PNP Output Circuit Using Variable Base Current for Faster Switching
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Solution Overview
Problem
The existing output circuits using PNP transistors face a long turn-off time due to high base accumulated charge, which hinders high-speed communication by slowing down the switching between ON and OFF states, thereby reducing communication speed with external devices.
Innovation Solution
The output circuit incorporates a PNP first transistor and a first current source that reduces the base current to a predetermined value after the transistor is turned on and before it is turned off, along with additional components like a switch, second current source, and second transistor to rapidly discharge the base accumulated charge and parasitic capacity, thereby shortening the turn-off time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the base current is maintained at a high level during the ON state of the PNP transistor, then the transistor can output sufficient collector current for communication signals, but the base accumulated charge amount increases, causing the turn-off time to become long
Solution Approach 1:
The patent applies dynamics by making the base current variable rather than constant. The base current is dynamically adjusted based on the operational state: a first base current is supplied during turn-on, a second (reduced) base current is supplied during the ON state, and a third (negative) base current is supplied during turn-off. This dynamic adjustment resolves the contradiction by reducing base accumulated charge during the ON state while maintaining sufficient collector current output capability.
Solution Approach 2:
The patent implements periodic action by dividing the transistor operation into distinct phases with different base current characteristics. The base current is periodically adjusted: high during turn-on, reduced during the ON state, and negative during turn-off. This periodic modulation of base current allows the system to optimize both power output and turn-off speed at different time intervals.
2Speed
If the PNP transistor switches between ON and OFF states rapidly for high-speed communication, then communication speed improves, but the base accumulated charge must be quickly discharged, requiring additional circuit elements that increase device complexity
Solution Approach 1:
The patent applies universality by designing the current source to perform multiple functions: it supplies base current during turn-on, reduces base current during the ON state, and discharges base accumulated charge during turn-off. This multi-functional current source eliminates the need for separate dedicated circuits for each function, achieving rapid switching for high-speed communication while minimizing device complexity.
Solution Approach 2:
The patent merges the turn-on, turn-off, and base charge management functions into a single integrated current source circuit. By combining these functions that were traditionally implemented with separate transistors and circuits, the patent achieves rapid switching capability while reducing the overall number of circuit elements and simplifying the device structure.
Data Source
AI summary
An output circuit outputs communication signals and communicates with an external device ED, and includes: a PNP first transistor, which is capable of outputting a collector current as the communication signals; and a first current source, which is capable of changing a base current of the first transistor, and which reduces the base current to a predetermined current value after the first transistor is turned on and before the first transistor is turned off.