Comparison MM74HC 74LS, 74ALS Logic MM54HC/MM74HC family high spe
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Comparison MM74HC 74LS, 74ALS Logic
Comparison MM74HC 74LS, 74ALS Logic
MM54HC/MM74HC family high speed logic components provides combination speed power characteristics that duplicated bipolar logic families other CMOS family. This CMOS family operating speeds similar power Schottky (54LS/74LS) technology. MM54HC/MM74HC approximately half fast (delays twice long) 54ALS/74ALS 54S/74S logic. Compared CD4000 54C/74C, this order magnitude improvement speed, which achieved utilizing advanced micron silicon gate-recessed oxide CMOS process. MM54HC/MM74HC components designed retain advantages older metal gate CMOS, plus provide speeds required today's high speed systems. Another advantage MM54HC/MM74HC family that provides functions outs popular 54LS/74LS series logic components. Many functions which unique CD4000 metal gate CMOS family have also been implemented this high speed technology. addition, MM54HC/MM74HC family contains several special functions previously implemented CD4000 54LS/74LS. Although functions speeds same 54LS/74LS, some electrical characteristics different from either LS-TTL, S-TTL ALS-TTL. following discusses these differences highlights advantages disadvantages high speed CMOS.
Fairchild Semiconductor Application Note June 1983
PERFORMANCE mentioned previously, MM54HC/MM74HC logic family been designed have speeds equivalent LS-TTL, 8-10 times faster than CD4000B MM54C/ MM74C logic. Table compares high speed CMOS bipolar logic families. HC-CMOS gate delays typically same LS-TTL, ALS-TTL three times faster. S-TTL also about twice fast HC-CMOS. Flip-flop counter speeds also follow same pattern.
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FIGURE ALS, Comparison Propagation Delay Load NAND Gate
TABLE Comparison Typical Performance LS-TTL, S-TTL, ALS-TTL HC-CMOS Gates 74XX00 74XX04 74XX139 Propagation Delay Propagation Delay Propagation Delay Select Enable 74XX151 Propagation Delay Address Strobe 74XX240 Clocked 74XX174 74XX374 Propagation Delay Operating Frequency Propagation Delay Enable/Disable Time Operating Frequency Propagation Delay Enable/Disable Time LS-TTL ALS-TTL HC-CMOS S-TTL Units
Combinational
Also, logic's propagation delay variation changes capacitive loading very similar LS-TTL. Figure illustrates this plotting delay versus loading various bipolar logic families MM54HC/MM74HC. HC-CMOS virtually same speed load-delay variation LS-TTL and, expected, slower than S-TTL logic.
slopes these lines indicate amount variation speed with loading, dependent output impedance particular logic gate. delay variation LS-TTL HC-CMOS similar whereas ALS-TTL S-TTL have slightly less variation.
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1998 Fairchild Semiconductor Corporation
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POWER DISSIPATION CD4000B MM54C/MM74C CMOS devices well known extremely quiescent power dissipation, high speed CMOS retains this feature. Table compares typical static power consumption with S-TTL. Even CMOS dissipation well below while LS-TTL dissipation many milliwatts. This makes MM54HC/MM74HC ideal battery operated ultra-low power systems where system "sleep" shutting system clock. TABLE Comparison Typical Quiescent Supply Current Various Logic Families HC-CMOS Flip-Flop 0.0025 0.005 0.25 LS-TTL 20.0 ALS-TTL S-TTL
croprocessor based system. assuming typical load capacitance power dissipation these devices calculated various average system clock frequencies. Figure plots power consumption 74HC, 74LS, 74ALS logic implementations. Above MHz, capacitive currents also tend dominate bipolar power dissipation well. TABLE Hypothetical "Glue" Logic Typical Microprocessor System System Components Address Decoders ('138) Address Comparators ('688) Address/Data Buffers ('240/4) Address/Data Latches ('373/4) Control/Gating ('00, '10) Misc. Counter/Shift ('161, '164) Flip-Flops ('73/4)
CMOS dissipation increases proportionately with operating frequency. Doubling operating frequency doubles current consumption. This currents generated charging internal load capacitances. Figure shows power dissipation versus frequency completely unloaded NAND gate, flip-flop counter implemented technologies. curves essentially flat because quiescent currents mask capacitive effects, except very high frequencies. Capacitive effects slightly lower families, that, high frequencies, CMOS dissipation actually more than However, power crossover frequency usually well above maximum operating frequency MM54HC/MM74HC. previously mentioned curves plot unloaded circuits. When considering typical system power consumption, capacitive loading should also considered. Table lists components implement support logic small
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FIGURE Power Consumption Hypothetical Microprocessor System Support Logic
