Electromagnetic spectrum

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Rodney Damon Shelton
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1 Slide 1 Electromagnetic spectrum insert wavelengths of blue to red Optoelectronics 1

2 Slide 2 Electromagnetic spectrum E = hν = kt e E - Energy k - Plank s constant ν - frequency k - Boltzman s constant T e - equivalent temperature K Optoelectronics 2

3 Slide 3 Electromagnetic Spectrum slide deleted

Slide 4 Light-emitting diodes (LEDs) cathode anode anode p n cathode When electrons and holes combine in the depletion region the excess energy is given up in the form of a photon.

4 Slide 4 Light-emitting diodes (LEDs) cathode anode anode p n cathode When electrons and holes combine in the depletion region the excess energy is given up in the form of a photon. This energy is characteristic of the materials from which the junction is constructed and thus the photon always has the same wavelength. To emit photons the junction must be forward biased, and the wavelength as typically red, green, yellow, or in the infrared. The LED sits in a reflector and is covered by a plastic diffuser Optoelectronics 4

5 Slide 5 Light-emitting diodes (LEDs) simple LED,red, green, yellow, orange, or infrared. blinking LED, blinks 1-6 times per second. Can be used as a trivial oscillator. Simple means of creating numbers and characters. For numbers drive with 74HC4511. Tricolor LED, green one way, red the other Optoelectronics 5

6 Slide 6 viewing angle LEDs specs intensity forward voltage drop reverse breakdown max DC current max power LED type degrees color MCD V V ma mw NTE3000 indicator 80 red NTE3010 indicator 90 green NTE3026 tristate 50 red/gree 1.5/ /2.2 70/ n NTE3130 blinker 30 yellow NTE3017 infrared Notice that the forward voltage drop is not the 0.6 V we associate with a silicon diode, and that the reverse breakdown voltage is quite small Optoelectronics 6

7 Slide 7 LED operation Graphs produced with Mathematica Optoelectronics 7

8 Slide 8 LED Datasheet Optoelectronics 8

9 Slide 9 LED Datasheet Optoelectronics 9

10 Slide 10 voltage level sensor Some LED applications logic probe Vcc V in LED lights when the breakdown voltage of the zener is exceeded. The source must provide the current for the LED. A logic high turns on the Darlington pair and the LED. This is a high impedance measurement Optoelectronics 10

11 Slide 11 Tristate polarity indicator V in I r I g R 2 R 1 A tristate diode indicates the direction of DC current flow, or if the current is AC. The diode protects for reversed voltage breakdown and the resistors protect the tristate diode from voltage breakdown. positive current negative current AC current red green yellow Optoelectronics 11

Slide 12 Photoresistors insert figs and diagrams from data sheets. A photodiode is a light controlled resistor that operates much like a thermistor.

12 Slide 12 Photoresistors insert figs and diagrams from data sheets. A photodiode is a light controlled resistor that operates much like a thermistor. In an intrinsic semiconductor, photons can promote an electron to the conduction band leaving a hole in the valence band. This increase in carriers leads to a reduction in the resistance. Photoresistors are non-linear, slow (~100 ms) but cheap Optoelectronics 12

13 Slide 13 Photoresistor Specifications material energy gap (ev) wavelength (Å) CdS CdSe PbS PdTe PdSe Graphs produced with Mathematica Optoelectronics 13

14 Slide 14 Photoresistor applications Two simple circuits to switch a relay by the action of a photoresistor. Which one is on in the dark? on in the dark on in the light Optoelectronics 14

Slide 15 Photodiodes electric field diode current diode voltage When a photon of sufficient energy hits the semiconductor then an electron/hole pair is created.

15 Slide 15 Photodiodes electric field diode current diode voltage When a photon of sufficient energy hits the semiconductor then an electron/hole pair is created. The minority carrier then diffuses to the junction and an electric field is created. This electric field across the depletion zone is equivalent to a negative voltage across the unbiased diode. At left shows the increased negative offset as a function of increased light intensity Optoelectronics 15 Graphs produced with Mathematica

16 Slide 16 Characteristics of photodiodes The sensitivity of photodiodes is defined as, S = I diode P where P is the incident photon power per unit area. Typically S~2 µa/mw/cm 2. Silicon peaks at 900 nm in the infrared, and the sensitivity at 600 nm is down by ~60%. Diodes are faster than photoresistors, and a reverse bias speeds up the minority carrier diffuse and thus the response time (~ 1µs). I diode R V out V out = RI diode Optoelectronics 16

17 Go to the manufacturer s web site to obtain a datasheet of their product. Please follow these steps: 1. Go to the web site for Fairchild Semiconductor: 2. View the conditions of use for the web site by following the link on the home page called Site Terms & Conditions, or by following this link: 3. Return to the home page. 4. In the search box, enter the product number QSE773 into the search box, select Product Folders and Datasheets and click go. You want the datasheet for Plastic Silicon Pin Photodiode. 5. You will be presented with several options (download PDF, for example). Select how you would like to receive this datasheet.

18 Slide 19 Phototransistors, emitter p A phototransistor can be an npn bipolar transistor with a large base that does not have a lead. When photons hit the base they create electron/hole pairs, the electrons are drawn to the collector and the holes are filled with electrons from the emitter. Thus there is a current from the collector to emitter. n collector The dark current is typically ~0.1 µa with a light current of ~1 ma Optoelectronics 19

19 Go to the manufacturer s web site to obtain a datasheet of their product. Please follow these steps: 1. Go to the web site for Fairchild Semiconductor: 2. View the conditions of use for the web site by following the link on the home page called Site Terms & Conditions, or by following this link: 3. Return to the home page. 4. In the search box, enter the product number BPW36 or BPW37 into the search box, select Product Folders and Datasheets and click go. You want the datasheet for Hermetic Silicon Phototransistor. 5. You will be presented with several options (download PDF, for example). Select how you would like to receive this datasheet.

20 Slide 22 Uses of Phototransistors optical receiver tachometer Light reaching the phototransistor modulates the base of the bipolar transistor. The capacitor blocks current from the DC optical field. Once each rotation the slot in the disk permits light to reach the phototransistor which then shorts the output resistor. The output is counted for a fixed period of time to determine the rotation frequency Optoelectronics 22

21 Slide 23 Optoisolators Optoisolators can be used to provide isolation between components, to avoid ground loop problems, to control floating electronics, and to provide DC shifts Optoelectronics 23

22 Slide 24 1k 5V Optoisolators 5-12 V 4.7 k 1k 5V 5-12 V V out V out 4.7 k Which acts as an inverter? Optoelectronics 24

Figure 1: Diode Measuring Circuit

Figure 1: Diode Measuring Circuit Diodes, Page 1 Diodes V-I Characteristics signal diode Measure the voltage-current characteristic of a standard signal diode, the 1N914, using the circuit shown in Figure 1 below. The purpose of the back-to-back