Optical Voltage Measurement for High-Side FETs
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Solution Overview
Problem
Conventional voltage measurement systems fail to accurately measure gate-to-source voltage in high-side FETs due to common-mode source voltage changes with fast slew rates, requiring low capacitance and electrical isolation, which is challenging especially in high-voltage floating environments like electric vehicle power train electronics.
Innovation Solution
The system employs a pulse-width modulator to convert input voltage waveforms into PWM signals, which are then optically transmitted and received, using a transimpedance amplifier and filters to recover the original voltage waveform, and a voltage-controlled oscillator to convert analog voltage to frequency-modulated signals for accurate measurement, ensuring galvanic isolation and high bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amplitude modulated laser is used for voltage measurement, then electrical isolation and bandwidth requirements are met, but accurate DC measurements become challenging due to charge storage effects and measurement drifts
Solution Approach 1:
The patent replaces the mechanical/electrical coupling system (amplitude modulated laser with direct electrical connection) with an optical communication system. The voltage signal is converted to optical domain through modulation, transmitted via optical fiber, and converted back to electrical signal at the receiver, achieving galvanic isolation while maintaining measurement accuracy including DC components
Solution Approach 2:
The patent changes the modulation parameter from amplitude modulation to frequency modulation. By modulating the laser frequency rather than amplitude, the system eliminates charge storage effects in the modulator that cause DC drift, while preserving the ability to measure DC voltage components accurately through frequency demodulation
2Measurement precision
If additional circuits with slow ADC and communication path are added to capture DC portion, then DC measurement accuracy is improved, but system complexity and cost increase
Solution Approach 1:
The patent makes the frequency modulated optical system universally capable of measuring both AC and DC voltage components through a single measurement path. The frequency demodulation process naturally recovers both dynamic and static voltage components, eliminating the need for separate DC measurement circuits and reducing overall system complexity
3Measurement precision
If measurement system requires low capacitance for high common mode rejection, then measurement precision is improved, but physical size of the system must be small
Solution Approach 1:
The patent replaces the electrical measurement system with high capacitance requirements with an optical measurement system. The optical probe can be made physically small since it doesn't require large capacitive elements for common mode rejection, as the rejection is achieved through optical isolation and frequency demodulation rather than electrical capacitance matching
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
This approach enables accurate differential voltage measurements across high-side FETs with high common-mode rejection, overcoming the limitations of amplitude modulated lasers by providing precise DC measurements without measurement drift, reducing complexity and cost.
Implementation Method 1
a pulse-width modulator configured to receive an input voltage waveform from a device under test (DUT), and to output a PWM signal mapped to the input voltage waveform
Implementation Method 2
an optical transmitter configured to be modulated by the PWM signal to output an optical pulse signal having pulse widths corresponding to pulse widths of the PWM signal
Implementation Method 3
an optical receiver configured to receive the optical pulse signal over an optical link and to convert the optical pulse signal to an electrical current
Implementation Method 4
a voltage-controlled oscillator (VCO) configured to receive an analog input voltage waveform from a DUT, and to output a VCO signal having a frequency mapped to the analog input voltage waveform
Data Source
AI summary
A system for measuring voltage includes a pulse-width modulator or voltage controlled oscillator (VCO) configured to receive an input voltage waveform from a DUT, and to output a pulse-width modulated (PWM) signal or frequency modulated (FM) signal mapped to the input voltage waveform, respectively; an optical transmitter configured to be modulated by the PWM signal or the FM signal to output an optical pulse signal having pulse widths corresponding to pulse widths of the PWM signal or equal to the frequency of the FM signal, respectively; an optical receiver configured to receive the optical pulse signal over an optical link and to convert the optical pulse signal to an electrical current; a transimpedance amplifier (TIA) configured to convert the electrical current to a voltage signal; and at least one filter or detection circuit configured to recover the input voltage waveform or provide numeric values corresponding to the input voltage waveform.