second amplifiers, first and second bipolar transistors, a feedback device, a first resistor, and a second resistor. The first resistor is coupled between one input of the second amplifier and the base of the first bipolar transistor. The second resistor is coupled between the base of the first bipolar transistor and the base of the second bipolar transistor. The first and second amplifies and the first to third current sources constitute negative feedback loops which force the voltages at the inputs of the amplifiers to be substantially equal.