Slew-Limited Output Driver Circuit With Switchable Current Mirror
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Solution Overview
Problem
Existing output driver circuits face challenges with electromagnetic emissions and noise due to fast rise times, and high output currents lead to reduced lifespan, while current limiting methods require significant layout space and complex circuitry, and voltage profile adjustments are non-linear and prone to electrostatic discharge.
Innovation Solution
A slew-limited output driver circuit utilizing a switchable current mirror controlled by control signals and output current level, allowing for adjustable operating modes without additional components, providing integrated protection against electrostatic discharge and short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the output current is limited using resistors in the output path, then the electromagnetic emissions and noise are reduced, but the layout space requirement increases and the signal level is disturbed
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary element to limit the output current. Instead of using resistors directly in the output path, the current mirror (comprising transistors P1, P2, N1, N2 and control circuitry) acts as a mediator that regulates current flow through feedback mechanisms, thereby reducing electromagnetic emissions without requiring large layout space or disturbing the signal level at the output.
Solution Approach 2:
The patent employs feedback control to regulate the output current. The current mirror circuit monitors the output current level and adjusts the driving signal accordingly through feedback paths (involving transistors and control nodes), enabling dynamic current limitation that reduces electromagnetic emissions while maintaining signal integrity and minimizing layout space requirements.
2Speed
If a current source is used as an output driver, then the rise time is limited, but no low-impedance driver is feasible and the signal level at the resistive load is disturbed
Solution Approach 1:
The patent implements a dynamic output driver that can switch between different operating modes. The circuit uses controllable transistors (P1, P2, N1, N2) and control signals to dynamically adjust the output impedance and current driving capability. This allows the circuit to provide slew-rate limiting for controlled rise times while maintaining low output impedance when needed, thereby avoiding signal level disturbance at resistive loads.
Solution Approach 2:
The patent creates a multi-functional output driver that can operate in different modes depending on the application requirements. The same circuit structure can provide both slew-rate limiting (for controlled rise times) and low-impedance driving (for signal integrity), making it universally applicable to different load conditions without requiring separate circuits for each function.
3Duration of action of stationary object
If the output current is reduced to extend circuit life, then the lifespan is improved, but the driving capability is reduced
Solution Approach 1:
The patent uses periodic or pulsed current limiting through the current mirror circuit. Instead of continuously reducing the output current, the circuit applies current limitation only during switching transitions when slew-rate control is needed. During steady-state operation, the circuit can provide full driving capability, thus extending circuit lifespan through controlled stress reduction while maintaining adequate driving power when required.
Data Source
AI summary
A slew-limited output driver circuit facilitates finding a circuitry that allows a flexible setting of the slew-rate of an integrated circuit, with only a small footprint and latency, and which allows realizing different driver modes without additional components integrated protection against ESD. A short circuit will be solved by a slew-limited output driver circuit comprising a switchable current mirror providing an output current equal to an input current, wherein the current mirror is controlled by an additional switch, which is switched in response to control signals and/or an output current level of the output driver circuit, wherein adjustable operating modes of the slew-limited output driver circuit are realized by the control signals.