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Properties of Digital Circuits Quantized States Voltage Transfer Characteristic (VTC) Voltage Levels Noise Margins Current Levels Fan-In and Fan-out Power Dissipation Propagation Delay Power-Delay Product IC Packaging Technology Trends of MOS Microprocessors and Memories ECE 3450 M. A. Jupina, VU, 2014 Some Key Lecture Objectives Before performing the Properties of Digital Circuits practicum, we need to look at the key properties of digital circuits used to compare one technology with another. How voltage levels of a technology not only define the logic states of a technology, but also lead to a definition of noise immunity for a technology. An understanding of how current levels, “loading,” power dissipation, and speed of operation are all inter-related. Reference: Fundamentals of Digital Logic, Chap 1, Sec 3.8, and App E.4. ECE 3450 M. A. Jupina, VU, 2014 Transistor-Transistor-Logic (TTL) TTL dominated the IC market from the 1960’s to early 1980’s. This picture changed in the 1980s due to two major factors: Discrete logic gates in static CMOS competitive in speed at a lower power cost. The advent of programmable logic components such as PLDs and FPGAs made it possible to program complex random logic functions (equivalent to hundreds of TTL gates) on a single component. This results in a large reduction in board real-estate cost, while adding flexibility. ECE 3450 became M. A. Jupina, VU, 2014 CMOS CMOS stands for Complementary Metal-Oxide Semiconductor. MOS field-effect transistors (nchannel and p-channel) are used to construct logic gates. FETs are voltage controlled and operate nearly as an ideal switch. MOSFETs advantages: Lower power consumption than BJTs so billons of devices can be packed onto a single chip (MOSFETs or what are now known as FinFETs have dimensions in the deep sub-micron range). ECE 3450 M. A. Jupina, VU, 2014 CMOS MOSFET Gate Length FinFET Gate Length Currently, how small is the gate length of a FinFET? ECE 3450 M. A. Jupina, VU, 2014 Quantized States Binary System possible states: 1 or 0, on or off positive logic: 1= high, 0 = low negative logic: 1= low, 0 = high Future Systems – multilevel logic Ex: if three different on-off levels, then 23 = 8 logic states ECE 3450 M. A. Jupina, VU, 2014 VTC of a TTL Inverter Vi Vo Voltage Levels (VOH, VOL, VIL,VIH) are defined at dVo/dVi = -1 ECE 3450 M. A. Jupina, VU, 2014 VTC for a CMOS Inverter Vout V OH = V DD Slope = –1 V OL = 0 V VT V IL V IH V ECE 3450 ( V DD – V T ) V DD Vin M. A. Jupina, VU, 2014 Table of Voltage Levels for TTL Families ECE 3450 M. A. Jupina, VU, 2014 PSPICE Schematic of LS7404 TTL Inverter ECE 3450 M. A. Jupina, VU, 2014 PSPICE VTC Simulation of the LS7404 ECE 3450 M. A. Jupina, VU, 2014 PSPICE VTC Simulation of the LS7404 VIL = 0.7 V VIH = 1.18 V VOH = 4 V VOL = 0.15 V ECE 3450 M. A. Jupina, VU, 2014 Digital Properties Practicum Measured VTC of LS7404 ECE 3450 M. A. Jupina, VU, 2014 Voltage Level Definitions VIH – High Level Input Voltage Vinput ≥ VIH to be recognized as a “1” TTL Ex: ECE 3450 VIH = 2V, thus at the input a “1” is between 2V and VCC M. A. Jupina, VU, 2014 Voltage Level Definitions VOH – High Level Output Voltage TTL Ex: ECE 3450 VOH = 2.4V, thus at the output a “1” is between 2.4V and VCC M. A. Jupina, VU, 2014 Voltage Level Definitions VIL – Low Level Input Voltage Vinput ≤ VIL to be recognized as a “0” TTL Ex: ECE 3450 VIL = 0.8V, thus at the input a “0” is between 0V and 0.8V M. A. Jupina, VU, 2014 Voltage Level Definitions VOL – Low Level Output Voltage TTL Ex: ECE 3450 VOL = 0.4V, thus at the output a “0” is between 0V and 0.4V