Current Mirror Circuit Compensating Supply Voltage Variations
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Solution Overview
Problem
Current mirror circuits in RF and microwave power amplifiers face challenges in accurately mirroring input current due to variations in supply voltage, ambient temperature, and manufacturing variations, particularly exacerbated by the Early voltage effect, which causes shifts in transistor bias points and errors in current ratios.
Innovation Solution
The proposed electronic circuit includes a first and second current mirror circuit, along with a current control transistor and an error transistor, where the second current mirror circuit compensates for supply voltage variations by drawing a compensating current from the first current mirror circuit, using resistors to control the magnitude of this compensating current, thereby maintaining a stable bias point and minimizing current variations through a current source configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a standard current mirror circuit is used, then the circuit structure is simple, but the output current cannot accurately mirror the input current due to supply voltage variations and the Early voltage effect
Solution Approach 1:
The patent introduces a feedback mechanism where a portion of the output current is fed back to the input side through a feedback transistor. This feedback loop automatically adjusts the base current of the output transistor to compensate for variations caused by supply voltage changes and the Early voltage effect, thereby improving current mirroring accuracy without significantly increasing circuit complexity
Solution Approach 2:
The patent employs parameter changes by introducing adjustable resistors and transistors that allow dynamic adjustment of the current mirror ratio. By changing the operating parameters (such as base-emitter voltage and collector current) of the mirror transistors, the circuit can compensate for the Early voltage effect and maintain accurate current mirroring across different supply voltage conditions
2Power
If the supply voltage increases, then the current gain increases due to the Early voltage effect, but the current ratio across mirroring transistors becomes erroneous
Solution Approach 1:
The feedback transistor monitors the output current and adjusts the base current accordingly. When supply voltage increases and causes erroneous current ratio due to the Early voltage effect, the feedback mechanism detects this deviation and automatically corrects it by adjusting the base current, thus maintaining accurate current ratio despite changes in current gain
Solution Approach 2:
The circuit applies preliminary anti-action by pre-compensating for the Early voltage effect through the feedback network. Before the erroneous current ratio fully develops, the feedback mechanism anticipates the deviation and applies a counteracting adjustment to the base current, preventing the error from occurring in the first place
3Measurement precision
If compensation for supply voltage variations is added, then current mirroring accuracy improves, but the device complexity increases
Solution Approach 1:
The feedback mechanism provides automatic compensation for supply voltage variations using minimal additional components. By utilizing the existing output current and a feedback transistor, the circuit achieves compensation without requiring complex external control circuits or multiple additional active devices
Solution Approach 2:
The feedback transistor serves multiple functions: it acts as both a compensation element for supply voltage variations and as part of the current mirroring structure itself. This multi-functionality allows the circuit to achieve compensation while minimizing the increase in overall device complexity
Data Source
AI summary
An electronic current mirror circuit particularly suitable for use in radio frequency (RF) and microwave power amplifiers. The electronic circuit includes a first current mirror circuit and a second current mirror circuit. The first current mirror circuit includes a first input circuit path and a first output circuit path, the first input circuit path is operated at a first supply voltage and the first output circuit path is operated at a second supply voltage. The second current mirror circuit includes a second input circuit path and a second output circuit path, the second input circuit path is operated at the second supply voltage, and the second output circuit path is connected to the first input circuit path so that variations in a current through the first output circuit path are compensated by a current in the second output circuit path.