Frequency-Tracking Ramp Generator for Wide-Range PWM Control
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Solution Overview
Problem
Existing ramp generators are limited to fixed frequency or narrow frequency range applications due to the proportional relationship between the peak voltage of the ramp signal and the switching period, making them unsuitable for wide frequency range operations.
Innovation Solution
The implementation of a ramp generator with a variable resistor that tracks the frequency of the PWM clock signal, and a switched capacitor configuration that maintains the amplitude of the ramp signal independent of frequency, allowing for a wide range of frequency operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed frequency ramp generator is used, then the ramp signal stability is maintained, but the device cannot operate over a wide frequency range
Solution Approach 1:
The patent applies dynamics by making the resistor value variable rather than fixed. The resistor is controlled by a frequency-dependent signal that tracks the PWM clock frequency, allowing the ramp generator to adapt its parameters dynamically to maintain stability across different operating frequencies.
Solution Approach 2:
The patent changes the resistor parameter from a fixed value to a variable value that depends on the operating frequency. This is achieved by connecting the resistor to a frequency-tracking control signal, which adjusts the effective resistance to maintain proper ramp signal characteristics across a wide frequency range.
2Adaptability or versatility
If the peak voltage of the ramp signal is proportional to the switching period, then the circuit is simple, but the device is limited to fixed or narrow frequency range applications
Solution Approach 1:
The patent introduces an intermediary frequency-tracking signal that mediates between the PWM clock and the resistor. This intermediary control signal allows the resistor to be adjusted in proportion to the frequency without requiring a completely complex reconfiguration of the ramp generator circuitry.
Solution Approach 2:
The patent makes the resistor serve multiple functions: it provides the necessary resistance for ramp generation while also being dynamically controllable to track frequency changes. This multi-functionality allows a single component to address both the simplicity requirement and the wide frequency range requirement.
3Adaptability or versatility
If additional trimming is implemented to achieve stable operation, then the frequency range can be extended, but the manufacturing cost increases
Solution Approach 1:
The patent implements self-service by having the circuit automatically adjust its own parameters through the frequency-tracking control signal. The resistor is self-regulated by the operating frequency without requiring external trimming or manual adjustment, enabling wide frequency range operation while maintaining ease of manufacture.
Data Source
AI summary
A ramp generator includes a current generator, a current mirror, and a first capacitor. The current generator has an input for receiving a clock signal, and an output for providing a current proportional to a frequency of the clock signal using a first transistor having first and second current electrodes and a control electrode, an amplifier that establishes a reference voltage on the second current electrode of the first transistor, and a variable resistor coupled between the second current electrode of the second transistor and ground whose resistance is set according to the frequency of the clock signal. The current mirror has an input coupled to the first terminal of the first transistor, and a second terminal. The first capacitor has a first terminal coupled to the output of the current mirror and providing a ramp signal, and a second terminal coupled to the first power supply voltage terminal.