ECE 03 Midterm 1 PDF

ECE 03 – ELECTRONICS 3: ELECTRONICS SYSTEM & DESIGN BSECE III ENGR. JOEL ANTHONY L. SEVILLA OCTOBER 2024 OPTOELECTRONICS Study and application of electronic devices and systems that find, detect, and control light, usually considered a sub-field of photonics....

ECE 03 – ELECTRONICS 3: ELECTRONICS SYSTEM & DESIGN BSECE III ENGR. JOEL ANTHONY L. SEVILLA OCTOBER 2024 OPTOELECTRONICS Study and application of electronic devices and systems that find, detect, and control light, usually considered a sub-field of photonics. Also called optronics. Based on the quantum mechanical effects of light on electronic materials, especially semiconductors, sometimes in the presence of OPTOELECTRONICS electric fields. Deals with the optical interaction on the electronic responses in some specific optically active semiconducting materials. Electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices in their operation. OPTOELECTRONICS Normally they are semiconductor devices. Operation is based on the wave theory and quantum mechanics (photoelectric effect). OPTICAL ENERGY OPTOELECTRIC ELECTRICAL (LIGHT) DEVICE ENERGY Light may be generally described as electromagnetic radiation. Quantum Theory states that light consists of discrete packets of energy called photons. E = hf where: h = Planck's constant (6.624 x 10¯³⁴ J-s) E = photon energy in Joules (J) f = frequency of light in Hertz (Hz) λ = c/f where: λ = wavelength of light in meters (m) c = speed of light (3 x 10⁸ m/s) If we will equate both formulas: E = hf = hc/λ λ = hc/E If E is in electron-volt (eV), then since 1 eV = 1.6 x 10¯¹⁹ J (6.624 x 10¯³⁴ J-s) (3 x 10⁸ m/s) λ= (E * 1.6 x 10¯¹⁹J) λ = 1.242/E μm  Electromagnetic Spectrum Table Infrared Light 300 – 3000 GHz Infrared Light 3 – 30 THz Infrared Light 30 – 300 THz Visible Light 0.3 – 3 PHz Ultraviolet Light 3 – 30 PHz Visible Light spectrum is divided into several colors, the commonly associated with industrial process control is diffused or white light which is a mixture of virtually all colors within the visible spectrum. Red – lowest frequency, longest wavelength Violet – highest frequency, shorter wavelength Infra – latin term for under or below Ultra – latin term for beyond 1 micron = 1 μm = 1 x 10¯⁶ m 1 Angstrom = 1 Å = 1 x 10¯¹⁰ m (used in measuring wavelengths of light) White light is produced by conventional light bulbs, may also be referred to as incandescent light, it is produced by sources that must become hot prior to radiating energy. Incandescent – latin incandescere, meaning to become hot and glow. Incandescent light/ white light - produces heat. IR & UV radiation - produces virtually no heat. Incandescence - ability of a material to radiate light as a result of being heated. Phosphorescence – defined as the ability of a material to emit light both during & after exposure to radiation. Phosphorescent material is actually ionized by the radiation source. Fluorescence – defined as the ability of a material to emit light during exposure to radiation. With fluorescence materials, luminescence occurs only while a source of radiation is actually present. Visible light – used in bar code readers, QR codes and video acquisition systems IR light - used in the operation of industrial light barriers & photo sensors found in automated conveyance systems UV light – used in barcode detection systems, designed to detect identifying marks or stamps in containers LIGHT EMITTING DIODE (LED) A semiconductor device that emits light when forward bias. Generally uses Gallium Arsenide Phosphide (GaAsP) and Gallium Phosphide (GaP). Light is produced as the electrons and holes are recombined and releases energy. LIGHT EMITTING DIODE (LED) TOP VIEW SIDE VIEW LED max forward voltage = 1.2 V to 3.2 V depending on the device LED reverse breakdown voltage = 3 V to 10 V The amount of power output translated into light is directly proportional to the forward current. LED biasing and characteristic curve LED APPLICATIONS burglar-alarm systems solid-state video displays image sensing circuits fiber optics data links and remote controllers seven segment displays numeric displays SEVEN-SEGMENT DISPLAY Consists of 7 rectangular LEDs which can form alphanumeric figures. LED segments are labelled 'a' to 'g' In common-cathode type, all the cathodes of the diodes are tied together. In common-anode type, all its anodes are tied together to +5 volts and ground is used to light the individual segments SEVEN-SEGMENT DISPLAY Example: to light number 5, segments a, f, g, c, and d must be forward-biased; only 5 volts is to be applied to the anode of these segments to light them. SEVEN-SEGMENT DISPLAY TWO-COLOR LEDs When leads R and C are forward-biased, the LED emits red light. When leads G and C are