Terminology » Components » CMOS vs HCMOS vs LVCMOS: Key Differences Explained

CMOS vs HCMOS vs LVCMOS: Key Differences Explained

cmos hcmos lvcmos logic family voltage level

This article compares CMOS, HCMOS, and LVCMOS, highlighting their differences in voltage levels, advantages, and disadvantages.

Introduction: CMOS Technology

CMOS (Complementary Metal Oxide Semiconductor) circuits utilize both p-channel and n-channel FET (Field-Effect Transistor) devices. These are fabricated on the same substrate to create logic functions. CMOS technology primarily employs NAND and NOR gates as its fundamental building blocks.

CMOS | Complementary Metal Oxide Semiconductor

Here are the typical characteristics of the CMOS logic family:

  • Basic gate used: NAND/NOR
  • Fanout: >50
  • Power per gate: 1 mW @ 1MHz
  • Noise immunity: Excellent
  • Noise margin: 0.3Vcc
  • t PD (Propagation Delay): 1-200 ns
  • 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 a voltage between 0V to 1V
  • Binary Logic “1”: Represented by a voltage between 3.5V to 5V

Advantages of CMOS:

  • Low power dissipation
  • Excellent noise immunity
  • Higher packing density
  • Higher speed
  • Highest fanout
  • Wide supply voltage range

Disadvantages of CMOS:

  • Average propagation delay is worse than TTL (Transistor-Transistor Logic) and ECL (Emitter-Coupled Logic) families.

TTL and CMOS interfacing

Figure: Interfacing between CMOS and TTL.

HCMOS | High Speed CMOS

  • HCMOS stands for High-Speed CMOS.
  • It’s a higher-speed variant of the original CMOS.
  • The specifications of HCMOS are defined by JEDEC (Joint Electron Device Engineering Council).
  • Example: Philips semiconductor device 74HC/HCT/HCU

Advantages of HCMOS:

  • Philips HCMOS devices offer low power in addition to the high speed and drive capability of LSTTL (Low Power Schottky TTL).

CMOS vs LVCMOS

Figure: CMOS and LVCMOS voltage levels

LVCMOS | Low Voltage CMOS

  • LVCMOS stands for Low Voltage CMOS.
  • It’s defined by JEDEC.
  • It represents a low-voltage class of CMOS.
  • The figure above illustrates the voltage levels used by LVCMOS and CMOS logic families.

Applications of LVCMOS:

  • LVCMOS output signals are suitable for low-powered imaging equipment, networking, communication, portable test and measurement equipment, industrial test equipment, etc.

Advantages of CMOS, HCMOS, and LVCMOS:

  • All variants (TTL, CMOS, HCMOS, and LVCMOS) have a single-ended output in the range of 0.5 to 4.5V.
  • The outputs have a square wave digital shape, which is suitable for lower frequency clocking below 250 MHz.
  • They allow direct connection between the clock output and the input of the chip.
  • They are used for high speed and low voltage requirements.

Disadvantages of CMOS, HCMOS, and LVCMOS:

  • In some applications, a series resistor (of low value) is used to reduce signal feedback in order to maintain signal integrity.