Bandgap Voltage Reference Circuit With Current Mirror Loop Feedback
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Solution Overview
Problem
Bandgap voltage reference circuits are susceptible to noise from operational amplifiers, leading to significant changes in output voltage due to input-referred noise, with a substantial gain that affects the stability of the reference voltage.
Innovation Solution
The implementation of a current mirror loop and a specific configuration of bipolar junction transistors and resistors within the bandgap voltage reference circuit, which maintains equal Vbe voltages across transistors and adjusts the voltage across resistors to minimize the impact of operational amplifier noise, achieving a gain of approximately unity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bandgap voltage reference circuit is used, then the output reference voltage is generally constant despite fluctuations in power supply, load current, and temperature, but the circuit is susceptible to noise from operational amplifiers leading to significant changes in output voltage due to input-referred noise with substantial gain
Solution Approach 1:
The patent introduces a current mirror loop as an intermediary mechanism between the operational amplifier and the voltage reference output. This current mirror loop acts as a mediator that decouples the noise gain from the voltage output, allowing the operational amplifier to operate without its noise being amplified significantly at the output. The current mirror configuration ensures that current variations due to noise are mirrored and canceled, preventing noise propagation to the voltage reference output.
Solution Approach 2:
The patent implements a feedback mechanism through the operational amplifier that monitors the voltage across the resistors and adjusts the current through the bipolar junction transistors to maintain equal Vbe voltages. This feedback loop compensates for noise-induced variations by dynamically adjusting operating points, thereby reducing the impact of operational amplifier noise on the reference voltage output while maintaining temperature compensation functionality.
2Temperature
If the circuit uses bipolar junction transistors with temperature compensation, then the output voltage remains stable across temperature changes, but the configuration amplifies operational amplifier noise through substantial gain
Solution Approach 1:
The patent segments the voltage reference circuit into distinct functional blocks: a temperature compensation network using bipolar junction transistors, a noise-sensitive operational amplifier stage, and a current mirror loop. By segmenting the circuit, the temperature compensation function can be maintained through the transistor network while the current mirror segment isolates the operational amplifier noise from the final voltage output, allowing both temperature stability and noise reduction to coexist.
Solution Approach 2:
The current mirror loop serves as an intermediary between the temperature compensation transistors and the operational amplifier. It allows the temperature compensation mechanism to function independently while preventing the operational amplifier noise from being amplified and affecting the precision of the reference voltage output, thus resolving the contradiction between temperature stability and measurement precision.
3Reliability
If the operational amplifier gain is increased to improve voltage regulation, then the reference voltage becomes more stable against supply fluctuations, but the impact of input-referred noise on output voltage increases significantly
Solution Approach 1:
The current mirror loop acts as a noise-isolating intermediary that allows the operational amplifier to maintain high gain for good voltage regulation while preventing this gain from amplifying input-referred noise at the voltage output. The current mirror configuration ensures that noise currents are mirrored and canceled before converting to voltage, decoupling the regulation performance from noise amplification.
Solution Approach 2:
The patent converts the potentially harmful effect of operational amplifier noise into a beneficial outcome by using the current mirror loop to mirror and cancel noise currents. The high gain of the operational amplifier, which would normally amplify noise, is instead used to maintain precise voltage regulation while the current mirror configuration ensures that noise does not propagate to the output, effectively converting the noise issue into an opportunity for improved regulation without noise penalties.
Data Source
AI summary
A bandgap reference circuit includes a first diode-coupled transistor having a first control terminal and first and second current terminals and a second transistor having a second control terminal and third and fourth current terminals. The second control terminal is coupled to the first control terminal. A third transistor have a third control terminal and fifth and sixth current terminals. A fourth diode-coupled transistor has a fourth control terminal and seventh and eighth current terminals. The fourth control terminal is coupled to the third control terminal. An operational amplifier has a first input, a second input, and an output. The output is coupled to the first current terminal. A first resistor is coupled between the output and the third current terminal. A second resistor is coupled between the sixth and eighth current terminals.