P-Channel Output Circuit With Native Pull-Up for Fast Turn-Off
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Solution Overview
Problem
Conventional output circuits using p-channel MOSFETs face issues with pull-up resistor resistance value affecting circuit characteristics and turn-off speed, and require voltage clamp circuits, leading to increased current consumption.
Innovation Solution
An output circuit design incorporating a p-channel output transistor with an enhanced threshold voltage and an n-channel pull-up transistor with a low threshold voltage, utilizing a native-type n-channel MOSFET to quickly pull up the gate voltage when the output transistor is OFF, without the need for a resistor or voltage clamp circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a pull-up resistor is used to pull up the gate of the p-channel MOSFET, then the MOSFET can be turned off, but the resistance value creates a trade-off: small resistance affects gate drive characteristics while large resistance slows down turn-off speed
Solution Approach 1:
The patent changes the type of transistor used for pulling up the gate from a p-channel MOSFET to an n-channel MOSFET. This parameter change allows the pull-up transistor to have a low threshold voltage (native type) while providing strong pull-up capability, resolving the contradiction between turn-off speed and gate drive characteristics
Solution Approach 2:
Instead of using a p-channel transistor (same type as output) for pulling up, the patent uses an n-channel transistor (opposite type). This inversion allows the pull-up transistor to operate with a low threshold voltage and provide effective gate pulling without the trade-offs associated with p-channel transistors
2Speed
If another p-channel transistor is used for pulling up instead of a pull-up resistor, then the transistor can be turned off quickly, but a voltage clamp circuit is required which increases current consumption
Solution Approach 1:
The patent changes the transistor type from p-channel to n-channel for the pull-up function. The n-channel native transistor has a low threshold voltage that allows it to turn on easily for quick gate pulling, while its low operating current eliminates the need for additional clamp circuits and reduces overall current consumption
Solution Approach 2:
The patent extracts the voltage clamp circuit from the design by using an n-channel transistor instead of a p-channel transistor. The n-channel transistor's inherent low threshold voltage characteristics provide the necessary gate pulling without requiring external clamp circuits, thereby eliminating the associated current consumption
Data Source
AI summary
The disclosure includes a p-channel output transistor MP1, of which the drain is connected to the output end; a gate drive circuit A1, which drives the gate voltage of the output transistor; and an n-channel pull-up transistor NAT, which is connected to the gate of the output transistor MP1, and is turned on when the output transistor is OFF to pull up the gate voltage. The output transistor MP1 is of an enhanced type with a relatively high threshold voltage for being turned on, and the pull-up transistor NAT is of a native type with a relatively low threshold voltage for being turned on.