Parametric Amplifiers ( Term Paper )

Assalam u alaikum !

Today I want to share a term paper I wrote for my final year Microwave Communication Subject ..

I hope it will be easy to understand the Parametric Amplifiers.

ABSTRACT

This article is a brief study of Parametric Amplifiers. It discusses the needs of communication over long distances and the biggest problem of weak signal transmission and its amplification. Its development is overviewed and structural analysis is also provided to enable reader to understand the componential and logical requirements. This article also covers its working step by step and functionality in different required conditions. Its implementation in different fields and areas is outlined so that the reader would know and understand its applications in real world. In the end current and future research is outlined in the article for the reader to enhance and expand the new ideas. In conclusion, this article lets you through its past, development, structure working and future research areas

It has always been a dire need of humans to communicate over long distances for which they have designed many structures and systems. Long distance communication needs the signal to be either very strong, powerful or to be repeated every time they loses their power. For this problem the need of amplification is raised and solutions have to be found for successfully delivering the signal to desired destination.

In the past there had been many amplification techniques such as operational amplifiers and transistors etc. When it comes to communication we need to be as fast as we can. Old amplifiers were unable to deliver completely at very high frequencies due to their structural and logical limits. For the need of high frequency transmission, scientists invented such amplifiers, which were able to fulfill the required needs. Those amplifiers were named as Parametric Amplifiers and are still currently in use.

As the name suggests, parametric amplifiers use the parameters involved in its structure to provide desired amplification. Parametric Amplifier are constructed as shown in fig 1.

It has a very simple structure consisting of two tank circuits one for signal entrance and output each. PUMP here is the basic component which provides amplification by varying itself. As in the figure it maybe a variable capacitor or varactor diode or any other mechanical machinery that could change the capacitance. Signal is fed in the left tank which has a certain frequency (f1) and a load is connected to tank 2 which varies the frequency of tank 2 (f2). Now the Pump is varied accordingly with these two frequencies to provide amplification and its frequency must satisfy the relation.

            f₃ = f₁ + f₂

Where, f₃ being the frequency of the pump. What happens is when the signal with a certain voltage comes through tank 1 and goes through the PUMP, at that instant when the peak of the signal arrives, pump changes its capacitance which enhances its voltage by following relation.

Q = C _* V

The enhanced voltage is definitely more powerful and is able to travel longer distances.

The main advantages of parametric amplifiers over other amplifiers are their high power handling and very less noise and attenuation. Parametric amplifiers are theoretically lossless due to usage of capacitors and inductors and negative resistance.  Transistors and op-amps on the other hand are not efficient to operate on high powers and high frequencies although with the invention of MESFET and HEMT based devices have overcome these problems and have got an upper hand on parametric amplifiers these days.

Parametric amplifiers are used in various applications such as radio astronomy and long range satellite communications. It can be used in frequency conversions from audio to radio frequencies and can also be employed on high frequency channels such as fiber optics. As everything has some Pros and Cons, parametric amplifiers suffer with the problem of tuning. As they work on LC tank oscillators they work on a very narrow bandwidth and signal can be deviated by external noise and other factors. Parametric amplifiers are used with external filtering circuits to overcome this problem.

Parametric amplifier is currently and for future, a very hot topic of research. Currently with the invention of fiber optics parametric oscillators are being employed in optics as well. Optical parametric amplifier is the latest form of such technology, in which a beam of light of frequency ω_s is split into two different beams of lower frequencies ω₁ and ω₂ by using nonlinear optical crystal with the requirement

ω_s = ω₁ + ω₂.

The output beams in optical parametric generation are usually relatively weak and have relatively spread-out direction and frequency. This problem is solved by using optical parametric amplification (OPA), also called difference frequency generation, as a second stage.

In an OPA, the input is two light beams, of frequency ωs and ω1. The OPA will make the ωs beam weaker, and amplify the ω1 beam, and also create a new beam at the frequency ω2 with ωs=ω1+ω2.

These optical parametric amplifiers are now being used and researched in various fields related to optics. Some of which are:

1-      Spectroscopy

2-      Polarization-independent two-pump fiber OPA.

3-      Continuous-Wave Fiber Optical Parametric Amplifier with 60-dB Gain Using a Novel Two-Segment Design

4-      Quantum metrology with parametric amplifier-based photon correlation interferometers

5-      Frequency domain optical parametric amplification.

Although new technologies have been developed for these requirements, parametric amplifiers still offer a vast area for future research and implementation. With development of optical fiber and other related techniques parametric amplifier is globally being researched by various government and private institutions and organizations and has a greater chance of development in future.

       Citations

Electronic Communication Systems. (1999). 4th ed. MC-Graw-Hill Publications.

1-      Howson, D. and Smith, R. (1970). Parametric amplifiers. 1st ed. London: McGraw-Hill.

2-      Kravtsov, Y. and Osipov, G. (1967). PARAMETRIC AMPLIFIER. 1st ed. Ft. Belvoir: Defense Technical Information Center.

3-      Marhic, M. (2008). Fiber optical parametric amplifiers, oscillators and related devices. 1st ed. Cambridge, UK: Cambridge University Press.

4-      Optical Parametric Amplifier. (2014). [online] Available at: 1- http://en.wikipedia.org/wiki/Optical_parametric_amplifier [Accessed 4 Jun. 2014].

5-      Wikipedia, (2014). Parametric oscillator. [online] Available at: http://en.wikipedia.org/wiki/Parametric_oscillator [Accessed 3 Jun. 2014].

7-  Wikipedia, (2014). Amplifier. [online] Available at: http://en.wikipedia.org/wiki/Amplifier [Accessed 2 Jun. 2014].