Amplifier Bias Circuit Distortion Cancellation Using Impedance Matching
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Solution Overview
Problem
Amplifier circuits face signal distortion due to non-linear output characteristics of bias current sources, which existing techniques attempt to address through complex circuit additions or performance reductions.
Innovation Solution
Incorporating an impedance device into the feedback path of a diode-connected transistor to sample and cancel signal distortion caused by non-linear output impedance, without adding complexity or reducing frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adjustable gain with negative feedback is incorporated before the node with non-linear characteristic, then signal distortion is reduced, but circuit complexity increases and frequency performance deteriorates
Solution Approach 1:
The patent extracts the distortion-canceling function from a complex feedback circuit and implements it through a simplified current mirror configuration. The bias circuit generates a mirror image of the distortion signal and subtracts it from the output, achieving distortion reduction without requiring complex adjustable gain stages or extensive feedback networks.
Solution Approach 2:
The patent changes the operating parameters of the bias current source by adjusting its output impedance characteristics. By modifying the bias circuit configuration and component values, the distortion signal is transformed into a form that can be effectively mirrored and canceled, improving signal fidelity without adding circuit complexity.
2Reliability
If degeneration of amplifier's internal current sources is applied, then signal distortion is reduced, but impedance of current sources is not improved
Solution Approach 1:
The patent implements a feedback mechanism where the bias circuit continuously monitors the distortion signal and generates a compensating current through the current mirror. This feedback loop adjusts the output to cancel distortion effects, effectively improving signal fidelity while maintaining the original current source impedance characteristics.
3Ease of operation
If bias circuits with non-linear output characteristics are used, then amplifier functionality is achieved, but signal distortion is introduced
Solution Approach 1:
The patent converts the harmful non-linear output characteristics of the bias current source into a beneficial feature. By using the same non-linear bias circuit to generate both the operating current and the distortion compensation signal, the inherent non-linearity is transformed into a mechanism for distortion cancellation through the current mirror configuration.
Data Source
AI summary
A device to reduce distortion in an amplifier includes an input transistor configured to generate a voltage based on an input signal. The device further includes a diode connected transistor that is configured to sink the current. The diode connected transistor includes an output terminal, and a control terminal, where the output terminal is coupled to a control terminal. The device further includes a current source circuit that coupled to the control terminal. The device additionally includes an impedance element that coupled to the output terminal at a first node and to the control terminal and the current source circuit at a second node.