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TDC 311 - PowerPoint PPT Presentation

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.

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TDC 311

Basic Electronic Circuits

• 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)

• 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

• All systems experience resistance (R).

• Ohm’s Law: V = I*R where R = Ohms (Ω)

• or R = V / I

• As temperatures increase in metal, resistance increases. In semiconductors, resistance generally decreases. (Figures 3 and 4)

• 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)

• 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)

• 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

• 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).

+

-

Emitter (N)

Base (P)

Collector (N)

Microphone

Figure 8

Speaker

Base P blocks flow from emitter to collector.

Need to add a wire from base so electrons have some place to flow.

+

-

Microphone

Speaker

Figure 9

• 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)

• 1GB flash drive

• 230 bits (about 1 billion)

• Each bit requires 2 transistors

• About 2 billion transistors

• Semiconductors are approaching fundamental physical size limits

• Technologies that may improve performance beyond semiconductor limitations

• Optical processing

• Hybrid optical-electrical 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

• 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)

• 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?

• 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?

• 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.

• 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

• 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*NumTurns2*AreaOfCoil*m) /

(LengthOfCoil * 10,000,000)

where m=permeability of core (air=2; steel=2000)

• Common application area: traffic signals

• 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)

• 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)

• 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.

• 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.

• 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)

• 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

• 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

• 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