Slew-Rate Controlled Driver Using Output Current Sensing
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Solution Overview
Problem
Existing driver technologies face challenges in controlling slew rate independently of load capacitance, requiring large feedback capacitors that increase chip area and power consumption.
Innovation Solution
A driver design that senses output current to indirectly detect load capacitance and dynamically adjusts pre-drive current, enabling additional current when a large load is detected, thereby controlling slew rate without the need for large feedback capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If large feedback capacitors are used to control slew rate independently of load capacitance, then slew rate control is improved, but chip area increases
Solution Approach 1:
The patent extracts the load capacitance detection function from the traditional feedback capacitor-based slew rate control mechanism. By using a current sensor to detect output current (which reflects load capacitance) and separately controlling the pre-drive current based on this detection, the system eliminates the need for large feedback capacitors while maintaining slew rate control capability.
Solution Approach 2:
The patent segments the slew rate control function into two independent parts: (1) load capacitance detection through output current sensing, and (2) pre-drive current adjustment based on detected load. This segmentation allows each function to be optimized separately, avoiding the need for large capacitors that would be required in a unified feedback approach.
2Manufacturing precision
If large feedback capacitors are used to control slew rate independently of load capacitance, then slew rate control is improved, but power consumption increases
Solution Approach 1:
The patent extracts the energy-consuming feedback capacitor from the slew rate control mechanism and replaces it with a low-power current sensing approach. The current sensor and control circuit consume significantly less power than large feedback capacitors would require to achieve the same slew rate control performance.
Solution Approach 2:
By segmenting the control mechanism into separate current sensing and pre-drive adjustment stages, the patent enables precise control with minimal power consumption at each stage, avoiding the continuous energy storage and discharge cycles that large feedback capacitors would require.
3Area of stationary object
If output current is sensed to detect load capacitance and dynamically adjust pre-drive current, then chip area is reduced, but device complexity increases
Solution Approach 1:
The patent introduces a current sensor as an intermediary element that bridges the output stage and the pre-drive control circuit. This intermediary converts the load capacitance information into an easily measurable output current signal, which then triggers appropriate pre-drive current adjustment. This approach simplifies the overall control logic compared to direct capacitance measurement while maintaining area efficiency.
Data Source
AI summary
According to certain aspects, a driver includes an output transistor coupled between a first rail and an output of the driver, a first current source coupled to a gate of the output transistor, a second current source, and a switch, wherein the switch and the second current source are coupled in series between the gate of the output transistor and a second rail. The driver also includes a current sensor configured to generate a sense current based on an output current of the driver, and a reference current source configured to generate a reference current, wherein the current sensor and the reference current source are coupled to a control input of the switch.