Virtual-Ground Transconductance Amplifier for Low-Distortion AC Current
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Solution Overview
Problem
Existing transconductance amplifiers face limitations in delivering current to grounded loads due to input range and output range restrictions, requiring additional circuitry for DC bias and introducing distortion, especially at high frequencies.
Innovation Solution
A low distortion transconductance amplifier design utilizing a virtual ground input stage and a pair of current mirrors, which eliminates the need for DC bias voltage by using a bias current source and current mirrors to deliver current to grounded loads, reducing distortion and improving noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional transconductance amplifier uses DC bias voltage to deliver current to grounded loads, then the amplifier can operate at high frequencies, but distortion increases and additional zeroing circuitry is required
Solution Approach 1:
The patent introduces a virtual ground input stage as an intermediary that converts the input voltage to a current that flows through a resistor to ground. This virtual ground mechanism acts as a mediator between the input voltage source and the grounded load, enabling the amplifier to deliver current to grounded loads without requiring DC bias voltage, thereby reducing distortion while maintaining high-frequency operation
Solution Approach 2:
The patent changes the biasing parameter from voltage-based DC bias to current-based biasing through the virtual ground stage. By using a resistor connected to ground and generating a corresponding current, the amplifier operates with different electrical parameters that eliminate the need for additional zeroing circuitry and reduce distortion at high frequencies
2Ease of operation
If a conventional transconductance amplifier uses DC bias voltage, then current can be delivered to grounded loads, but additional zeroing circuitry is required
Solution Approach 1:
The virtual ground input stage serves as an intermediary that directly enables current delivery to grounded loads without requiring additional zeroing circuitry. The virtual ground mechanism mediates between the input voltage and the grounded load, simplifying the overall circuit architecture while maintaining the ability to drive grounded loads effectively
Solution Approach 2:
The patent extracts and eliminates the need for additional zeroing circuitry by using the virtual ground input stage. The virtual ground mechanism inherently handles the biasing requirements, allowing the amplifier to deliver current to grounded loads without the complexity of separate zeroing circuits
Data Source
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AI summary
A low distortion transconductance amplifier (121) provides current to a grounded load (RL) using a virtual ground input stage (U1, Q1, Q2), a pair of current mirrors (108a, 108b), and a bias current source (Ib). The virtual ground input stage (U1, Q1, Q2) may include transistors arranged as a Darlington pair (Q1, Q2). The low distortion transconductance amplifier (121) can function as a voltage-controlled AC current source that is operable at high frequencies.