Op-Amp Slew Rate Circuit With Edge-Triggered Current Compensation

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Solution Overview

Problem

Conventional slew rate enhancement circuits in display panel systems face challenges in controlling the slew rate due to vulnerability to PVT variations, leading to unpredictable current enhancement, abnormal output waveforms, excessive power consumption, and electromagnetic interference, especially as display panel resolution increases and charging time shortens.

Innovation Solution

A slew rate enhancement circuit comprising a signal edge detector, comparator, and adjustment unit that generates a control signal based on the difference between input and output signals to independently enhance the rising and falling edges of the output waveform, using current sources to linearly control the slew rate and adjust for different power modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional transconductance capability of MOSFETs is used to generate enhanced current, then slew rate enhancement is achieved, but the enhanced current becomes unpredictable and uncontrolled due to PVT variations

Engineering Contradiction:

Improveslew rateVSAvoidcurrent control stability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the control parameter from exponential transconductance (gm) to linear current sources controlled by voltage signals. The current sources are controlled by voltage signals derived from the difference between input and output signals, providing linear and predictable current enhancement that is insensitive to PVT variations.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the MOSFET transconductance mechanism with a voltage-controlled current source mechanism. This substitution eliminates the exponential relationship between gate voltage and drain current, replacing it with a linear controlled current that can be precisely regulated through voltage signals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Speed

If uncontrolled enhanced current is generated, then slew rate is enhanced, but the buffer circuit enters linear region and produces abnormal output waveforms

Engineering Contradiction:

Improveslew rateVSAvoidoutput waveform accuracy

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent implements feedback by deriving the control signal for the current source from the difference between the input signal and output signal. This feedback mechanism ensures that the enhanced current is applied only when needed (during transitions) and automatically reduces when the output approaches the input, preventing the buffer from entering the linear region and maintaining waveform accuracy.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent makes the current enhancement dynamic by controlling the current source with a voltage signal that varies with the signal transition. The current source is activated during rising and falling edges and deactivated during steady states, providing dynamic adaptation to signal conditions while maintaining waveform integrity.

Inventive Principle:

Principle #15Dynamics

3Speed

If excessive current enhancement is applied, then slew rate is improved, but power consumption and electromagnetic interference increase

Engineering Contradiction:

Improveslew rateVSAvoidpower consumption

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The patent applies periodic action by enabling the current sources only during signal transitions (rising and falling edges) rather than continuously. The control circuit activates the current sources temporarily during edge detection and disables them during steady states, reducing overall power consumption while maintaining high slew rate during critical transitions.

Inventive Principle:

Principle #19Periodic action

4Ease of operation

If different devices are used for detecting rising edge and falling edge, then edge detection is achieved, but the output waveform becomes asymmetric

Engineering Contradiction:

Improveedge detection capabilityVSAvoidwaveform symmetry

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The patent applies homogeneity by using the same type of devices (e.g., both PMOS or both NMOS transistors) for detecting both rising and falling edges. This symmetric device configuration ensures that both edges are detected with identical characteristics, producing symmetric output waveforms and eliminating the asymmetry problem caused by using different device types.

Inventive Principle:

Principle #33Homogeneity

Data Source

PatentUS11081036B1Slew rate enhancement circuit

Publication Date: 2021.08.03 NOVATEK MICROELECTRONICS CORP

AI summary

The disclosure provides a slew rate enhancement apparatus that is connected to an operational amplifier that receives an input signal and generates an output signal according to the input signal for driving a pixel. The slew rate enhancement apparatus comprises a signal edge detector, a comparator, an adjustment unit. The signal edge detector is coupled to the operational amplifier and configured to detect a signal edge and outputting a difference signal corresponding to a difference between the input and output signals. The comparator is coupled to the signal edge detector to receive the difference signal and configured to generate a control signal according to the difference signal. The adjustment unit is coupled to the comparator to receive the control signal, and configured to couple a compensation signal generated by a current source to the operational amplifier according to the control signal to enhance a slew rate of the operation amplifier.