Cascode Voltage Regulator With Current Mirror Overcurrent Cutoff
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Solution Overview
Problem
Existing voltage regulator circuits face limitations in high voltage applications due to the maximum allowable input voltage limit set by the maximum drain to source voltage of transistors, restricting circuit configurations and design possibilities.
Innovation Solution
A cascode voltage regulator circuit utilizing drain-extended transistors, which allows for higher input voltages by configuring a cascode source follower with current limiting capabilities and a current mirror to manage high current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional transistors are used in voltage regulator circuits, then the circuit design is simple, but the maximum allowable input voltage is limited by the transistor's drain to source voltage rating
Solution Approach 1:
The patent divides the voltage handling function into multiple transistors arranged in a cascode configuration. Each transistor handles a portion of the total voltage, allowing the circuit to accommodate input voltages higher than any single transistor's rating while maintaining manageable individual device stresses.
Solution Approach 2:
The cascode structure nests transistors in series where the source of one transistor is connected to the drain of another. This nested arrangement allows voltage stacking, where each transistor's voltage rating is utilized efficiently to achieve a higher overall voltage capability without proportionally increasing device count.
2Adaptability or versatility
If the number of transistors is increased to handle higher voltages, then the input voltage capability is improved, but the circuit complexity and cost increase
Solution Approach 1:
The cascode transistor configuration serves multiple functions simultaneously: voltage division, current regulation, and output buffering. This multi-functionality reduces the need for separate dedicated components for each function, thereby simplifying the overall circuit and reducing component count despite the higher voltage handling requirement.
3Reliability
If current limiting is added to protect against high current conditions, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The current limiting function is merged into the cascode transistor structure itself. The series connection of transistors in the cascode configuration naturally limits current flow, and the same transistors that provide voltage handling also provide current protection, eliminating the need for separate current limiting components.
Data Source
AI summary
An example cascode voltage regulator circuit includes a first transistor coupled to an input voltage terminal and configured as a source follower to provide an output voltage at a source terminal, a second transistor coupled in series between the source terminal of the first transistor and an output terminal, the second transistor configured as a current limiter, and a current mirror coupled between respective first and second control terminals of the first and second transistors, the current mirror configured to receive a first current indicative of a source follower current flowing through the first transistor and to turn off the second transistor by coupling the first and second control terminals together responsive to the source follower current exceeding a threshold. In an example, the first transistor is a drain-extended NMOS device and the second transistor is a drain-extended PMOS device.