What Is An Rf Synthesizer

By Author: howard malone
Total Articles: 16

An RF synthesizer is a system or device used to synthesize a predetermined

frequency within a array of frequencies. The

frequencies may be generated from an oscillator or a fixed

timebase. These systems are utilized in a variety of devices, such as mobile phones, GPS systems, radio receivers, CB radios, satellite receivers and

more. To

create the desired output signal, a frequency synthesizer has the ability to combine frequency division with frequency multiplication, and to mix different frequencies.

Televisions once made use of local oscillators

for tuning long before the ability to use synthesizers came about. A major

disadvantage to these oscillators was that the frequency would change

slightly due to temperature variations and aging equipment. This was not reliable enough, so more preciseness was necessary.

Numerous RF synthesizer techniques have been created throughout the

past decades. Some of these provided better proficiency than some other synthesizers did. Some

methods used quartz crystals, which grew to be costly in

applications where many frequencies were needed. For instance, FM radio can

support 100 different frequencies, and crystals were needed for each

frequency. When it comes to cable television, a larger number of frequencies is feasible, which means even

more crystals are needed. Quartz crystals are very

efficient; however they are simply not cost effective.

Methods of employing synthesizers

can include phase locked loops (PLL's), direct digital synthesis, double

mix, triple mix, and double mix divide. The technique that is used is determined

by expense, the degree of difficulty, frequency step durations and other criteria. The term "coherent" describes the process of frequency generation that comes from one oscillator that doesn't change.

Crystal oscillators are frequently used for oscillators in coherent systems,

although other effective mediums can be utilized.

Incoherent methods make frequencies from a few stable

oscillators. Commercial applications generally employ coherent methods

as a result of the low cost and simplicity of these systems.

Commercial radio receivers often use RF synthesizers based on PLL's. PLL can be described as system of

feedback control.

It creates an error signal as a result of two input

phases. The

error signal can be used to operate an oscillator that is voltage-

controlled. This generates an output frequency, which is sent through a frequency divider and back into the system's input. A negative feedback

loop is created because of this. In the

event of a change in the output frequency, there will be a boost in the

error signal which permits for auto correction to some extent. The alternative input will become the reference input and is the frequency at

which the system becomes locked into place. A

crystal oscillator typically generates the reference frequency

because of the fact that the crystal oscillators have a consistent frequency.

With a

frequency synthesizer, you can accomplish nearly any frequency you would

like by multiplying the reference frequency by a predetermined amount. The applications of these synthesizers are vast, and seem to

touch several aspects of everyone's lives. This type of technology is essential for

helping to bring about the ability to use cell phones, TVs, radios and a variety of other applications that

are made use of on an every day basis. These things are such an

important and mandatory part of life that it would be

difficult to believe the world at large would want to lose the use of these things.
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