One of the most important choices an RF engineer will make is deciding what kind of output signal is the best fit for the project they’re working on.
There are many benefits to complementary metal-oxide-semiconductor (CMOS) outputs, but there are different variations on this technology. Some types are more appropriate for certain applications than others.
In this blog, we’ll discuss the benefits of low-voltage CMOS (LVCMOS) outputs and how they differ from standard CMOS.
CMOS & LVCMOS Explained
There are a number of advantages that CMOS has over other types of output signals. CMOS clocks are generally inexpensive, keep phase noise to a minimum, and are well-suited to digital circuit designs, particularly those with shorter trace lengths. A compelling argument could be made, however, that the greatest advantage of CMOS technology is its lower power requirements compared to other types of outputs.
CMOS integrated circuits were first developed in the 1960s. One of their distinguishing features was their ability to operate over a wider range of power supply voltages than other circuit types — anywhere from 3 to 15 volts.
As time passed and the technology continued to improve, there was a shift towards lower supply voltage in CMOS designs. Manufacturers began to reduce the geometry of their circuit designs in order to cut costs and improve performance.
This reduction in size was necessarily accompanied by a further reduction in the use of power, so the resistors could operate as intended. As a result of this scaling down of CMOS technology, a new “low voltage” class of CMOS integrated circuits (LVCMOS) was born.
Related: The Beginner's Guide to Understanding CMOS Clocks
LVCMOS Voltage Levels
What constitutes low voltage? The Joint Electron Device Engineering Council (JEDEC) has defined the supply voltage and interface standards for LVCMOS:
- 3.0 V – 3.3 V
- 2.5 V ± 0.2 V (Normal Range) and 1.8 V – 2.7 V (Wide Range)
- 1.5 V ± 0.1 V (Normal Range) and 0.9 V – 1.6 V (Wide Range)
- 1.2 V ± 0.1 V (Normal Range) and 0.8 V – 1.3 V (Wide Range)
- 1.0 ± 0.1 V (Normal Range and 0.7 V – 1.1 V (Wide Range)
Is a LVCMOS Output Signal Right for My Application?
LVCMOS output signals are used for certain low-powered medical imaging equipment, as well as for portable testing and measurement devices, industrial testing equipment, and networking and communication systems. LVCMOS is well suited to both wireless and wired infrastructures.
So, is it the best output for your application?
The short answer is: it depends. Specifically, it all depends on what your power availability is for your application. If you have access to more power and the application requires it, then going with a higher voltage CMOS clock might make more sense. If your power supply is limited and you are trying to reduce power costs, then LVCMOS is the way to go.
Related: CMOS Clocks: Common & Advanced Applications
Make Informed Decisions with Bliley
CMOS and its variants have a lot of advantages. But when you're deciding which signal output to go with, it’s important to get it right the first time during the design stage. Your decision will also depend on what your priorities are, such as reducing phase noise or power usage. It can be a tough choice, and making the wrong one can result in a lot of wasted time and money.
To help make the decision process easier for you, we’ve put together a helpful guide that analyzes the pros and cons of all single-ended and differential output types.
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