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FIGURE Supply Current Consumption Comparison 74XX00 74XX714 74XX161 Circuits Since, typical system, some sections will operate high frequency other parts lower frequencies, average system clock frequency simplification. example, microprocessor will have cycle frequency MHz. Most system memory components will accessed small amount time, resulting effective clock frequencies order these sections. Thus, average system clock frequency would around MHz, power savings would realized using CMOS. Another simplification made calculate system power. CMOS circuits will dissipate much less power when 3-STATE, which would save much power since, given
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cycle, only buffers will enabled. however, actually dissipate more power when their outputs disabled. Several interesting conclusions drawn from Figure First, notice that, higher frequencies, bipolar logic families start dissipate more power. This result current consumption switching load. operating frequency approaches infinity, this will dominant effect. extremely fast power systems, minimizing load capacitance overall operating frequency becomes more important. lower power logic introduced, system power will increasingly dependent capacitive load effects similar CMOS. Second, logic slightly smaller logic voltage swing than CMOS. Thus, given load, will actually have lower average load current. similar unloaded example, very high frequencies, CMOS could consume more power than TTL. Figure indicates, these frequencies usually above limit HC-CMOS LS-TTL.
INPUT VOLTAGE CHARACTERISTICS NOISE IMMUNITY maintain advantage CMOS noise immunity, input logic levels defined similar metal gate CMOS. MM54HC/MM74HC designed have input voltages 3.5V 1.0V. Additionally, input voltage over operating supply voltage range 0.7VCC 0.2VCC. This compares 2.0V 0.8V specified LS-TTL over supply range. Figure illustrates input voltage differences, greater noise immunity logic over supply range. Maintaining wide noise immunity gives HC-CMOS advantage many industrial, automotive, computer applications where high noise levels exist.
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FIGURE Worst-Case Input Output Voltages Over Operating Supply Range Logic
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FIGURE Input-Output Transfer Characteristics 74XX00 NAND Gate Implemented HC-CMOS LS-TTL ALS-TTL
Another indication noise immunity typical transfer characteristics logic families. Figure shows transfer function 74XX00 NAND gate HC-CMOS, LS-TTL ALS-TTL. High speed CMOS very sharp transition typically 2.25V, this transition point very stable over temperature. bipolar logic transfer functions sharp vary several hundred millivolts over temperature. This sharp transition large circuit gains provided triple buffering HC-CMOS gate com3
pared single bipolar gain stage. Figure compares transfer function 'HC08 'ALS08, both which double buffered. 'ALS08 sharper transition, CMOS gate still less temperature variation more centered trip point. However, trip point dependent variation CMOS high speed CMOS input levels totally compatible with output voltage specifications. make them com-
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patible would compromise noise immunity, size, significant speed. designer improve compatibility adding pull-up resistor output. also utilize series TTL-to-CMOS level converters which being provided ease design mixed HC/LS/ALS/S systems. These buffers have 0.8V 2.0V input voltage specifications, provide CMOS compatible outputs. When mixing logic, noise immunity CMOS interface better than LS-TTL, substantial savings power will occur when using MM54HC/MM74HC logic. INPUT CURRENT family maintains ultra-low input currents typical CMOS circuits. This current less than caused input protection diode leakages. This compares
much larger LS-TTL input currents input high input. ALS-TTL input currents S-TTL input currents Figure tabulates these values. near zero input current CMOS eases designing, since typical input viewed open circuit. This eliminates need fanout restrictions which necessary logic designs.
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FIGURE Input-Output Transfer Characteristics 74XX08 Gate Implemented HC-CMOS ALS-TTL
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FIGURE Comparison Input Current Specifications Various Logic Families POWER SUPPLY RANGE Figure also compares supply range MM54HC/ MM74HC logic LS-TTL. high speed CMOS family specified operate voltages from 54LS, 54ALS logic specified operate from 4.5V 5.5V, 74LS will operate from 4.75V 5.25V. 74ALS specified over 4.5V 5.5V supply range. This wider operating range family eases power supply design eliminating costly regulators enhances battery operation capabilities.