forward-biased, LED emits green light. THREE-COLOR LEDs It has two leads that acts as both anode and cathode. When dc current flows through one direction, it emits red light, but when the current flows in the opposite direction, the LED emits green light. With ac current, yellow light is given out. BLINKING LEDs Combination of an oscillator and an LED in one package. Looks like an ordinary LED. Blinking frequency is usually 3 Hz when the diode forward bias is 5 V. Conducts about 20 mA of current when ON and 0.9 mA when OFF. LIQUID CRYSTAL DISPLAYS (LCD) The background is either light or dark, when a voltage is applied to a segment, then the alphanumeric display is visible. The amount of voltage necessary for display varies depending on the type of display, from 2 to 20V. Low power LCDs require less power than LEDs. But LEDs have faster response times and longer life. A liquid crystal is a material (usually an organic compound) which flows like a liquid at room temperature but whose molecular structure has some properties normally associated with solids. A thin layer of liquid crystal is transparent to incident light. When light falls on an activated (exposed to electricity) layer of a liquid crystal, it is either absorbed or else is scattered by the disoriented molecules. LCD Construction A liquid crystal 'cell' consists of a thin layer (about 10 um) of a liquid crystal sandwiched between two glass sheets with transparent electrodes deposited on their inside faces. With both glass sheets transparent, the cell is known as transmitive type cell. LCD Construction When one glass is transparent and the other has a reflective coating, the cell is called a reflective type. The LCD does not produce any illumination of its own. It depends entirely on illumination falling on it from an external source for its visual effect. Operating Condition When field-effect display is energized, the energized areas of the LCD absorb the incident light and hence, give a localized black display. When dynamic scattering display is energized, molecules of energized area of the display become turbulent and scatter light in all directions. The activated areas take on a Operating Condition frosted glass appearance resulting in a silver display. The un-energized areas remain translucent. ADVANTAGES Extremely low power requirement, about 10 - 15 μW per 7-segment display as compared to a few mW for an LED. Lifetime of about 50,000 hours (around 5.7 yrs) watches and portable instruments (field-effect LCDs). USES picture elements (pixels) of the screen in one type of B&W TV desktop LCD monitors notebook computer display cellular phone display PHOTODIODE The photodiode is a semiconductor pn junction device whose region of operation is limited to the reverse-bias region. The dark current refers to the current that flows when no light is incident. A photodiode can turn its current ON and OFF in nanoseconds; it is one of the fastest photodetectors. Symbols and commercially available components APPLICATION Instrumentation circuits as a sensor Alarm system sensor Detection of objects on a conveyor belt Photodiode used in alarm system and conveyor PHOTOCONDUCTIVE CELLS A photoconductive cell varies resistance with the intensity of light. Like a common resistor, a photoconductive cell has no polarity and can be placed into the circuit in either direction. PHOTOCONDUCTIVE CELLS Generally made of cadmium compounds such as cadmium sulphide (CdS) and cadmium selenide (CdSe). Spectral response of CdS cell is similar to the human eye hence it is often used to simulate the human eye. Working Principle Typically, the dark resistance of the cell is 1 MΩ or larger under illumination, the cell resistance drops to a value between 1 and 100 kΩ depending on surface illumination. aka Photo cells, Photo resistors, Photo resistive device, & light detecting resistor. Photoconductive materials most frequently used: Cadmium Sulfide (CdS) = 5100 Å Cadmium Selenide (CdSe) = 6150 Å Response time CdS = 100 ms CdSe = 10 ms APPLICATIONS inexpensive and simple detector which is widely used in OFF/ON circuits, light measurement, and light-detecting circuits. PHOTOTRANSISTOR Light-sensitive transistor and is similar to an ordinary BJT except that it has no connection to the base terminal. Its operation is based on the photodiode that exists at the CB junction. PHOTOTRANSISTOR Instead of the base current, the input to the transistor is provided in the form of light. Silicon NPNs are mostly used as phototransistors. Device is usually packed in a TO-type can with lens on top although it is sometimes encapsulated in clear plastic. When there is no incident light on the CB junction, there is a small thermally generated collector-to-emitter current ICEO which, in