Amplifier Bias Reference Circuit for Stable Small-Signal Transconductance
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Solution Overview
Problem
Existing reference sources for integrated circuits do not adequately control the predictability of small-signal gain due to factors affecting current and gain differently, leading to unpredictable variations.
Innovation Solution
A circuit with one or more reference transistors and a feedback loop that regulates control voltage to achieve a predetermined differential transconductance, using a small voltage offset to monitor and control the differential transconductance, ensuring a linear difference in main current proportional to the voltage offset, thereby stabilizing the small-signal gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference source provides a controlled reference voltage to an amplifier, then the bias setting is stabilized, but the small-signal gain still varies unpredictably due to factors affecting current and gain differently
Solution Approach 1:
The patent implements a feedback mechanism where the reference source monitors the actual small-signal gain of the amplifier and adjusts the bias current accordingly. This closed-loop control ensures that the small-signal gain remains predictable and stable, directly resolving the contradiction by using feedback to compensate for factors that cause gain variation.
Solution Approach 2:
The reference source dynamically adjusts the bias current parameter based on monitored conditions to maintain predictable small-signal gain. By changing the bias current in response to detected variations, the system compensates for factors affecting current and gain differently, ensuring reliable gain control while maintaining bias stability.
2Stability of the object's composition
If the drain current is adjusted to balance transfer size ratio and gate-source voltage offset effects, then the reference voltage becomes stable, but the small-signal gain control remains insufficient
Solution Approach 1:
The system uses feedback to continuously monitor the small-signal gain and adjust the bias current accordingly. This allows the reference voltage to remain stable while the feedback mechanism compensates for any variations in small-signal gain, achieving both stability and precise control simultaneously.
Solution Approach 2:
The reference source transitions from a static bias setting to a dynamic control mechanism that continuously adjusts the bias current based on real-time monitoring of small-signal gain. This dynamic adjustment ensures that the system maintains predictable gain control while preserving reference voltage stability through adaptive compensation.
Data Source
AI summary
A circuit has a reference source (12) for supplying a bias signal to set a small signal transconductance of an amplifier transistor in an amplifier (10) to a predetermined value. The reference source has at least one reference transistor (120a-b, 30). A feedback circuit (128, 129, 38) has an input coupled to the main current channel of the reference transistor or reference transistors (120a-b, 30) and an output coupled to the control electrode of the reference transistor or reference transistors (120a-b, 30). The feedback circuit controls a control voltage at the control electrode, so as to equalize an offset current and a difference between main currents flowing through the current channel of the reference transistor or reference transistors (120a-b, 30), obtained with and without a small voltage offset added to the control voltage. The main currents flowing with and without a small voltage offset may be obtained by using a first and second reference transistor (122a,b), matching each other and an offset voltage source (126) coupled between the control electrodes of the first and second reference transistor (122a,b), to apply the small voltage offset between their control electrodes.