Differential Amplifier Common-Mode Feedback for Harmonic Suppression
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Solution Overview
Problem
Fully differential operational amplifiers suffer from harmonic distortion in differential output signals due to variations in the ON resistance of switches, which are not controlled to maintain a constant input voltage, leading to mismatched element devices and intermediate voltage fluctuations.
Innovation Solution
A differential amplifier design that includes a common mode detection circuit and current generation circuits to control the operating points of output terminals, using a common mode feedback circuit to ensure the intermediate voltage of input signals matches a reference voltage, thereby reducing harmonic distortion by maintaining a constant input voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a common mode feedback circuit is used to control the intermediate voltage of differential output signals to be constant, then the intermediate voltage stability is improved, but variations in input terminal voltages occur leading to harmonic distortion
Solution Approach 1:
The patent introduces a new feedback mechanism that feeds back the differential output signal to the input terminals through feedback circuits. This feedback action counteracts the voltage variations at the input terminals caused by the common mode feedback control, thereby suppressing harmonic distortion while maintaining intermediate voltage stability
Solution Approach 2:
The patent changes the operating parameters of the input differential pair by dynamically adjusting their bias conditions through the feedback mechanism. This allows the input terminals to maintain stable voltages despite the common mode feedback control, preventing the harmonic distortion that would otherwise occur
2Device complexity
If the ON resistance of switches is not controlled, then the circuit complexity is reduced, but variations in ON resistance cause mismatched element devices and intermediate voltage fluctuations
Solution Approach 1:
The feedback circuit automatically compensates for variations in switch ON resistance by adjusting the bias conditions of the input differential pair. This feedback mechanism maintains stable intermediate voltages without requiring explicit control of the switch ON resistance, thus avoiding increased circuit complexity
Solution Approach 2:
The circuit uses its own output signal to automatically correct the effects of switch ON resistance variations. The feedback mechanism self-adjusts the operating points of the input differential pair, making the system self-correcting without external intervention or additional control circuits
Data Source
AI summary
A differential amplifier is provided, in which generation of unnecessary harmonic distortion in the differential output signal is suppressed. A common mode feedback circuit increases or decreases operating points of an inverting output terminal and a non-inverting output terminal such that an intermediate voltage of voltages respectively provided to an inverting input terminal and a non-inverting input terminal is consistent with to a reference voltage. Variations in voltage at the inverting input terminal and the non-inverting input terminal are suppressed, variations in electrical properties of elements connected to the input terminals are suppressed. Therefore, it is possible to suppress generation of harmonic distortion in the output signals from the inverting output terminal and the non-inverting output terminal.