Reversed Bandgap Voltage Reference Circuit for Low-Voltage Operation
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Solution Overview
Problem
Existing bandgap voltage reference circuits struggle to provide precise and low-noise reference voltages when operating from power supply voltages less than 1 volt, often requiring complex current source circuitry and suffering from noise errors due to current mirror transistors.
Innovation Solution
The proposed reversed bandgap voltage reference circuit uses a configuration with resistors and transistors, where the collector currents of two transistors are forced to be equal, and the base-emitter voltages are manipulated using operational amplifiers to achieve a stable and accurate output voltage, avoiding transistor saturation and complex current source requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional bandgap voltage reference circuits are used to achieve stable reference voltage, then temperature coefficient is less than 50 ppm/degrees Centigrade, but the circuit cannot operate from supply voltages below approximately 1.3V
Solution Approach 1:
The patent inverts the traditional bandgap approach by using a sub-bandgap voltage (approximately 0.6V) as the reference output. Instead of generating a voltage above the supply threshold, the circuit uses operational amplifiers and transistor configurations to create a stable reference voltage that is one-quarter of the supply voltage, enabling operation from supply voltages as low as 0.6V while maintaining temperature stability through feedback control
2Adaptability or versatility
If current mirror transistors are used in the feedback loop to generate reference voltage, then the circuit can operate at low supply voltages, but large amounts of 1/f noise is generated causing large noise errors in the output voltage
Solution Approach 1:
The patent removes current mirror transistors from the feedback loop entirely, replacing them with operational amplifier-based voltage control. The feedback mechanism uses op-amps to directly control transistor biasing without requiring current mirrors, thereby extracting the noise-generating element while preserving the low-voltage operation capability through alternative current control paths
3Object-generated harmful factors
If external filter capacitance is increased to limit noise bandwidth, then noise errors in output voltage are reduced, but device complexity and area increase
Solution Approach 1:
The patent converts the potential harm of noise by using the transistor base-emitter junctions as inherent low-pass filters. The junction capacitance and resistance form natural RC filters that suppress high-frequency noise without requiring external filter capacitors, thereby turning the transistor's parasitic elements into beneficial noise-filtering components
Data Source
AI summary
A circuit producing a reversed bandgap reference voltage circuit VRBG includes first and second resistors coupled as a voltage divider between ground and a first conductor, a base of a first transistor being coupled to the voltage divider to produce a first voltage VBE1(1+1/M) between the first conductor and ground, M being a ratio of the resistances of the first and second resistors. A third resistor is coupled between a base of the second transistor and ground to produce a second voltage VBE2+VRBGP between the second conductor and ground. First circuitry forces the collector current of the first transistor to be equal to the collector current of the second transistor, and second circuitry forces the first voltage VBE1(1+1/M) to be equal the second voltage VBE2+VRBGP. One of the first circuitry and second circuitry includes an operational amplifier coupled to effectuate the forcing.