Bandgap Voltage Reference Circuit Common-Mode Control
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Solution Overview
Problem
Bandgap voltage reference circuits face challenges with extreme variability of common-mode voltage at operational amplifier input terminals, particularly in low supply voltage conditions, leading to incorrect amplifier operation and increased production costs due to the need for additional lithography masks.
Innovation Solution
A bandgap voltage reference circuit with a control circuit that adjusts the common-mode voltage using capacitive means and biasing, ensuring operational amplifier input stage transistors operate in saturation, even at low supply voltages, by generating a common-mode voltage calibrated to manufacturing parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the common-mode voltage is allowed to vary with temperature in a bandgap circuit, then the circuit can operate with standard supply voltages, but the operational amplifier transistors are forced into triode operation region at low supply voltages causing incorrect operation
Solution Approach 1:
The patent applies dynamics by making the common-mode voltage adjustable rather than fixed. The biasing circuit dynamically adapts the common-mode voltage level according to the supply voltage conditions, allowing the operational amplifier to maintain correct operation across different supply voltages and temperatures.
Solution Approach 2:
The patent changes the common-mode voltage parameter to resolve the contradiction. By adjusting the common-mode voltage through the biasing circuit, the patent ensures that transistors operate in the saturation region even when supply voltage varies with temperature, preventing triode region operation.
2Measurement precision
If n-channel MOS transistors are used in the operational amplifier input stage, then the circuit can achieve high gain and good noise rejection, but the transistors are forced into triode operation at low supply voltages due to common-mode voltage excursions
Solution Approach 1:
The patent changes the common-mode voltage parameter to keep n-channel MOS transistors in saturation region. By adjusting the common-mode voltage through the biasing circuit, the patent ensures adequate voltage headroom for the transistors to operate correctly even at low supply voltages, maintaining both noise rejection and reliability.
Solution Approach 2:
The biasing circuit acts as an intermediary between the supply voltage and the operational amplifier. It mediates the voltage relationship by providing appropriate common-mode voltage levels, ensuring that the transistors receive sufficient voltage headroom to operate in saturation despite variations in supply voltage.
3Loss of energy
If the supply voltage is reduced to minimize leakage currents during stand-by phases, then power consumption is reduced, but the common-mode voltage excursions become too large forcing transistors into triode operation
Solution Approach 1:
The patent applies dynamics by making the common-mode voltage adaptable to different supply voltage conditions. During stand-by phases with reduced supply voltage, the biasing circuit dynamically adjusts the common-mode voltage to maintain adequate headroom, preventing triode operation while allowing low-power operation.
Solution Approach 2:
The patent changes the common-mode voltage parameter in response to supply voltage changes. When supply voltage is reduced to minimize leakage, the biasing circuit相应地 adjusts the common-mode voltage to prevent excessive excursions that would force transistors into triode region, enabling low-power operation without sacrificing reliability.
Data Source
AI summary
A bandgap voltage reference circuit for generating a bandgap voltage reference. An embodiment comprises a current generator controlled by a first driving voltage for generating a first current depending on the driving voltage, and a first reference circuit element coupled to the controlled current generator for receiving the first current and generating a first reference voltage in response to the first current. The circuit further comprises a second reference circuit element for receiving a second current corresponding to the first current; said second reference circuit element is adapted to generate a second reference voltage in response to the second current. The circuit further comprises an operational amplifier having a first input coupled to the first circuit element and a second input coupled to the second reference circuit element. The circuit also comprises a control circuit comprising first capacitive element and second capacitive element.