Unit 2. Electronic circuits and logic families Digital Electronic Circuits (Circuitos Electrónicos Digitales) E.T.S.. nformática Universidad de Sevilla Sept. 23 Jorge Juan <jjchico@dte.us.es> 223 You are free to copy, distribute and communicate this work publicly and make derivative work provided you cite the source and respect the conditions of the AttributionShare alike license from Creative Commons. You can read the complete license at: http://creativecommons.org/licenses/bysa/3. Departamento de Tecnología Electrónica Universidad de Sevilla Contents Electronic circuits Logic families Departamento de Tecnología Electrónica Universidad de Sevilla
Contents Electronic Circuits Conductors and charge carriers Electronic devices Electric circuits Semiconductors and semiconductor devices Technology: discrete devices and integrated circuits Logic families Bivalued digital circuits Logic gates and logic operators Logic families Electrical parameters Departamento de Tecnología Electrónica Universidad de Sevilla Conductors and charge carriers E Metal atoms Free electrons Conductors charge carriers can be positive () or negative () Most typical charge carriers are free electrons () in metals. When an electric field (E) is applied, electrons move accordingly. Electric fields exist whenever an electric potential difference (voltage) is applied. Departamento de Tecnología Electrónica Universidad de Sevilla
Basic conductor properties Conductors in electrical circuits Electric magnitudes in circuits: Typically wireshaped Charge (and electric field) is confined inside the conductors oltage: potential difference between two points in the circuit (olts []). Current: charge per unit time crossing the conductor's section (Amperes [A]). Charge does not accumulate inside conductors: conductors remain neutral. = 2 2 dq d = 2 = Departamento de Tecnología Electrónica Universidad de Sevilla Ohm's Law Ohms law Resistance: relation between the voltage and current across the conductor. Unit: Ohms [Ω]=[]/[A] deal conductors (R=) Wires: metals used for connection in electronic circuits can be considered ideal conductors most of the time Same voltage across wires 2 2 = 2 = R= 2 R= = 2 Departamento de Tecnología Electrónica Universidad de Sevilla
Devices 2 A 2 2 B Electronic elements with two or more terminals mpose a relationship between the current and voltage across the terminals Net charge is not accumulated inside the devices C 3 23... = 3 2 3 4 Departamento de Tecnología Electrónica Universidad de Sevilla Basic electronic devices Resistor = R Capacitor Farad [F] =C d dt nductor Henry [H] = L d dt Departamento de Tecnología Electrónica Universidad de Sevilla
Basic devices: ideal sources Constant voltage source (power supply) (battery) CC = CC CC t ariable voltage source S = S t S t S ariable current source = S t S t Departamento de Tecnología Electrónica Universidad de Sevilla Electric circuits Connection of devices with wires to achieve some properties or functionality. Node: connection between two or more devices. Same voltage along a single node (ideal wire) S R R2 out oltage divider R S C out Lowpass filter Departamento de Tecnología Electrónica Universidad de Sevilla
Circuit analysis Circuit analysis is based on: Kirchhoff laws Algebraic solution Transient analysis: consider variations with time. Current: the sum of the currents entering a circuit node is ero (charge does not accumulate in circuit nodes) The sum of voltage drops along any close path is ero. Static analysis (DC analysis): assumes all the circuit sources and magnitudes are constant. Device equations Topological Equations (Kirchhoff laws) Differential equations AC analysis: solves the stationary state when signal are sinlike Uses special mathematical tools (Laplace transform) Departamento de Tecnología Electrónica Universidad de Sevilla Circuit analysis. Example 5K 2 5 2K 2 3 K 3 K S S = R S C t out S S = t Departamento de Tecnología Electrónica Universidad de Sevilla
Power Consumed energy per unit time Power is a key point in current electronics. P= Portable devices Dissipation Environment Power is consumed (dissipated) every time some current goes from a higher to a lower potential. Power can be negative n this case, the device is "producing" power to be consumed in the circuit (e.g. power supply) Departamento de Tecnología Electrónica Universidad de Sevilla Semiconductor devices (intrinsic) T= T> Group atom (Si) Electron () bad conductor Hole () (left by the electron) Departamento de Tecnología Electrónica Universidad de Sevilla
Semiconductor devices (doped) (T=) ntype ptype good conductor good conductor Group athom (Si) Electron () Hole () (left by the electron) Group athom (P, As) Group athom (B, Ga) Departamento de Tecnología Electrónica Universidad de Sevilla Semiconductor nice properties Conductance depends on temperature, light, etc. Temperature sensors Light sensors Solar cells... Conductance can be controlled by doping Type of carrier can be controlled by doping Nice devices can be created by combining different types of semiconductors (PN) Departamento de Tecnología Electrónica Universidad de Sevilla
Semiconductor devices. Diodes LED p n /Ron on on.7 Departamento de Tecnología Electrónica Universidad de Sevilla Bipolar transistor C B E C Collector n p n Emitter n p n NPN B E Base C B E p n p E Collector p n p Emitter PNP B C Base B C C = B A small current through BE allows a big current to flow through CE. Direct use: amplifier. Departamento de Tecnología Electrónica Universidad de Sevilla
MOSFET transistor G S Conductor (PolySi) D Dielectric (SiO2) D n n nmos G p S G: gate S: source D: drain SS: substrate DS SS GS G S D D p p pmos A small voltage between G and S allows a big current to flow from D to S. G n S Direct use: amplifier. SS Departamento de Tecnología Electrónica Universidad de Sevilla Transistor demo K K >M? >M 5 5 >M 5?? D = R D R D R Departamento de Tecnología Electrónica Universidad de Sevilla
