Current Mirror Stabilization via Drain Voltage Locking
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Solution Overview
Problem
Current mirror devices using MOSFETs face instability and inaccuracy in output current due to channel length modulation effects, making them susceptible to process and bias variations.
Innovation Solution
The implementation of an amplifier circuit with a specific configuration of transistors and an operational amplifier that locks drain voltages and uses feedback mechanisms to maintain consistent gate voltages, thereby reducing the impact of transistor bias current variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a prior art current mirror device uses MOSFETs with constant effective channel length in linear region, then the device structure is simple, but the output current becomes unstable and inaccurate when drain voltage increases due to channel length modulation effect
Solution Approach 1:
The patent implements feedback mechanisms using operational amplifiers that continuously monitor and adjust the gate voltages of MOSFETs. The first operational amplifier maintains equal drain voltages for the first and second MOSFETs, while the second operational amplifier does the same for the third and fourth MOSFETs. This feedback control compensates for channel length modulation effects and ensures stable output current despite drain voltage variations.
Solution Approach 2:
The patent changes the operating parameters of MOSFETs by dynamically adjusting gate voltages through operational amplifiers. Instead of relying on fixed bias conditions, the system actively controls gate voltages to maintain constant drain voltages across paired MOSFETs, thereby compensating for parameter variations caused by channel length modulation and process variations.
2Measurement precision
If the drain voltage increases causing MOSFET to enter saturation region, then the operational current becomes dependent on drain-source voltage due to channel length modulation, but maintaining constant drain voltage requires additional control circuitry
Solution Approach 1:
The patent employs feedback control through operational amplifiers that sense drain voltages and adjust gate voltages accordingly. The first operational amplifier compares drain voltages of the first and second MOSFETs and adjusts their gate voltages to maintain equality. Similarly, the second operational amplifier controls the third and fourth MOSFETs. This feedback mechanism ensures accurate output current by compensating for channel length modulation without requiring overly complex external control circuitry.
Solution Approach 2:
The operational amplifiers serve multiple functions: they act as voltage comparators, error amplifiers, and gate voltage controllers simultaneously. By integrating these functions into single operational amplifier components, the patent reduces the overall control circuitry complexity while maintaining precise output current control across multiple MOSFET pairs.
Data Source
AI summary
A current mirror device includes an input end for receiving an input signal, an output end for outputting an amplified signal of the input signal, first through third transistors, and an operational amplifier. The first transistor includes a first end coupled to first reference current and a second end coupled to a bias voltage. The control end of the second transistor is coupled to the input end. The third transistor includes a first end coupled to the output end, a second end coupled to the first end of the second transistor and a control end coupled to a reference voltage. The operational amplifier is configured to keep a first voltage and a second voltage at substantially the same level, wherein the first voltage is obtained on the first end of the first transistor and the second voltage is obtained on the first end of the second transistor. Therefore, the reference current flowing through the first transistor can be accurately amplified to a desired value and mirrored to become load current flowing through the second transistor.