Current-Sensed Slew-Rate Driver Without Large Feedback Capacitors

Solution Overview

Problem

Existing slew-rate controlled drivers require large feedback capacitors for effective slew-rate control, which increases chip area and power consumption, and are not efficient in managing variations in load capacitance across different transmission lines.

Innovation Solution

The proposed solution involves a driver design that senses the output current to indirectly detect load capacitance and dynamically adjusts pre-drive current using additional current sources, eliminating the need for large feedback capacitors by enabling or disabling these sources based on sensed current thresholds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If large feedback capacitors are used for slew-rate control, then slew-rate control effectiveness is improved, but chip area and power consumption increase

Engineering Contradiction:

Improveslew-rate control effectivenessVSAvoidchip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent changes the control parameter from capacitor-based feedback to current-based feedback. By sensing the output current and comparing it to a threshold, the system dynamically adjusts the pre-drive current without requiring large feedback capacitors. This parameter change from voltage/capacitance to current enables effective slew-rate control with reduced chip area.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional capacitive feedback mechanism with a current sensing and control mechanism. Instead of using large feedback capacitors to control the slew rate, the system uses current sensors to detect output current and control circuits to adjust pre-drive current, substituting the mechanical/capacitive approach with an electronic current-based approach that consumes less area and power.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If large feedback capacitors are used for slew-rate control, then slew-rate control effectiveness is improved, but power consumption increases

Engineering Contradiction:

Improveslew-rate control effectivenessVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The patent changes the control parameter from capacitor-based feedback to current-based feedback. By sensing the output current and comparing it to a threshold, the system dynamically adjusts the pre-drive current without requiring large feedback capacitors. This parameter change from voltage/capacitance to current enables effective slew-rate control with reduced chip area.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional capacitive feedback mechanism with a current sensing and control mechanism. Instead of using large feedback capacitors to control the slew rate, the system uses current sensors to detect output current and control circuits to adjust pre-drive current, substituting the mechanical/capacitive approach with an electronic current-based approach that consumes less area and power.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If fixed pre-drive current is used, then device complexity is reduced, but adaptability to varying load capacitance deteriorates

Engineering Contradiction:

Improvedevice complexityVSAvoidadaptability to load capacitance variation

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamic adjustment of the pre-drive current based on the sensed output current. The control circuit enables or disables the second current source dynamically according to whether the output current exceeds a threshold. This dynamic adaptation allows the driver to automatically adjust to varying load capacitances without requiring complex design specifications for different transmission line scenarios.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent introduces a feedback mechanism where the output current is sensed and fed back to the control circuit. This feedback enables the system to automatically adjust the pre-drive current based on the actual load conditions. The feedback loop compares the sensed current with a threshold and adjusts the current sources accordingly, providing adaptability to varying load capacitance without increasing overall device complexity.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS11190173B2Area efficient slew-rate controlled driver

Publication Date: 2021.11.30 QUALCOMM INC

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.