M. A. Jupina, VU, 2014 Logic Level Matching Levels at output of one gate must be sufficient to drive next gate. VOH > VIH VOL < VIL ECE 3450 M. A. Jupina, VU, 2014 Voltage Level Definitions VLS – logic swing at the output VLS = VOH - VOL Ideally, should be as large as possible. Higher VLS reduces ambiguity in the output logic state and increases noise immunity. VLS defines the range of output voltages that define the unknown state, “X” state. ECE 3450 M. A. Jupina, VU, 2014 Voltage Level Definitions VTW – transition width at the input VTW = VIH - VIL Ideally, should be as small as possible. Lower VTW reduces ambiguity in the input logic state and increases noise immunity. VTW defines the range of input voltages that define the unknown state, “X” state. ECE 3450 M. A. Jupina, VU, 2014 Voltage Levels Summary “1” “X” “0” ECE 3450 “1” “X” “0” M. A. Jupina, VU, 2014 Noise in Digital Circuits • Noise – unwanted variations of voltages and currents at the logic nodes • from two wires placed side by side – capacitive coupling • voltage change on one wire can influence signal on the neighboring wire • cross talk – inductive coupling • current change on one wire can influence signal on the neighboring wire v(t) i(t) • from noise on the power and ground supply rails – can influence signal levels in the gate ECE 3450 VDD M. A. Jupina, VU, 2014 Noise Margin Definitions NM’s define the amount of noise immunity in the high or low level logic state. NMH - High Level Noise Margin NMH = VOH - VIH NML - Low Level Noise Margin NML = VIL - VOL Ideally, the NM’s should be as large and as equal as possible. NM of a technology = min{NMH , NML} TTL Ex: NMH = 2.4V - 2V = 0.4V NML = 0.8V – 0.4V = 0.4V ECE 3450 M. A. Jupina, VU, 2014 Noise Superimposed on TTL Signals OR ECE 3450 M. A. Jupina, VU, 2014 Noise Margin Question A certain logic family has the following voltage parameters: VIH = 1.18 V, VOH = 4 V, VIL = 0.7 V, VOL = 0.15 V What is the largest positive-going noise spike that can be tolerated? NML = VIL – VOL = 0.55V What is the largest negative-going noise spike that can be tolerated? NMH = VOH – VIH = 2.82V ECE 3450 M. A. Jupina, VU, 2014 PSPICE Noise Simulation Demonstrating the Concept of Noise Margin (LS7404) ECE 3450 M. A. Jupina, VU, 2014 PSPICE Noise Simulation V(IN) = Source + Noise VOH VOL ECE 3450 Vpeak-to-peak M. A. Jupina, VU, 2014 PSPICE Noise Simulation V(OUT) for Vpeak= 0, 0.5, 1, 3.1V Vpeak=0V Vpeak=1V ECE 3450 Vpeak=0.5V Vpeak=3.1V M. A. Jupina, VU, 2014 The Ideal Inverter The ideal gate should have – – – – – infinite slope (gain) in the transition region high and low noise margins equal to half the logic swing a gate threshold located in the middle of the logic swing input and output impedances of infinity and zero, respectively infinite output drive capability (infinite output current or fanout) VOUT VOH = VCC Ideal VTC VCC = VSUPPLY VTW=0 (Impossible to be in X state) NMH = NML = VCC/2 dVo VLS=VCC dVi Ri = Ro = 0 Fanout = VOL = 0V ECE 3450 VIL=VIH= VCC/2 VIN M. A. Jupina, VU, 2014 Current Level Conventions Current out of a terminal is given as a negative value in Data Sheets. Current into a terminal is given as positive value in Data Sheets. ECE 3450 M. A. Jupina, VU, 2014 Table of Current Levels for TTL Families ECE 3450 M. A. Jupina, VU, 2014 Current Sourcing Versus Current Sinking ECE 3450 M. A. Jupina, VU, 2014 Current Level Definitions IOL – Low Level Output Current “0” IOUT Maximum current that an output terminal of a gate can sink when the output is “0”. If |IOUT| > |IOL|, then eventually VOUT > VOL TTL Ex: IOL = +16mA, VOUT ≤ 0.4V ECE 3450 M. A. Jupina, VU, 2014 Current Level Definitions