this case, is called dark current and is in the nA range. When light is incident on the CB junction, a base current Iλ is produced which is directly proportional to the light intensity. Ic = βIλ Applications are similar to those of a photodiode. Main differences are in the current and response time. Its advantages are greater sensitivity and current capacity than photodiodes. However, photodiodes are faster, switching in less than a nanosecond. SOLAR CELLS Solar cells produce a voltage when subjected to light energy. The greater the light intensity, the greater amount of voltage produced. Solar cells act like a battery when connected in series or parallel. CHARACTERISTICS Operates with fair efficiency. Has unlimited life. Can be easily mass produced. Has a high power capacity per weight. PHOTO DARLINGTON In the photo darlington transistor configuration, the first transistor acts as the photodetector, and its emitter is coupled into the base of the second transistor. It has much greater sensitivity to incident radiant energy than a phototransistor because of higher current gain PHOTO DARLINGTON The switching time of 50ns is much longer than phototransistor or Photodiode. APPLICATIONS Light operated relay Dark operated relay IR EMITTERS Diodes that emit infrared radiation. IR emitter produce infrared radiation when forward biased. The higher the forward bias current, the greater the intensity of infrared radiation. The radiation pattern can vary from widely dispersed to a very narrow, focused beam. Applications Card readers Shaft encoders Intrusion alarms IR Transmitters LASER DIODE Laser diodes have a threshold level of current above which the laser action occurs but below which the laser diode behaves like a LED emitting incoherent light. It is coherent – there is no path difference between the waves comprising the beam. It is monochromatic – it consists of one wavelength and hence one color only. LASER DIODE It is collimated i.e. emitted light waves travel parallel to each other. A filter or lens is necessary to view the laser beam. APPLICATIONS used in variety of applications ranging from medical equipment used in surgery to consumer products like optical disk equipment, laser printers, hologram scanners etc. Laser diodes emitting visible light are used as pointers. Those emitting visible and infrared light are used to measure range (or distance). APPLICATIONS The laser diodes are also widely used in parallel processing of information and in parallel interconnections between computers. OPTICAL DISKS Used for reading or recording information and can be broadly divided into two groups: reading- only and recording-and-reading type. Optical disk equipment of either type make use of a laser diode, lenses and photodiodes. During recording, it changes electrical information into optical information and then records the information on the optical disk. OPTICAL DISKS During reading (or playback), the head optically reads the recorded information and changes the optical information into electrical information. Read only Optical Disk Equipment reads data from digital audio disks WORKING PRINCIPLE 1. Audio information (i.e. sound) is digitally recorded in stereo on the surface of a CD in the form of microscopic “pits” and “flats”. Read only Optical Disk Equipment 2. Light emitted from the laser diode passes through the lens and is focused to a diameter of about 1 μm on the surface of a disk. 3. As the CD rotates, the lens and beam follow the track under control of a servomotor. Read only Optical Disk Equipment 4. The laser light which is altered by the pits and flats along the recorded track is reflected back from the track through the lens and optical system to infrared photodiodes. 5. The signal from the photodiodes is then used to reproduce the digitally recorded sound. CD & DVD recording comparison LASER PRINTERS There are two types of optical sources usually used in printers; laser diodes and LED arrays. The printers using laser diodes are called laser beam printers (or simply laser printers). Words and figures can be printed rapidly and clearly more easily by a laser printer than by other types of printers. WORKING PRINCIPLE 1. Laser diode is driven by modulated signals from the computer. 2. The optical beam after passing through the lens is reflected by the rotating polygon mirror and scanned on the photosensitive drum. 3. At the developing unit, an electrically charged powder, called toner, is electrostatically attached to the written parts. WORKING PRINCIPLE 4. At the transcribing unit, the powder is transferred to the paper. Next, the transferred pattern is fixed by heating and pressing at the fixing unit. 5. Data from the computer is thus printed on the paper. Laser Printer Operation