Buffer Circuit Voltage Shifting for Wide LDO Output Range
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Solution Overview
Problem
Buffer circuits in electronic circuits, particularly in low dropout (LDO) regulators, often have constrained output voltage ranges, which limits their ability to drive subsequent circuit stages effectively, especially when large currents are required, necessitating a solution to extend the output voltage range.
Innovation Solution
Incorporating a voltage shift circuit within the buffer circuit that adjusts its output voltage based on the current from the pass transistor, utilizing a combination of transistors to increase the voltage drop across the shift circuit as output current increases, thereby enhancing the drive capability and extending the output voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional buffer circuit is used in an LDO regulator, then the circuit structure is simple, but the output voltage range is constrained and the drive capability is limited
Solution Approach 1:
The buffer circuit is divided into two functional segments: a conventional buffer stage and an added voltage shift circuit. This segmentation allows each part to perform its specialized function - the buffer provides voltage following while the shift circuit extends the output range, resolving the contradiction between simplicity and adaptability
Solution Approach 2:
A voltage shift circuit is introduced as an intermediary component between the buffer output and the pass transistor input. This intermediary circuit translates the buffer's limited output range into an extended effective range, enabling the buffer to drive the pass transistor across a wider voltage range without increasing the buffer's inherent complexity
2Power
If the buffer circuit drives large currents to the pass transistor, then the drive capability is improved, but the output voltage cannot be driven close to ground
Solution Approach 1:
The voltage shift circuit dynamically changes its voltage shift parameter based on the buffer output voltage. When the buffer outputs higher voltages, the shift circuit applies a larger negative shift to bring the final output close to ground while maintaining high drive capability. This dynamic parameter adjustment resolves the contradiction between drive capability and output voltage range
3Power
If a larger pass transistor is used to support higher currents, then the drive capability is improved, but the silicon area increases
Solution Approach 1:
The voltage shift circuit acts as an intermediary that enables a smaller pass transistor to achieve the same effective drive capability as a larger transistor would provide alone. By pre-shifting the voltage to account for the transistor's voltage drop at high currents, the circuit achieves high current handling with reduced silicon area
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the drive capability of the buffer circuit, allowing it to achieve lower output voltages and support higher currents, reducing the size of the pass transistor and overall silicon area while maintaining a wide output voltage range, thus enhancing the performance and efficiency of LDO regulators.
Implementation Method 1
A voltage drop across the voltage shift circuit changes based on a current from the voltage shift circuit
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
In one embodiment, a circuit includes a first transistor having a control terminal, a first terminal, and a second terminal where the first transistor is a first device type. The control terminal of the first transistor receives an input signal. The circuit also includes a second transistor having a control terminal, a first terminal, and a second terminal where the second transistor is a second device type. The control terminal of the second transistor is coupled to the second terminal of the first transistor. A voltage shift circuit has an input coupled to the first terminal of the first transistor and an output coupled to the first terminal of the second transistor and a voltage between the input of the voltage shift circuit and an output of the voltage shift circuit increases as a current from the output of the voltage shift circuit increases.