An electronic circuit extracts a ratio of currents from two sources and provides an output that is a function of the current ratio. An embodiment of the circuit includes a source current that may be provided by a blue-green photodetector and a sinking current that may be provided by a red photodetector. The source current feeds the input of a current splitter formed by a pair of PFETs. A portion of the source current is fed from the current splitter to a current ratio extractor implemented in CMOS. The remaining portion of the current from the current splitter is fed to a node shared with the sinking current and a second input to the current ratio extractor. The current ratio extractor produces an output voltage that is a function of the ratio of the photodiode currents and is substantially independent of the total current. The output voltage provides color information that may be used in low-cost machine vision systems for tasks such as sorting objects based on color or detecting object boundaries while rejecting shadows and reflective glints.

Current ratio circuit for multi-color imaging

In an X-ray analysis apparatus provided with a detector comprising photodiode-detection elements, it is possible to eliminate the dark current and the background current from the measurement signals due to the fact that elements in the signal reading device can be combined Due to the fact that also during the measurement at a stationary peak beside the signal amplitude also signal ratios can be obtained from combinations of detector elements, the correct position and amplitude of the peaks to be measured can be determined The detector can also be provided with mutually separated detector elements which have such a surface area and configuration that the dark current can already be conpensated thereby

X-ray analysis apparatus

The current-voltage converting circuit converts an input current signal into a voltage signal, and the single-differential converting circuit converts the voltage signal into differential signals so as to output the differential signals. The first and second low-pass filters input outputs from the single-differential converting circuit, respectively, and the voltage-current converting circuit converts a difference between the output voltages from the first and second low-pass filters into a current signal. The current-voltage converting circuit inputs a voltage held in the hold capacitor as a control signal and converts the input current signal into a voltage signal using a current-voltage converting gain according to the control signal.

Optical receiving circuit

A method for measuring and monitoring the biological effects of UV-B radiation along with an instrument for implementing this method. The biological UV-B effect monitor generally includes a first photodetector sensitive to UV-B only, a second photodetector sensitive to visible light only, and a microprocessor for normalizing the UV-B response relative to the visible response and applying one or more stored biologic response algorithms to the measured and normalized UV-B value to produce a biologic response output signal.

Biological uv-b effect monitoring instrument and method

A multipurpose all-wavelength intensity monitor for determining and monitoring the output intensity of ultraviolet sources The unit measures ultraviolet wavelengths of 365 nanometers, 300-312 nanometers, and 254 nanometers without changing sensors or switches and the monitor is based on measurement utilizing a time period with a precalibrated microjuole setting The intensity is determined by measuring the time period elapsed from the beginning of the monitoring to a tone sound which indicates the end of the monitoring period This time period is compared to a chart with a curve for each of the ultraviolet wavelengths Using the curve with the known time elapsed will indicate the intensity output The monitor indicates loss of intensity by comparing lengthening of the monitored time or by indicating the actual intensity using the time output curves A modified stopwatch can start the timing when unit is actuated and stop the timing when tone is sounded

All wavelength ultraviolet intensity monitor

A photodetector apparatus is provided having an output only when exposed to electromagnetic radiation above or below a specified cut-off frequency. At least first and second light sensor means produce electrical signals responsive to electromagnetic radiation of first and second overlapping frequency ranges, respectively, and peak electrical responses at different first and second peak frequencies, respectively. Electrical means compare the electrical signals from at least said first and second light sensor means and produces an electrical signal preferably of only one polarity and equal to a product of a first constant times the amplitude of the electrical signal produced by said first light sensor means minus a product of a second constant times the amplitude of the electrical signal produced by said second light sensor. The apparatus is particularly useful in ultraviolet detection where the sensor means are comprised of separate silicon carbide semiconductor bodies each containing a PN junction.

Photodetector apparatus with a zero cut-off response to absolute zero at a specified light frequency

The invention is an electronic current to voltage converter circuit including a temperature compensating circuit, a differential amplifier circuit, a feedback circuit, and an input voltage zero adjust circuit for establishing and maintaining the input voltage signal to the circuit substantially zero to permit virtual short circuit current measurements of signals developed by a current generating device.

Wallace D Loftus

Papers

Photodetector apparatus with a zero cut-off response to absolute zero at a specified light frequency

Electronic current to voltage converter

Single pulse generator