Dual-Input Differential Feedback for Ground Bounce Noise Cancelation
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Solution Overview
Problem
Differential feedback circuits face challenges in effectively canceling noise signals, particularly in switched mode power supply (SMPS) systems, where noise can lead to output errors and instability due to ground bounce and parasitic inductance, requiring additional filtering that reduces bandwidth or increases circuit complexity.
Innovation Solution
A dual input differential pair configuration with a primary and secondary input pair, where the secondary pair is inverted relative to the primary pair, and a low pass filter is used to connect the feedback voltage to the secondary pair, allowing the noise to be canceled at the output of the error amplifier, thereby reducing noise impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-input differential amplifier is used for feedback, then circuit complexity is low, but noise cancellation capability is insufficient leading to output errors and instability
Solution Approach 1:
The differential amplifier input stage is segmented into two separate input pairs: a primary input pair for standard feedback signals and a secondary input pair dedicated to noise cancellation. This segmentation allows independent optimization of each input path, enabling effective noise rejection while maintaining circuit functionality.
Solution Approach 2:
A secondary input pair acts as an intermediary mechanism that receives noise signals through a low-pass filter and injects them with inverted polarity into the differential amplifier. This intermediary path enables noise cancellation without disrupting the primary feedback loop operation.
2Reliability
If additional filtering is added to reduce noise impact, then noise cancellation improves, but bandwidth is reduced and circuit complexity increases
Solution Approach 1:
The filtering function is segmented and dedicated solely to the secondary input pair, leaving the primary input path unaffected. This allows aggressive noise filtering in the secondary path without impacting the bandwidth of the main feedback loop, as each path operates independently.
Solution Approach 2:
The low-pass filter serves as an intermediary element in the secondary input path, selectively attenuating noise frequencies before they reach the differential amplifier. This intermediary filtering approach removes noise without requiring bandwidth reduction in the primary feedback path.
3Reliability
If noise cancellation circuitry is added, then output stability improves, but circuit footprint increases
Solution Approach 1:
The noise cancellation functionality is merged with the existing differential amplifier structure by adding a secondary input pair that shares the same operational amplifier core. This integration approach achieves noise cancellation without requiring separate dedicated circuitry, thereby minimizing additional footprint.
Solution Approach 2:
The differential amplifier is designed with universal input capability to accept both primary feedback signals and secondary noise cancellation signals through its two input pairs. This multi-functionality allows a single circuit element to serve multiple purposes, reducing the need for additional specialized components.
Data Source
AI summary
A differential feedback circuit with an active noise cancelation technique using a dual input differential pair. In the differential feedback circuit, a feedback voltage and a reference voltage connect to a primary input pair. Sensed noise at the inputs is put to a secondary input pair of the differential amplifier, which is inverted with respect to the primary input pair. In other words, the reference voltage, which may be subject to noise, connects directly to one terminal of the secondary input pair and through a low-pass filter to another terminal of the secondary input pair so that the noise, which may be coupled to the differential feedback circuit, cancels at the output of the differential feedback circuit.