IIL – Low Level Input Current “0” IIN Maximum current that an input terminal of a gate can source when the input is “0”. TTL Ex: IIL = -1.6mA, VIN ≤ 0.8V ECE 3450 M. A. Jupina, VU, 2014 Current Level Definitions IOH – High Level Output Current “1” IOUT Maximum current that an output terminal of a gate can source when the output is “1”. If |IOUT| > |IOH|, then eventually VOUT < VOH TTL Ex: IOH = -400mA, VOUT ≥ 2.4V ECE 3450 M. A. Jupina, VU, 2014 Current Level Definitions IIH – High Level Input Current “1” IIN Maximum current that an input terminal of a gate can sink when the input is “1”. TTL Ex: IIH = +40mA, VIN ≥ 2.0V ECE 3450 M. A. Jupina, VU, 2014 TTL Example – LED Load Which circuit would you use to drive an LED? (Assume that VLED = ~1.7 V.) I + 1.7 V I - + 1.7 V ECE 3450 M. A. Jupina, VU, 2014 TTL Example – LED Load Analysis of the first circuit: I + 1.7 V For this circuit, Vout ≥2.4V and thus I ≥ 2mA > IOH ! (IOH = -0.4mA) This TTL logic device can’t supply this amount of current since the output voltage will decrease as the output current exceeds IOH. Thereby, a “1” state at the output is no longer guaranteed. ECE 3450 M. A. Jupina, VU, 2014 TTL Example – LED Load Analysis of the second circuit: I - + 1.7 V If Vout = 0.4V, then I = 9 mA < IOL. ( IOL = 16 mA ) If Vout = 0V, then I = 10 mA < IOL. The necessary output current can be supplied. For TTL, the magnitude of IOL > the magnitude of IOH ECE 3450 M. A. Jupina, VU, 2014 Fan-Out and Fan-In Fan-out – number of load gates connected to the output of the driving gate gates with large fan-out are slower N Fan-in – the number of inputs to the gate ECE 3450 M gates with large fan-in are bigger and slower M. A. Jupina, VU, 2014 Static or DC Fan-Out Fan-Out (N) is defined as the number of loads (gate inputs) that can be driven by a single gate output at DC or low frequencies. Low Level Fan-out NL = I OL of the driving gate I IL of the load gate NH = I OH of the driving gate I IH of the load gate High Level Fan-out N = min{NL,NH} Ex: For most TTL families, N = NL. ECE 3450 M. A. Jupina, VU, 2014 TTL Static Fan-Out Example NL 16mA 10 1.6mA NH 400m A 10 40m A N 10 ECE 3450 M. A. Jupina, VU, 2014 Dynamic Fan-Out Additional current due to the capacitive load. The impedance of a capacitor, (wC)-1, decreases as the frequency increases. Therefore, the load current increases as the frequency increases. This additional load current must be taken into account when determining fan-out at high frequency. Dynamic Fan-Out << Static Fan-Out ECE 3450 M. A. Jupina, VU, 2014 Power Dissipation Definitions Instantaneous power: p(t) = v(t)i(t) = Vsupplyi(t) Peak power: Ppeak = Vsupplyipeak Average power: Vsupply 1 t T Pav p(t )dt T t T ECE 3450 t T t isupply ( t ) dt M. A. Jupina, VU, 2014 Power Dissipation Power consumption: how much energy is consumed per operation and how much heat the circuit dissipates power supply sizing (determined by peak power) Ppeak = Vsupplyipeak – battery lifetime (determined by average power dissipation) p(t) = v(t)i(t) = Vsupplyi(t) Pavg= 1/T p(t) dt = Vsupply/T isupply(t) dt – packaging and cooling requirements Two important components: static (DC) and dynamic CMOS Example: PAV = VDD Ileakage + CL VDD2 f ECE 3450 M. A. Jupina, VU, 2014 TTL Supply Currents • The power supply current is dependent on the output state. • ICCL > ICCH since IOL > IOH IIL > IIH Note: these values are for a 7400 NAND Gate chip (total current for 4 NAND gates) Power Dissipation of a TTL Gate PAV PCCAV PEEAV PAV I CCH ( gate ) I CCL ( gate ) 2 VCC I EEH ( gate ) I EEL ( gate) 2 VEE For VEE 0 PAV ECE 3450 I CCH ( gate ) I CCL ( gate ) 2 VCC M. A. Jupina, VU, 2014 Power Dissipation of a TTL Gate Example What is the power dissipation of a single TTL NAND gate (7400)? 