Input Tracking Current Mirror for Differential Amplifier
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Solution Overview
Problem
Conventional mirror bias systems for differential amplifiers fail to maintain current matching between the input and output legs when common mode voltage changes or differential voltages are applied, due to finite output resistances and the fixed biasing of cascode devices.
Innovation Solution
An input tracking current mirror system with a differential amplifier and a tracking circuit featuring multiple transconductance components that replicate the voltage on the output leg to the input leg, ensuring current matching across varying common mode and differential voltages, using feedback loops and biasing devices to enhance headroom and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional current mirror with fixed bias is used, then the circuit structure is simple, but the current matching between input and output legs deteriorates when common mode voltage changes or differential voltages are applied
Solution Approach 1:
The patent applies dynamics by making the bias voltage dynamic rather than fixed. The bias voltage is generated through a tracking circuit that dynamically adjusts to follow changes in common mode voltage and differential voltage, ensuring the current mirror maintains accuracy under varying operating conditions.
Solution Approach 2:
The patent implements feedback through a tracking circuit that monitors the voltage at the output leg and feeds back information to adjust the bias voltage at the input leg. This feedback mechanism ensures that the current mirror compensates for voltage changes and maintains precise current matching.
2Manufacturing precision
If a cascode device with fixed VBIAS is added to improve current matching, then the current matching improves at a fixed common mode voltage, but the system loses adaptability when common mode voltage changes
Solution Approach 1:
The patent transforms the static fixed VBIAS into a dynamic tracking voltage. The tracking circuit dynamically adjusts the bias voltage to follow changes in common mode voltage and differential voltage, providing both precise current matching and adaptability across a wide voltage range.
Solution Approach 2:
The patent changes the parameter of bias voltage from a fixed value to a variable that tracks with operating conditions. By making the bias voltage a function of common mode voltage and differential voltage, the system maintains current matching accuracy across varying voltage conditions.
3Measurement precision
If the tracking circuit uses multiple transconductance components to follow voltage changes, then the voltage tracking accuracy improves, but the device complexity increases
Solution Approach 1:
The patent uses copying by creating a simplified replica of the differential amplifier circuit specifically for voltage tracking. The tracking circuit copies the essential transconductance characteristics to follow voltage changes, achieving accurate tracking with a dedicated simplified sub-circuit rather than complicating the main amplifier.
Data Source
AI summary
An input tracking current mirror for a differential amplifier system includes a current mirror having an input leg and an output leg, a differential amplifier including a first set of at least two transconductance components, each having at least one input terminal for receiving input signals, the first set of at least two transconductance components having a first common node connected to the output leg which has a first voltage that is a function of the input signals, and a tracking circuit including a second set of at least two transconductance components each having at least one input terminal for receiving the input signals, the second set of at least two transconductance components, having a second common node connected to the input leg which has a second voltage that is a function of the input signals, the tracking circuit driving the second voltage on the input leg to track the first voltage on the output leg with variations in the input signals.