Differential Amplifier Calibration for Resistor Ratio Linearity
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Solution Overview
Problem
Non-linearity in amplifiers causes undesirable distortions in differential output signals due to mismatches in resistance ratios of feedback and input resistors, leading to harmonic components in the output signal.
Innovation Solution
A calibration mechanism is implemented to equalize the ratios of feedback resistances to input resistances by using T-networks and digital control signals to adjust the effective resistances, minimizing mismatches and reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If resistance ratios of feedback and input resistors are not equalized, then the amplifier can operate with simple fixed resistor values, but non-linearity and distortion occur in the differential output signal
Solution Approach 1:
The patent applies preliminary action by performing resistance ratio calibration during the manufacturing process before the amplifier is delivered to the customer. The calibration mechanism pre-adjusts the effective resistance ratios of feedback and input resistors to be equal, storing these calibrated values in memory. This eliminates the need for field calibration and ensures high linearity performance is achieved without requiring complex user-adjustable components.
Solution Approach 2:
The patent changes the resistance parameters dynamically through the calibration mechanism, which adjusts the effective resistance values of feedback and input resistors. By varying these resistance parameters during calibration and storing the optimal values, the system achieves precise resistance ratio matching that minimizes distortion while maintaining operational simplicity during normal use.
2Reliability
If resistance ratios are precisely equalized through calibration, then linearity is improved and distortion is reduced, but the calibration process adds manufacturing complexity
Solution Approach 1:
The patent implements feedback by measuring the actual resistance ratios during calibration and using this information to adjust the effective resistance values. The calibration mechanism continuously monitors and adjusts the resistance parameters until the desired linearity performance is achieved, then stores these calibrated values for use during normal operation, ensuring high reliability without requiring complex manual adjustment procedures.
Solution Approach 2:
The calibration mechanism performs self-service by automatically equalizing the resistance ratios without requiring manual intervention during normal operation. The system self-calibrates during manufacturing, stores the optimal resistance values in memory, and automatically applies these calibrated parameters during operation, thereby achieving high linearity while simplifying the ease of manufacture for end users.
3Ease of manufacture
If fixed resistor values are used without calibration, then the device is simpler to manufacture, but harmonic distortion occurs in the output signal
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the resistance ratios during manufacturing before the amplifier enters service. The calibration mechanism adjusts the effective resistance values and stores these calibrated parameters in memory, ensuring that the amplifier operates with equalized resistance ratios from the start. This eliminates signal distortion while maintaining the simplicity of using fixed resistor values during normal operation.
Solution Approach 2:
The calibration mechanism acts as an intermediary between the fixed resistors and the amplifier operation. It measures and adjusts the effective resistance ratios, then stores these calibrated values to mediate between the simplicity of fixed resistors and the requirement for precise resistance matching, thereby eliminating distortion without requiring complex adjustable resistor networks during normal use.
Data Source
AI summary
A fully differential amplifier includes a first feedback resistance, a second feedback resistance, a first input resistance and a second input resistance. A first ratio of the first feedback resistance to the first input resistance is equalized with that of a reference ratio of a pair of reference resistances. Similarly a second ratio of the second feedback resistance to the second input resistance is also equalized with that of the reference ratio. Such equalization operations may be performed during a calibration phase prior to normal operation of the fully differential amplifier. Accordingly, when a common mode voltage present on each of the first output terminal and the second output terminal varies during normal operation, contribution of an erroneous differential signal component across the pair of differential output terminals is prevented.