Isolated Feedback Output Stage for Fast Saturation Recovery
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Solution Overview
Problem
Regulated output circuits face challenges in recovering quickly from saturation conditions due to slew rate limitations, especially when external circuits pull down on the bus, leading to transients and reduced noise margins, particularly in unidirectional output stages.
Innovation Solution
The implementation of an isolation feedback loop with a source-follower output stage and replica biasing configuration allows for rapid response to external load transients, isolating voltage and current feedback loops to prevent saturation, enabling faster and more robust recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional regulated output circuits are used with feedback from the output node, then voltage regulation is maintained, but the circuit experiences saturation and slow recovery due to slew rate limitations when external circuits pull down on the bus
Solution Approach 1:
The feedback path is segmented into two separate loops: a voltage feedback loop that senses voltage at an intermediate node (before the output stage) and a current feedback loop that senses current at the output node. This segmentation prevents the voltage feedback loop from saturating when the output is pulled down externally, while the current feedback loop handles the actual output regulation.
Solution Approach 2:
An intermediate sensing node is introduced between the output stage and the external bus. The voltage feedback is taken from this intermediate node rather than directly from the output node, acting as a mediator that isolates the voltage regulation loop from the saturation conditions at the output when external circuits pull down the bus.
2Speed
If bias current is increased to reduce recovery time, then slew rate improves, but power consumption increases and practical limitations are reached
Solution Approach 1:
A current feedback loop is implemented that senses the current at the output node and provides feedback to the output stage. This allows the circuit to respond quickly to current changes and recover rapidly from saturation conditions without requiring excessive bias current, as the feedback mechanism efficiently controls the output stage response.
3Object-affected harmful factors
If clamping methods are applied at the regulated output to reduce transients, then transient voltages are reduced, but available headroom for noise margins is reduced
Solution Approach 1:
The feedback system is segmented into voltage and current loops with different functions. The voltage feedback loop maintains regulation without requiring aggressive clamping, while the current feedback loop handles transient current conditions. This segmentation allows transient reduction without the need for clamping that would reduce noise margins.
Data Source
AI summary
A circuit includes an input stage configured to receive a regulated input signal and generate an input stage output signal in response to the regulated input signal. An isolation stage can be configured to pass the input stage output signal to a buffered output node. The isolation stage receives feedback from the buffered output node to deactivate the buffer input stage if transient voltages are generated at the buffered output node. An output stage can be configured to provide current to the buffered output node in response to the regulated input signal.