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OUTPUT DRIVE Since there speed, noise immunity, power trade-off, standard HC-CMOS designed have similar high current output drive that characteristic LS-TTL ALS-TTL. Schottky about times output drive MM54HC/MM74HC. Thus HC-CMOS output current specification output voltage 0.4V. keeping with CD4000B series 54C/74C series logic, source sink currents symmetrical. Thus logic source well. This large increase output current high speed CMOS over CD4000B also added advantage reducing signal line crosstalk which greater concern high speed systems. Figure compares specified output currents. Since logic families have significant input currents they have limited fanout capability. Table illustrates limitations these families, based their input output currents. High speed CMOS also included. MM54HC/ MM74HC same CMOS-to-CMOS fanout characteristics CD4000B, virtually infinite.
TABLE Fanout HC-CMOS, LS-TTL, ALS-TTL, S-TTL From, 74HC 74LS 74ALS 74HC 4000
74LS
74ALS
another indication similarity HC-CMOS LS-TTL, Figure plots typical output currents versus output voltage output sink current curves very similar, source current somewhat different, emitter-follower output circuitry. MM54HC/MM74HC driving circuits, namely 3-STATE buffers latches, have half again much output current drive standard outputs. These components have output drive. chosen based trade-off size speed-load variations. This current less than more specified driver circuits, because fanout limitations these families apply CMOS systems. S-TTL output sink current
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FIGURE Output Current Specifications ALS-TTL, S-TTL HC-CMOS
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FIGURE Comparison Standard LS-TTL HC-CMOS Output Source Sink Currents
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OPERATING TEMPERATURE RANGE operating temperature range temperature effects various HC-CMOS operating parameters differ from bipolar logic. recommended temperature range 74LS, 74S, 74ALS 70°C, compared -40°C 85°C 74HC family. series logic specified from -55°C 125°C four families. Temperature variation operating parameters MM54HC/MM74HC family behaves very predictably gain decreasing MOSFET transistors temperature increased. Thus output currents decrease propagation delays increase about 0.3% degree centigrade.
Note, though, that outputs completely compatible with various family's input specifications; therefore, there problem when driving TTL. Another source possible problems occur when design floats device inputs. This practice recommended when using LS-TTL, sometimes done. Usually, inputs float high; however, CMOS inputs float either high depending static charge input. therefore important always unused CMOS inputs either ground avoid incorrect logic functioning. third factor consider when replacing logic performance. logic functions provided 54HC/74HC equivalent LS-TTL, propagation delay, set-up hold times similar However, there some differences CMOS circuits implemented which will cause differences speed. most part, these differences minor, important verify that they affect design. CONCLUSION MM54HC/MM74HC family represents major step forward CMOS performance. full line family capable being designed into virtually application which uses LS-TTL with substantial improvement power consumption. S-TTL primarily offer faster speeds than HC-CMOS, still have input output advantages lower power consumption CMOS. Because high input impedance large output drive, logic actually easier use. This, coupled with continued expansion 54HC/74HC, will make increasingly popular logic family.
Figure shows typical propagation delays 74XX00 over -55°C +125°C temperature range. 'HC00's speed increases almost linearly with temperature, whereas behave differently.
WORD ABOUT PLUG-IN REPLACEMENT MM54HC/MM74HC logic implements equivalent functions with same outs TTL. designed directly plug-in replaceable, but, with some care, some systems converted MM54HC/MM74HC with little modification. replaceability determined several factors. factor difference input levels. systems where being replaced outputs feed CMOS inputs, input high voltages, specified, totally compatible. Although outputs will typically drive inputs correctly, external pull-up resistor should added outputs, MM54HCT/MM74HCT compatible circuit should used. This incompatibility tends limit designer's ability intermingle HC-CMOS.
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FIGURE Propagation Delay Variation Across Temperature 74LS00 74ALS00 74HC00
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Comparison MM74HC 74LS, 74ALS Logic
LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT FAIRCHILD SEMICONDUCTOR CORPORATION. used herein: critical component component life support Life support devices systems devices sysdevice system whose failure perform reatems which, intended surgical implant into sonably expected cause failure life support body, support sustain life, whose device system, affect safety effectiveness. failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user.
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Fairchild does assume responsibility circuitry described, circuit patent licenses implied Fairchild reserves right time without notice change said circuitry specifications.
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