8mA I CCH ( gate) 2mA 4 22mA I CCL ( gate) 5.5mA 4 2mA 5.5mA PAV (5V ) 18.75mW 2 ECE 3450 M. A. Jupina, VU, 2014 Power Supply Currents Versus Frequency 10 KHz ECE 3450 100 KHz 1 MHz 10 MHz 100 MHz M. A. Jupina, VU, 2014 Propagation Delay Time Vin Vout A measure of how long it takes for a gate to change state. Ideally, should be as short as possible. tPHL - the time it takes the output to go from a high to a low Average Propagation Delay Time tp = ECE 3450 t pHL t pLH 2 tPLH - the time it takes the output to go from a low to a high M. A. Jupina, VU, 2014 Modeling Propagation Delay Model circuit as a first-order RC network R vout C vin I R IC V Vout (t ) dVout (t ) C R dt V Vout (t) = (1 – e–t/)V ,where = RC Time to reach 50% point is t = ln(2) = 0.69 0 t ECE 3450 M. A. Jupina, VU, 2014 Modeling Propagation Delay Driver Gate and Load Gate are modeled as a first-order RC network vout R vin vS C + - Driver ECE 3450 Load M. A. Jupina, VU, 2014 CMOS Inverter as an Example VDD + pullup network in out out in Drain pulldown network VSS ECE 3450 M. A. Jupina, VU, 2014 Switch Models of a CMOS Inverter VDD VDD Rp Vout = 0 Vout = VDD Rn Vin = V DD ECE 3450 Vin = 0 M. A. Jupina, VU, 2014 CMOS Inverter: Transient Response V DD V DD Rp Capacitor Charging Capacitor Discharging V out V out CL CL Rn V in 0 (a) Low-to-high output ECE 3450 V in V DD (b) High-to-low output M. A. Jupina, VU, 2014 CMOS Inverter Propagation Delay • Propagation delay is proportional to the time-constant of the network formed by the pull-down resistor or pull-up resistor and the load capacitance. tpHL = ln(2) Rn CL = 0.69 Rn CL tpLH = ln(2) Rp CL = 0.69 Rp CL tp = (tpHL + tpLH)/2 = 0.69 CL(Rn + Rp)/2 • To equalize propagation delay times make the onresistance of the NMOS and PMOS approximately equal. ECE 3450 M. A. Jupina, VU, 2014 PSPICE Simulation of Delay with RC Models (Switch) ECE 3450 M. A. Jupina, VU, 2014 The Effect of Fan-Out on Propagation Delay x f V out To inputs of x n other inverters To inputs of n other inverters Cn (a) Inverter that drives n other inverters (b) Equivalent circuit for timing purposes V out for n =1 VDD V out for n = 4 Gnd 0 Time (c) Propagation times for different values of n ECE 3450 M. A. Jupina, VU, 2014 Measurement of the Average Propagation Delay Time under Loaded Conditions Ring Oscillator Circuit T = Period 10 10 01 N = odd number of gates, tp = T/2N Typically, CL= 15pf or 50pF Note: This is a self-oscillating circuit that requires no signal input. ECE 3450 M. A. Jupina, VU, 2014 Maximum Frequency of Operation FMAX 1 2 max(tPLH , tPHL ) TTL Ex: tPLH = 22ns, tPHL = 15ns Fmax = 22 MHz ECE 3450 M. A. Jupina, VU, 2014 Propagation Delay and Power Dissipation (for a single gate) TTL { CMOS { TTL Comparison ECE 3450 M. A. Jupina, VU, 2014 Propagation Delay Versus Power Dissipation (for a single gate) Ideal ECE 3450 M. A. Jupina, VU, 2014 Power Dissipation and Propagation Delay • Propagation delay and the power consumption of a gate are related • Propagation delay is (mostly) determined by the speed at which a given amount of energy can be stored on the gate – the faster the energy transfer (higher power dissipation) the faster the gate • For a given technology, the product of the power consumption and the propagation delay is a constant and is used as a benchmark to compare digital technologies. – Power-Delay Product (PDP) specifies the energy consumed by the gate per switching event • An ideal gate is one that is fast and consumes little energy and therefore the PDP should be as small as