Switchable Current Source Circuit Fast Turn-On
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Solution Overview
Problem
Current switchable current source circuits face challenges in achieving fast turn-on speed without introducing instability, particularly when the ratio between input and output transistors is large, and require high power for high-speed operation.
Innovation Solution
A switching circuit that precharges a charge storage device to a voltage higher than the desired gate voltage of the output transistor and then discharges it, using an isolating switch to control the gate voltage, thereby providing controlled charge flow rather than controlled voltage, and includes a discharge switch to manage the gate voltage of the output transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a current mirror circuit with large transistor size ratio is used to achieve fast turn-on speed, then the switching speed is improved, but the circuit becomes unstable
Solution Approach 1:
The patent divides the current mirror circuit into separate stages: an input stage with a first current mirror and an output stage with a second current mirror. The isolating switch disconnects these stages during switching operations, preventing instability from propagating while allowing fast switching in the output stage.
Solution Approach 2:
The isolating switch acts as an intermediary between the input and output stages. It blocks the feedback path during switching, preventing the large transistor ratio in the output stage from causing instability in the overall circuit while still enabling fast turn-on.
2Speed
If high current is used to charge the gate for fast switching, then the switching speed is improved, but the power consumption increases
Solution Approach 1:
The patent precharges a storage capacitor during the steady-state period before switching. This stored charge is then rapidly discharged through the output transistor gate during switching, enabling fast turn-on without requiring high instantaneous current from the reference current source.
Solution Approach 2:
The circuit uses its own reference current to precharge the storage capacitor during normal operation. This self-service mechanism prepares the necessary charge in advance, so that switching can occur rapidly without drawing excessive power during the switching event itself.
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 enhances turn-on speed without stability issues and reduces power consumption, allowing for precise control of the output current with minimal current flow between stages, achieving rapid and stable switching.
Implementation Method 1
a charge storage device for storing the reference voltage
Implementation Method 2
an isolating switch for selectively coupling or isolating the gate of the output transistor to or from the charge storage device
Implementation Method 3
a discharge switch for discharging the gate of the output transistor
Data Source
Figure 1~2
Figure 3(a)~3(c)
Figure 4(a)~5
AI summary
A method and circuit for providing a switched current source output has a precharge mode, in which a charge storage device is charged to a reference voltage, and the gate of an output transistor is discharged. In a discharge mode, the charge storage device is discharged to the gate of the output transistor to raise the gate voltage by an amount depending on the charge flow.