PWM Signal Generation Circuit for Stable Duty Ratio Control
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Solution Overview
Problem
Existing PWM signal generation circuits face challenges in maintaining a constant duty ratio and linear characteristics, particularly when ambient temperature changes, due to the influence of resistors and capacitors, leading to non-linearity in discharge voltage.
Innovation Solution
A PWM signal generation circuit is designed with a charging control circuit, discharging control circuit, comparison circuit, and control logic circuit to manage capacitor charging and discharging, generating a PWM signal with a constant duty ratio and adjusting frequency and duty ratio to mitigate temperature effects and non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a resistor and capacitor are used to generate PWM signal by changing charging/discharging time, then the PWM signal can be generated, but the duty ratio becomes unstable when temperature changes
Solution Approach 1:
The patent changes the fundamental parameters of the PWM generation mechanism by replacing the RC time-constant method with a triangle wave generation method. The triangle wave is generated using integrators and comparators with reference voltages, allowing the PWM duty ratio to be determined by voltage level comparisons rather than temperature-sensitive time constants. This parameter change enables stable duty ratio control across temperature variations.
Solution Approach 2:
The patent substitutes the passive RC charging/discharging mechanism with an active triangle wave generation system using operational amplifiers, integrators, and comparators. This replacement transforms the PWM generation from a time-constant-based passive process to a voltage-comparison-based active process, eliminating temperature sensitivity and improving duty ratio stability.
2Productivity
If a resistor is used to discharge the charged capacitor, then the capacitor can be discharged, but linear characteristics cannot be secured
Solution Approach 1:
The patent replaces the linear resistor-based discharge mechanism with a constant current source implemented using operational amplifiers and transistors. This substitution ensures that the discharge current remains constant regardless of voltage changes, achieving ideal linear discharge characteristics where voltage decreases at a constant rate over time, thus securing both productivity and manufacturing precision.
Solution Approach 2:
The patent changes the discharge mechanism from resistance-based (non-linear) to constant current-based (linear). By using an operational amplifier to regulate the discharge current and maintain it constant, the discharge voltage becomes linearly proportional to time, achieving the desired linearity while maintaining efficient discharge speed.
3Adaptability or versatility
If resistor and capacitor values are changed to adjust PWM characteristics, then the PWM signal parameters can be modified, but the duty ratio is affected by temperature changes
Solution Approach 1:
The patent fundamentally changes the PWM generation approach from RC time-constant-based to triangle wave voltage-comparison-based. This allows PWM parameters to be adjusted by changing voltage levels and integration time constants rather than resistor/capacitor values, making the system adaptable while immune to temperature effects that plague passive component-based designs.
Solution Approach 2:
The patent employs feedback mechanisms through operational amplifiers and comparators that continuously monitor voltage levels and adjust the triangle wave generation and PWM output accordingly. This closed-loop approach compensates for any drift and maintains accurate duty ratio control regardless of temperature variations, while still allowing parameter adjustment through reference voltage settings.
Data Source
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AI summary
Disclosed is a pulse width modulation signal generation circuit (200_1) including a charging control circuit (212) connected to and located between a first node (ND1) connected to a capacitor (C1) and a voltage line (PWL) that supplies an operating voltage (VDD), wherein the charging control circuit controls a charging operation for the capacitor in response to an activated charging control signal (CNT1), a discharging control circuit (214) connected to and located between the first node (ND1) and ground, wherein the discharging control circuit controls a discharging operation for the capacitor in response to an activated discharging control signal (CNT2), a comparison circuit (220, 230) that generates a comparison signal (CMP1, CMP2) by comparing a first reference voltage (Vref1) and a second reference voltage (Vref2) with a voltage of the first node (VND1), and a control logic circuit (240) that generates a pulse width modulation signal (SPWM) whose level changes based on a level change of the comparison signal (CMP1, CMP2) and determines a level change timing for the activation of the charging control signal (CNT1) and the discharging control signal (CNT2) using the level change of the comparison signal (CMP1, CMP2).