# TDC 311 Basic Electronic Circuits. Voltage A battery / generator has + and - posts. Electrons flow through a circuit from the - post to the + post. The.

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TDC 311 Basic Electronic Circuits

Voltage A battery / generator has + and - posts. Electrons flow through a circuit from the - post to the + post. The potential difference between the two posts is V, voltage. V is the push of electrons. The higher the voltage, the higher the push. (Figures 1 and 2)

Current The current (I) is the charge passing through a given cross section of wire per unit time: I = Δ Q / Δ t = charge / time Consider a hose versus a fire hydrant. The direction of a current is in the direction of positive charge motion. Since only electrons (the negative charge) move within metal, the direction of current is opposite the flow of electrons. For example  House current  Typical CPU  Lightning strike

Resistance All systems experience resistance (R). Ohm’s Law: V = I*Rwhere R = Ohms (Ω) or R = V / I As temperatures increase in metal, resistance increases. In semiconductors, resistance generally decreases. (Figures 3 and 4)

Watt The measure of electric work and power is the watt. Power = V*I A current of 0.50 A flows through a 200 ohm resistor. How much power is lost in the resistor? (Expression 1)

AC and DC All above examples are direct current (DC). The push of electrons is always in one direction. AC - alternating current: The push of electrons is first from one direction and then from the opposite direction, over and over. (Figure 5)

Two ways to control power 1. Control the amount of power put into the circuit (harder to do) 2. Control the power at some point other than at the source (more common). ( Figure 6) Then we can switch it on or off, or regulate/vary the resistance. Circuits are made of hundreds / thousands /... of points that need switching and regulating. What device does this? A vacuum tube? Yes, but something better

Transistor The transistor is made of either germanium or silicon and has three distinct sections (Figure 7) The NPN transistor can act as a variable resistor or as a switch (conduct current, throttle it partially, or block it entirely).

Consider the following circuit Microphone Figure 8 Emitter (N) Base (P) Collector (N) Speaker + - Base P blocks flow from emitter to collector. Need to add a wire from base so electrons have some place to flow.

More appropriate figure Microphone Speaker + - Figure 9

Basic logic gates How were relays used to create basic logic gates? (Figures 11 and 12) How are transistors used to create basic logic gates? (Figures 13 and 14)

Equivalent Transistors

Consider the numbers 1GB flash drive 2 30 bits (about 1 billion) Each bit requires 2 transistors About 2 billion transistors

Future Trends Semiconductors are approaching fundamental physical size limits Technologies that may improve performance beyond semiconductor limitations  Optical processing  Hybrid optical-electrical processing

Optical Processing Could eliminate interconnection and simplify fabrication problems; photon pathways can cross without interfering with one another Eliminating wires would improve fabrication cost and reliability Not enough economic incentive to be a reality yet

Electro-Optical Processing Devices provide interface between semiconductor and purely optical memory and storage devices  Gallium arsenide (both optical and electrical properties)  Silicon-based semiconductor devices (encode data in externally generated laser light)

Inductor An inductor is basically a coil of wire. While it looks simple, it has some interesting properties (Figure 15) If you remove the inductor from the circuit, this is just a flashlight. What happens when you insert the inductor into the circuit?

Inductor When you close the switch, the bulb burns brightly and then gets dimmer. When you open the switch, the bulb burns brightly, then quickly goes out. Why?

Inductor The wire in the coil (inductor) has less resistance than the light bulb. But the coil wants to build up a magnetic field. While the field is building, the coil inhibits the flow of current. Once the field is built, the current can flow normally through the coil. When the switch is opened, the magnetic field around the coil keeps current flowing in the coil until the field collapses. This keeps the bulb lit for a short period of time after the switch is open.

Inductor The capacity of an inductor is controlled by four factors:  number of turns of wire  material the coils are wrapped around  cross-sectional area of the coil  length of the coil

Inductor Putting iron in the core of an inductor gives it much more inductance than air would. The standard unit of inductance is the henry: H=(4*pi*NumTurns 2 *AreaOfCoil*m) / (LengthOfCoil * 10,000,000) where m=permeability of core (air=2; steel=2000) Common application area: traffic signals

Capacitor A capacitor is a little like a battery. It holds a charge, but only for a brief moment. A capacitor has two metal plates separated by a dielectric (such as air, paper, plastic, or anything else that does not conduct electricity). What happens when you connect a capacitor to a battery? (Figure 16)

Capacitor Once the capacitor is charged, it has the same voltage as the battery. Let’s hook up a capacitor, a battery, a bulb, and a switch in the following fashion: (Figure 17)

Capacitor When the switch closes, the light bulb lights up as current flows from the battery to the capacitor and the capacitor charges up. The bulb gets progressively dimmer and finally goes out once the capacitor reaches it full charge. When you open the switch, the light bulb brightens momentarily and then dims and goes out. The capacitor is now discharged.

Capacitor The farad is the unit of capacitance. A farad is one coulomb (6.25e 18 electrons) of charge at 1 volt. That is a lot of charge! Most capacitors are rated in microfarads. Common capacitor applications include storing charges for high speed use, such as in a flash of a camera. Capacitors can also smooth (eliminate) ripples in current. A capacitor can block DC voltage and let AC voltage through.

Diode A diode is a simple device that allows electrons to flow in one direction only (Figure 18) Diodes can be used to make sure current flows in one direction only, so if you put your batteries in backwards, it does not ruin your electronic device. Diodes can also be used to smooth out AC voltages (Figure 19)

Serial vs parallel circuits Circuits can be either serial or parallel. Serial circuits: Figures 20 and 21 For example, resistors in series add directly Parallel circuits: Figure 22 Resistors in parallel: add their reciprocals and take reciprocal of total

Magnetic Fields and Wires Oersted discovered that currents in wires produce magnetic fields. Right-hand rule: Grasp wire with thumb pointing in direction of current. Fingers point in direction of magnetic field. Furthermore, a changing magnetic field passing through a wire will induce a current in that wire. Crosstalk

Memristor? Concept introduced in a paper in 1971; first memristor created in lab April 30, 2008 First basic element since resistor, capacitor and inductor Very small; can hold a 1 or 0 with or without power Can be fashioned into non-volatile solid state memory 100 gigabits in a square centimeter at one tenth the speed of DRAM

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