CMOS vs HCMOS vs LVCMOS | Difference between CMOS HCMOS LVCMOS
This page compares CMOS vs HCMOS vs LVCMOS and mentions difference between CMOS, HCMOS and LVCMOS with respect to voltage levels, advantages and disadvantages.
Introduction: CMOS circuits use both p-channel and n-channel FET devices. These are fabricated on same substrate to form logic functions. It uses NAND and NOR gates as basic gates.
CMOS | Complementary Metal Oxide Semiconductor
Following are the typical characteristics of CMOS logic family.
• Basic gate used : NAND/NOR
• Fanout : >50
• Power per gate (mWatt) : 1 @ 1MHz
• Noise immunity : Excellent
• Noise margin : 0.3Vcc
• tPD (ns) : 1-200
• Output drive current : Symmetric : Typ. 4mA but AC family can drive 24 mA
In CMOS binary one and zero are represented as follows.
Binary Logic "0" : Represented by voltage between 0V to 1V
Binary Logic "1" : Represented by voltage between 3.5V to 5V
Advantages : Low power dissipation, excellent noise immunity, higher packing density, higher speed, highest fanout,
wide supply voltage range
Disadvantages : Average propagation delay is worst than TTL and ECL families.
The figure depicts interfacing between CMOS and TTL.
HCMOS | High Speed CMOS
• HCMOS stands for High speed CMOS.
• It is higher speed variant of original CMOS.
• The specifications of HCMOS are defined by JEDEC.
• Example : Philips semiconductor device 74HC/HCT/HCU
Advantages: Philips HCMOS device offers low power in addition to high speed and drive capability of LSTTL (Low Power Schottky TTL).
CMOS and LVCMOS voltage levels
LVCMOS | Low Voltage CMOS
• LVCMOS stands for Low Voltage CMOS.
• It is defined by JEDEC.
• It is low voltage class of CMOS.
• Figure depicts voltage levels used by LVCMOS and CMOS logic families.
Applications : LVCMOS output signals are suitable to be used for low powered imaging equipment, networking, communication, portable test and measurement equipments, industrial test requipments etc.
Advantages of CMOS, HCMOS and LVCMOS :
All the variants TTL, CMOS, HCMOS and LVCMOS have single ended output in the range from 0.5 to 4.5V. The outputs have square wave digital shape which is suitable for lower frequency clocking below 250 MHz. It allows direct connection between clock output and input of the chip. They are used for high speed and low voltage requirements.
Disadvantages of CMOS, HCMOS and LVCMOS :
In some applications, series resistor (of low value) is used to reduce signal feedback in order to maintain signal integrity.
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