Amplifier Bias Circuit for Constant Gain and Stable Output Voltage
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Solution Overview
Problem
The gain of amplifier circuits in semiconductor devices is not stable due to independent variations in transconductance and resistance, leading to significant fluctuations in output direct current voltage and deterioration of signal distortion characteristics.
Innovation Solution
A semiconductor device with a gain control circuit, a first circuit with a constant gain, and a bias circuit that generates a differential current proportionate to the drain current of a transistor and inversely proportionate to the load resistance, stabilizing the output voltage by connecting the bias circuit to the output node of the first circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a Gm compensation bias circuit is used to make the gain constant, then the gain stability is improved, but the output direct current voltage varies greatly due to drain current variation
Solution Approach 1:
The patent introduces a bias circuit as an intermediary component that generates a compensation current to offset the variation in drain current. This bias circuit acts as a mediator between the Gm compensation bias circuit and the output node, providing an additional control mechanism that stabilizes the output voltage without affecting the gain constant property.
Solution Approach 2:
The patent implements a feedback mechanism where the bias circuit monitors the drain current variation and generates a compensating current in response. This feedback loop detects the output voltage variation caused by drain current changes and actively counteracts it, maintaining stable output voltage while preserving the constant gain characteristic.
2Stability of the object's composition
If the drain current is increased to compensate for transconductance variation, then the gain stability is improved, but the output signal distortion deteriorates due to voltage limitation
Solution Approach 1:
The patent applies the counterweight principle by introducing a bias current that acts as an opposing force to the harmful effect of drain current variation. The bias circuit generates a current that counterbalances the variations, preventing both gain instability and output voltage swing limitations that cause signal distortion.
Solution Approach 2:
The patent changes the operating parameters of the circuit by dynamically adjusting the bias current generated by the bias circuit. This parameter adjustment allows the circuit to maintain optimal operating conditions across different transconductance values, preventing output voltage from reaching saturation levels that would cause signal distortion while maintaining constant gain.
Data Source
AI summary
A semiconductor device including: a gain control circuit; a first circuit which is controlled a gain to be constant by the gain control circuit; and a bias circuit connected to the first circuit, wherein the first circuit including a first transistor; and a load resistance, an amplification factor or an attenuation factor of the first circuit is proportionate to a product of a transconductance of the first transistor and a resistance value of the load resistance, and a voltage applied to the load resistance is set as an output of the semiconductor device, the bias circuit generates and outputs a differential current of a current that is proportionate to a drain current flowing into the first transistor and a current that is inversely proportionate to the load resistance value, and an output of the bias circuit is connected to an output node of the first circuit.