Technology Discrete components ntegrated circuits (chips, C's) Devices are fabricated one by one Normally, they are soldered in printed circuit boards Several devices (mostly transistors) are fabricated at the same time over a common substrate. Really big numbers: 5 million! devices in the same chip. Most of today's electronics is done as C's Types of C's Application specific Programmable Departamento de Tecnología Electrónica Universidad de Sevilla Discrete devices http://en.wikipedia.org/wiki/file:splatine.jpg Departamento de Tecnología Electrónica Universidad de Sevilla
ntegrated circuits http://en.wikipedia.org/wiki/ntegrated_circuit Departamento de Tecnología Electrónica Universidad de Sevilla ntegrated circuits. Evolution Gordon Moore (964): ntegration density doubles every 8 months. Departamento de Tecnología Electrónica Universidad de Sevilla
ntegrated circuits. Types Application Specific (ASC) Configurable (e.g. FPGA) Pentium 4 2 (42M ttores) http://commons.wikimedia.org/wiki/file:fpga_xilinx_spartan.jpg Cell 26 (234M ttores) http://commons.wikimedia.org/wiki/file:fpgaa.gif Departamento de Tecnología Electrónica Universidad de Sevilla Logic families Bivalued digital circuits Logic gates and logic operators Logic families Electrical parameters Departamento de Tecnología Electrónica Universidad de Sevilla
Digital Circuit: 's and 's X Analog t X 2 2 Digital (5 values) t Sequence:,, 2, 2,, 2, 2,, X Digital (2 values) t Sequence:,,,,,,,, Departamento de Tecnología Electrónica Universidad de Sevilla Digital Circuit in Digital electronic circuit out Departamento de Tecnología Electrónica Universidad de Sevilla
Logic gates. CMOS inverter Logic gates perform operations on digital data. The simplest (non identical) operation is inversion, implemented by the inverter gate. CC in out in = out = CC CC in out CC in out in = CC out = Departamento de Tecnología Electrónica Universidad de Sevilla Twoinput logic functions x F y F xy F F F2 F3 F4 F5 F6 F7 F8 F9 F F F2 F3 F4 F5 n general, there are 2(2^n) functions of n variables Departamento de Tecnología Electrónica Universidad de Sevilla
Common logic gates AND NAND OR NOR x y x y x y x y xy xy xy xy =x y =x y =xy =xy Departamento de Tecnología Electrónica Universidad de Sevilla Common logic gates XOR OR XNOR x y x y xy xy =x y =x y ery useful in arithmetic blocks like adders Departamento de Tecnología Electrónica Universidad de Sevilla
Sample CMOS implementation x y n CMOS gates are "naturally" inverting. Noninverting gates are obtained by combining inverting gates. CC x y Departamento de Tecnología Electrónica Universidad de Sevilla Sample CMOS implementation x y CC x y Departamento de Tecnología Electrónica Universidad de Sevilla
Logic families Logic gates are fabricated using different technologies (Bipolar, CMOS, ) and different techniques. Logic family: set of gates sharing the same technology and similar design techniques Some logic families are compatible among them Gates in a family are compatible: will operate correctly when connected to each other. Share similar electrical and dynamic parameters. E.g. 74 series (Bipolar TTL) and 74HC (CMOS) Specially relevant when working with SS and MS devices Should only combine chips of the same family/series E.g. 74 series Departamento de Tecnología Electrónica Universidad de Sevilla Logic families Bipolar ECL (Emittercoupledlogic): first logic family available in integrated circuits (962) TTL (Transistortransistor logic): very popular. Many improvements since 963. E.g. 74 series CMOS LS TTL: very popular lowpower variant E.g. HC logic. Compatible with TTL. E.g. 74HC series Most extended technology nowadays. Better noise margins, lower static consumption, cheaper, but slower. BiCMOS Combines CMOS inputs with TTL drivers Provides various logic families Departamento de Tecnología Electrónica Universidad de Sevilla
Logic families 74 series ery popular as SS and MS devices in education nitially a TTL family, there exist various compatible logic families in various technologies. Departamento de Tecnología Electrónica Universidad de Sevilla Electrical parameters Departamento de Tecnología Electrónica Universidad de Sevilla
Electrical parameters Noise margins in out out out CC OH OH NMH H L CC OL OL in in out L H NML CC in noise NML = L OL NMH = OH H NM = min(nml, NMH) Departamento de Tecnología Electrónica Universidad de Sevilla Electrical parameters Supply voltage (CC): minimum, maximum and nominal supply voltage a gate can tolerate. Maximum input current (L, H): current in the input terminal for low and high inputs. Maximum output current ( OL, OH): max. current the gate can provide at the output without degrading the logic level (both low and high outputs). Small is good. Big is good. Determines the maximum fanout. Power consumption Static Dynamic: depends on the frequency Departamento de Tecnología Electrónica Universidad de Sevilla
Electrical parameters CC O O > N x N FANOUT Maximum value of N so that O > N x in both cases (high and low output levels) Departamento de Tecnología Electrónica Universidad de Sevilla Switching parameters Transition time: time for a transition to change from: % CC to 9% CC (rising transition): t LH 9% CC to % CC (falling transition): t HL Depends on many factors, specially gate's strength and load. Propagation delay: time elapsed from the input transition to the output transition. Both lowtohigh and hightolow: t plh, tphl. 5% CC as a reference Depends on many factors, specially the output load (linear) Departamento de Tecnología Electrónica Universidad de Sevilla
Switching parameters in out tplh CC.9xCC out.5xcc in.xcc thl t Larger propagation delays make digital systems (computers) to run slower (smaller clock frequency) Departamento de Tecnología Electrónica Universidad de Sevilla