Light-to-Frequency Modulator Calibration for Residual Voltage Accuracy
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Solution Overview
Problem
Existing light-to-frequency modulator circuits face limitations in accuracy due to insufficient time to generate pulses at the end of integration time, leading to incomplete measurement of light intensity, particularly at low signal counts.
Innovation Solution
The system includes a photodiode, integrator, comparator, reference charge circuit, and digital controller to measure residual voltage by disconnecting the photodiode from the integrator and applying a reference voltage via a resistance, allowing for calibration and accurate determination of residual voltage at the end of integration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the integration time is extended to improve measurement accuracy, then the measurement precision is improved, but the integration time increases
Solution Approach 1:
The patent applies preliminary action by performing a calibration measurement before the actual light intensity measurement. During calibration, the integrator is charged to a known reference voltage level using a reference current source, establishing a baseline that accounts for residual voltages and circuit characteristics. This preliminary calibration enables accurate measurement with shorter integration times because the subsequent measurement only needs to capture the additional voltage change during the actual measurement interval, rather than requiring a long integration time to build up a large signal from scratch.
2Measurement precision
If a high gain factor is used to improve accuracy at low signal counts, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent uses preliminary calibration to determine circuit characteristics including the effective gain of the integration circuit. By measuring the relationship between reference current and resulting voltage during calibration, the system characterizes the actual gain without requiring theoretical calculations or complex calibration procedures. This measured gain information is then used to accurately convert measurement voltages to light intensity values, achieving accurate low signal count measurements with simple linear conversion rather than requiring complex high-gain amplification circuits.
Solution Approach 2:
The patent replaces the need for complex high-gain amplification hardware with a software-based solution. Instead of using high-gain operational amplifiers or specialized low-noise amplification circuits to boost weak signals, the system uses digital processing of the integration time measurement results. The calibration-derived gain factor is applied as a multiplication factor in software to convert the measured integration time (proportional to voltage change) to light intensity, achieving the same effect as hardware gain but with simpler, more flexible digital circuitry.
3Productivity
If the integration time is reduced to improve productivity, then the productivity is improved, but the measurement precision deteriorates
Solution Approach 1:
The patent enables reduced integration times while maintaining precision by performing preliminary calibration that characterizes the integration circuit's behavior. The calibration establishes the relationship between integration time and light intensity based on known reference measurements. Once calibrated, the system can use short integration times because the calibration data provides the scaling relationship needed to accurately interpret even small voltage changes. This eliminates the need for long integration times to amplify weak signals, allowing fast measurements without sacrificing accuracy.
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 enhances accuracy at low signal counts without requiring high gain factors, enabling reduced integration times and improved light intensity measurement.
Implementation Method 1
a photodiode having a photodiode output for providing a current
Implementation Method 2
an integrator having an integrator input selectively coupled to said photodiode output for receiving said current and an integrator output for providing an integrated output voltage
Data Source
AI summary
A method of measuring light intensity comprising exposing a photodiode to light to cause the photodiode to provide a current of a first polarity, supplying said current to an integrator to integrate said current to provide an integrated output voltage, and comparing the output voltage with a threshold voltage. Charge packages of opposite polarity are applied to said first polarity to reset the integration voltage prior to the start of the integration time. At the end of the integration time, the photodiode is disconnected from said integrator and a reference voltage coupled to the integrator input, whilst a resistance is coupled into the circuit until the comparison signal switches. The comparison signal is monitored to measure a time between the end of the integration time and the switching of the comparison signal to provide a measure of a residual voltage.