Alternating Capacitor Ramp Generator for Linear PWM Signals
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Solution Overview
Problem
High-speed ramp generators in PWM circuits suffer from limited slew time, leading to nonlinearity and harmonic distortion in voltage ramp signals due to fast discharge, which limits the speed and quality of switching regulators.
Innovation Solution
An improved ramp generator design using two preliminary voltage ramp signals generated by alternatingly charging separate capacitors, allowing for slow reset times and multiplexing between them to produce an output voltage ramp signal with high linearity, reducing noise and nonlinearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fast discharge is used to reset the capacitor, then the ramp generator speed is improved, but linearity deteriorates due to ringing, overshoot, and undershoot
Solution Approach 1:
The patent divides the single capacitor into two separate capacitors (first and second capacitors), each generating preliminary ramp signals independently. This segmentation allows each capacitor to be discharged slowly without affecting the other, eliminating ringing and overshoot while maintaining high-speed operation through alternating selection of the two capacitors.
Solution Approach 2:
The patent employs periodic action by alternating between two preliminary ramp signals generated by separate capacitors. While one capacitor is being used to generate a continuous ramp signal, the other capacitor is discharged slowly in the background. This periodic switching between two capacitors allows fast effective reset without the harmful effects of fast discharge on a single capacitor.
2Manufacturing precision
If slow discharge is used to reset the capacitor, then linearity is improved, but the ramp generator speed deteriorates
Solution Approach 1:
The patent merges two separate ramp generation paths into a single output by using switches to alternately connect the output node to either the first or second capacitor. This combining approach allows the system to benefit from the linearity of slow discharge while maintaining high speed through the coordinated operation of two capacitors working in parallel.
Solution Approach 2:
The patent employs periodic action by alternating between two preliminary ramp signals generated by separate capacitors. While one capacitor is being used to generate a continuous ramp signal, the other capacitor is discharged slowly in the background. This periodic switching between two capacitors allows fast effective reset without the harmful effects of fast discharge on a single capacitor.
3Device complexity
If a single capacitor is used, then device complexity is reduced, but the ability to achieve both high speed and high linearity deteriorates
Solution Approach 1:
The patent divides the single capacitor into two separate capacitors (first and second capacitors), each generating preliminary ramp signals independently. This segmentation allows each capacitor to be discharged slowly without affecting the other, eliminating ringing and overshoot while maintaining high-speed operation through alternating selection of the two capacitors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves a high degree of linearity in the output voltage ramp signal, reducing noise and harmonic distortion, and enabling faster and more precise switching in high-speed applications.
Implementation Method 1
A common design for generating a voltage ramp signal uses a capacitor repeatedly charged by a current source
Data Source
AI summary
An improved ramp generator enables a very high degree of linearity in an output voltage ramp signal. Output ramps of the output voltage ramp signal are alternatingly produced from two preliminary ramp signals during alternating time periods. Preliminary ramps are produced at different preliminary ramp nodes that are alternatingly connected to an output node. The preliminary ramps continuously ramp during and in some cases beyond, e.g., before and/or after, the time periods. In some embodiments, switches alternatingly connect two capacitors to at least one current source, a reset voltage source, and the output node to alternatingly produce the preliminary ramps.