Current Sense Cascode Amplifier for High-Speed Buck Regulator Protection
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Solution Overview
Problem
Existing DC-DC switching converters face challenges in achieving high-speed and high-accuracy current sensing for short-circuit protection and performance optimization, particularly in buck regulators, while also requiring a small area to maintain low cost and flexibility for varying input voltages.
Innovation Solution
The implementation of a current sense circuit using a cascode amplifier configuration with a cascode current mirror and a non-inverting common gate amplifier, which includes a high side power switch for current sensing and utilizes bias currents for both the amplifier and sense devices, allowing for high voltage input compatibility and low loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sense circuit is implemented with high-speed and high-accuracy requirements, then measurement precision and reliability are improved, but device complexity and area increase
Solution Approach 1:
The current sense circuit is divided into two functional stages: a first stage with a common-source amplifier and cascode current mirror for high-accuracy current sensing, and a second stage with a common-gate amplifier for signal buffering and driving. This segmentation allows each stage to be optimized for its specific function, achieving high measurement precision while managing overall circuit complexity through modular design.
2Productivity
If a current sense circuit is implemented with high-speed requirements, then productivity and response time are improved, but device complexity and power consumption increase
Solution Approach 1:
The cascode current mirror employs dynamic biasing techniques where bias currents are optimized to achieve high switching speeds during transient conditions. The common-gate amplifier in the second stage provides low output impedance that enhances the circuit's ability to drive capacitive loads quickly, thereby improving productivity and response time while maintaining manageable complexity through dynamic operation rather than static high-complexity design.
3Area of stationary object
If a compact current sense circuit is implemented to reduce area, then ease of manufacture and cost are improved, but measurement precision and reliability may deteriorate
Solution Approach 1:
The circuit merges the current sensing function and the signal amplification function into a single integrated structure. The cascode current mirror simultaneously performs current replication and signal amplification, while the common-gate amplifier provides both impedance transformation and additional gain. This merging eliminates the need for separate discrete components, reducing the overall circuit area while maintaining measurement precision through the coordinated operation of the combined functions.
4Adaptability or versatility
If high voltage input compatibility is required, then adaptability is improved, but device complexity and loss increase
Solution Approach 1:
The cascode current mirror is configured with its cascode transistor gates connected to an optimized bias voltage that is established in advance. This preliminary biasing action ensures that the mirror can accurately sense and replicate currents across a wide range of input voltages without requiring complex voltage regulation circuits. The bias voltage is pre-configured to accommodate high voltage inputs, achieving adaptability while minimizing power loss through efficient bias current management.
Data Source
AI summary
A current sense amplifier sensing current through a main switch of a converter. The amplifier includes first and second switch devices, an amplifier control circuit, a bias circuit, a current generator circuit, and a sense circuit. The main switch is coupled to an input, phase and control nodes. The first and second switch devices are smaller matching versions of the main switch and are both coupled to the main switch and form first and second nodes. The bias circuit is coupled between second and fourth nodes and the amplifier control circuit is coupled between first and third nodes. The current generator develops a first current through the amplifier control circuit and a second current through the bias circuit. The sense circuit has a current path coupled to the first node and is controlled by the third node to develop a sense voltage indicative of current through the main switch.