Ch 6: Photodiodes and Optical Sensors Flashcards
Q: What is a photodiode?
A: A semiconductor device that converts light into an electrical current.
Q: What is the photovoltaic mode of a photodiode?
A: A mode where the photodiode generates voltage in response to light without external bias.
Q: What is the photoconductive mode of a photodiode?
A: A mode where the photodiode operates with reverse bias to increase sensitivity and speed.
Q: What is responsivity in optical sensors?
A: The ratio of output electrical signal to input optical power, measured in A/W (amperes per watt).
Q: How does a phototransistor differ from a photodiode?
A: A phototransistor amplifies the current generated by light, providing higher output signals.
Q: What is a solar cell?
A: A large-area photodiode designed to convert sunlight into electrical energy.
Q: What is the dark current in a photodiode?
A: The small current that flows through the photodiode in the absence of light.
Q: What are avalanche photodiodes?
A: Highly sensitive photodiodes that use avalanche multiplication to amplify the signal.
Q: What is spectral response?
A: The range of wavelengths a photodiode can detect effectively.
Q: Define quantum efficiency in optical sensors.
A: The ratio of the number of charge carriers generated to the number of incident photons.
Q: What is a fiber optic sensor?
A: A sensor that uses optical fibers to transmit light and measure physical parameters.
Q: What is total internal reflection in optical sensors?
A: A phenomenon where light is completely reflected within a medium, used in fiber optics.
Q: How are LEDs used in optical sensors?
A: As light sources to illuminate the target or medium being measured.
Q: How does a photodiode array work?
A: It consists of multiple photodiodes used to detect spatial distribution of light.
Q: What is the primary use of LDRs (light-dependent resistors)?
A: To detect light intensity in applications like night lighting.
Q: What is a laser diode?
A: A diode that emits coherent and monochromatic light, used in precision applications.
Q: What are the applications of optical sensors?
A: Used in imaging, communications, and environmental monitoring.
Q: How does light intensity affect a photodiode?
A: Higher light intensity increases the current generated.
Q: What is an optical encoder?
A: A device that uses optical sensors to measure position or motion.
Q: What is the use of a beam splitter in optical systems?
A: To divide a beam of light into two or more separate beams.
Q: How do optical sensors contribute to biosensing?
A: By detecting changes in light absorption or reflection due to biological interactions.
Q: What is a spectrophotometer?
A: An instrument that measures the intensity of light as a function of wavelength.
Q: Define optical density.
A: The logarithmic measure of light absorption by a sample.
Q: What are near-infrared sensors used for?
A: Detecting wavelengths just beyond the visible spectrum, often for biological applications.
Q: What is a CCD sensor?
A: A charge-coupled device used to capture images by converting light into electronic signals.
Q: How does a PN photodiode generate current in photoconductive mode?
A: By creating a photocurrent proportional to light intensity.
Q: How can a PN photodiode reduce high-frequency noise?
A: By adding a low-pass filter in parallel with the feedback resistor in the gain stage.
Q: What is the resistor value needed for a gain of 2000 in a PN photodiode circuit?
A: 200 kΩ.
Q: Why does a phototransistor lack a base prong?
A: Incoming photons act as base currents.
Q: What capacitor value attenuates signals above 1 kHz in a gain stage?
A: 0.8 nF.
