PWM Power Detection Circuit for Linear Low-Noise Sensing
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Solution Overview
Problem
Conventional power detection systems face challenges such as complex circuit designs, limited linearity range, high noise, and poor temperature stability, particularly in applications like flyback power converters.
Innovation Solution
The proposed system employs a combination of signal converters and a low-pass filter to generate a power detection signal. This system includes a first signal converter that generates a pulse-width-modulation signal from an input signal, a second signal converter that generates a voltage signal from another input signal, and a low-pass filter that combines these signals to produce a power detection signal that represents the input power, with a linear change in magnitude with respect to the input power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog multiplier is used to multiply voltage and current signals for power detection, then power detection can be achieved, but the circuit design becomes complex
Solution Approach 1:
The patent extracts the multiplication function from a complex analog multiplier circuit and implements it through simpler components: a pulse-width modulator that converts one signal to PWM duty cycle, and a low-pass filter that extracts the average value. This separation of functions eliminates the need for complex analog multiplication while achieving the same power detection result.
Solution Approach 2:
The patent replaces the analog multiplier (electronic system) with a pulse-width modulation system combined with low-pass filtering. Instead of directly multiplying analog signals, the system uses PWM encoding followed by average value extraction, which is implemented with simpler electronic components and achieves equivalent functionality.
2Measurement precision
If an analog multiplier is used for power detection, then power calculation is possible, but the linearity range becomes small
Solution Approach 1:
The patent introduces dynamic PWM modulation where the duty cycle dynamically follows the instantaneous value of one input signal. This dynamic encoding approach, combined with the low-pass filter's averaging effect, creates a linear relationship between the output and the product of input signals across a wider range, overcoming the limited linearity of traditional analog multipliers.
3Measurement precision
If an analog multiplier is used for power detection, then power signal can be generated, but noise increases
Solution Approach 1:
The patent uses periodic PWM signals with a fixed frequency to encode the input signals. The low-pass filter is designed with a cutoff frequency that passes the PWM frequency components while attenuating higher frequency noise. This periodic modulation approach naturally separates the signal from noise, improving the signal-to-noise ratio in power detection.
Solution Approach 2:
The low-pass filter acts as an intermediary between the PWM modulator and the power detection output. It mediates by filtering out high-frequency noise components from the PWM signal while preserving the useful information contained in the duty cycle variations, thus reducing noise in the final power detection result.
4Measurement precision
If an analog multiplier is used for power detection, then power calculation is achieved, but temperature stability deteriorates
Solution Approach 1:
The patent replaces temperature-sensitive analog multiplier components with digital-like PWM generation and simple low-pass filtering. The PWM modulator uses voltage or current comparison against a reference, and the low-pass filter uses passive RC components, both of which are less sensitive to temperature variations than the transistors and resistors in an analog multiplier, thereby improving temperature stability.
Data Source
AI summary
System and method for detecting a power. For example, a system for detecting a power includes: a first signal converter configured to receive a first signal and generate a pulse-width-modulation signal based at least in part on the first signal; a second signal converter configured to receive a second signal and generate a voltage signal based at least in part on the second signal; and a low-pass filter configured to receive the pulse-width-modulation signal and the voltage signal and generate a power detection signal based at least in part on the pulse-width-modulation signal and the voltage signal; wherein: the first signal is either an input current or an input voltage; the second signal is either the input current or the input voltage; and the first signal and the second signal are different.