possible. ECE 3450 M. A. Jupina, VU, 2014 Power-Delay Product Calculation The average power dissipation (mW) by a single gate is multiplied by the average propagation delay time (ns) of a single gate to get the total energy (pJ) dissipated by a gate for a given technology. Compare the PDP of 4000 CMOS, ALS TTL, and ECL CMOS: PDP = (1mW) (100ns) = 100pJ ALS TTL: PDP = (1.5mW)( 4ns) = 6pJ ECL: PDP = (40mW) ( 1ns) = 40pJ ECE 3450 M. A. Jupina, VU, 2014 Common IC Packages ECE 3450 M. A. Jupina, VU, 2014 Comparison of Microprocessors in 2001 ECE 3450 M. A. Jupina, VU, 2014 How much space does a single MOS transistor occupy on a silicon chip? Example: 100 million transistors on a 1cm x 1cm Si die. 108 transistors N N 1 transistor 1 transistor or 2 2 -8 2 1cm 1cm 10 cm 1m m2 OR 1 cm N N 1 cm 104 transistors N cm Source or 1 transistor 1 transistor -4 10 cm 1m m L<0.1 mm Gate Drain ~1 mm ~1 mm ECE 3450 M. A. Jupina, VU, 2014 Moore’s Law in Microprocessors Transistors on lead microprocessors double every 2 years 1000 2X growth in 1.96 years! Transistors (MT) 100 Pentium® IV 10 486 1 386 286 0.1 0.01 8086 8080 8008 4004 8085 0.001 1970 ECE 3450 Pentium® proc 1980 1990 Year Courtesy, Intel 2000 2010 M. A. Jupina, VU, 2014 Intel 4004 Microprocessor 1971 2300 transistors 1 MHz clock ECE 3450 M. A. Jupina, VU, 2014 Intel Pentium (IV) Microprocessor 2001 42 million transistors 2 GHz clock ECE 3450 M. A. Jupina, VU, 2014 Evolution in DRAM Chip Capacity human memory human DNA 100000000 10000000 64,000,000 4X growth every 3 years! 16,000,000 Kbit capacity/chip 4,000,000 1000000 1,000,000 book 100000 256,000 64,000 16,000 10000 4,000 1000 1,000 256 100 64 10 1980 0.07 mm 0.1 mm 0.13 mm 0.18-0.25 mm 0.35-0.4 mm 0.5-0.6 mm 0.7-0.8 mm 1.0-1.2 mm encyclopedia 2 hrs CD audio 30 sec HDTV 1.6-2.4 mm page 1983 1986 1989 1992 1995 Year 1998 2001 2004 2007 2010 Clock Frequency Lead microprocessors frequency doubles every 2 years 10000 2X every 2 years Frequency (Mhz) 1000 100 Pentium® proc 486 10 8085 1 0.1 1970 ECE 3450 Pentium® IV 8086 286 386 8080 8008 4004 1980 1990 Year Courtesy, Intel 2000 2010 M. A. Jupina, VU, 2014 Power Dissipation Lead Microprocessors power continues to increase 100 Pentium® IV Power (Watts) Pentium® proc 10 8086 286 1 8008 4004 486 386 8085 8080 0.1 1971 1974 1978 1985 1992 2000 Year Power delivery and dissipation will be prohibitive ECE 3450 Courtesy, Intel M. A. Jupina, VU, 2014 Power Density Power Density (W/cm2) 10000 Rocket Nozzle 1000 Nuclear Reactor 100 8086 Pentium® IV 10 4004 Hot Plate 8008 8085 Pentium® proc 386 286 486 8080 1 1970 1980 1990 Year 2000 2010 Power density too high to keep junctions at low temp ECE 3450 Courtesy, Intel M. A. Jupina, VU, 2014 Power Dissipation (Battery Lifetime) is an issue in all types of handhelds ECE 3450 M. A. Jupina, VU, 2014 What is the Current Power Dissipation in Processors? • For a group exercise in class, select a processor manufactured during the last three years and provide information on its power dissipation by specifying the thermal design power (TDP). • TDP is the maximum amount of heat generated by the processor which the cooling system is required to dissipate. • Look at processors manufactured by Intel, AMD, or Freescale and use the manufacturers’ web sites to obtain the information. Provide the website where you found your information. Specify the properties of the processors such as clock frequency, die size, number of transistors, and the number of cores (if applicable). • Use the excel spreadsheet form at the course website to report your findings and email this file to your instructor when completed. ECE 3450 M. A. Jupina, VU, 2014