# RF Amplifier

### What is an Amplifier?

An Amplifier is an electronic device that amplifies a time-dependent voltage or a current signal.

In simple words, an Amplifier is an electronic device that increases the power of an input voltage signal or input current signal.

At the output, we may find an amplified signal.

## What is radiofrequency?

Radio Frequency is a spectrum of frequencies that represent electromagnetic waves ranging from 30kHz to 300 GHz.

The radiofrequency spectrum consists of frequency bands ranging from very low frequencies to very high frequencies.

## Why do we use radio frequencies?

When we need wireless communication, we require RF waves.

On the sender side, we have an antenna that transforms an electrical signal into an electromagnetic wave. This wave has a frequency that belongs to the radio spectrum. They travel towards the receiver which may be distances apart. The receiver converts the electromagnetic waves into an electrical signal. This is how wireless communication is possible.

Applications of RF are wireless including TVs, wireless LANs, radios, etc.

## What is a Radio Frequency Amplifier?

An amplifier that amplifies or increases the power of an input radio frequency signal is known as an RF amplifier.

These RF amplifiers are generally the amplifiers that increase the power of a low-energy signal or message signal at the input side and transfer it to the antenna for further communication. They are used on the input side while RF attenuators are used on the output side.

Where,

Vin = Input Voltage

Vout = Output Voltage

Pi = Input Power

Po = Output Power

Av = Voltage Gain

Ap = Power Gain

Ac = Current Gain

Ci = Input decoupling capacitor

Co = Output decoupling capacitor

### Small signal gain and Large signal gain

Whenever a signal Vin is applied as an input to the RF amplifier, the signal possesses power as Pi

Pi= Vi x Ii

Then, output power increases with the applied input power and there is not much difference between input power and output power. The relationship is linear.

Pout= Vout x Io

So, the gain of the amplifier obtained is small.

This is known as small-signal gain because

Ap= Pout/Pin, Pout ≅ Pin

Ap≅1.

The value obtained is small. Close to 1.

But beyond a saturation point, The output power doesn’t increase with input power but decreases beyond that point. This makes the gain of the amplifier decrease and operates in the non-linear region.

As, Ap= Pout/Pin, Pout<Pin

Ap<1.

This is known as large signal gain.

Pout= Vout x Iout

### Linear Power and Saturated Power:

Whenever an Amplifier operates, it operates in two regions-Linear and Non-Linear

When the input power is proportional to output power, this relationship is linear. This is known as linear power.

When the amplifier reaches its saturation point, a point beyond which no increase in input power will make a linear relationship with the output power, the amplifier enters the saturation region.

This is known as saturation power. In the Saturation region, input and output power has a non-linear relationship.

#### P1dB:

The output power level at which the amplifier’s gain drops 1 dB from its constant value is known as P1dB. An amplifier enters compression once it hits its P1dB.

• This produces noise.
• This factor isn’t desirable.

### Cin and Cout

These are decoupling capacitors, purpose of the capacitors is to pass AC signal and stop any kind of DC signal mixed within the input and output sides of the amplifiers.

### Impedance matching network

These networks are there on the input side and output side of the amplifier.

They are there to minimize any kind of reflection or scattering.

Usually, impedance is 50 Ohms for matching.

Z0=ZL=50 Ohms.

Values of RFC and decoupling capacitors are calculated by smith charts.