High Frequency RF Transistor Amplifier Design

Contents TOC \o "1-3" \h \z \u HIGH FREQUENCY RF TRANSISTOR AMPLIFIER DESIGN PAGEREF _Toc83087187 \h 1INTRODUCTION PAGEREF _Toc83087188 \h 1BASIC THEORY AND CALCULATIONS PAGEREF _Toc83087189 \h 2STABILITY AND IMPEDANCE MATCHING PAGEREF _Toc83087190 \h 5MATLAB CODE PAGEREF _Toc83087191 \h 9References PAGEREF _Toc83087192 \h 10
HIGH FREQUENCY RF TRANSISTOR AMPLIFIER DESIGN
INTRODUCTION
A RF amplifier is an electronic device that converts low power signals to high power signal. Amplifiers are essential parts of any communication system. Any signal needs to be digitalized or amplified to enable long distant transmission from source to receiver.
In the design the design process of any amplifier, a lot of specifications need to be calculated. This specifications include, amplifier gain, amplifier bandwidth, input and output impedance matching and the stability of the amplifier. The stability gain of the transistor has to be also plotted. CITATION AMN08 \l 1033 (Niknejad, 2008)
BASIC THEORY AND CALCULATIONS
The high frequency RF amplifier to be designed is shown below,
In the design process, a linear phase is more preferred because the phase relationship of the input signal is always maintained. For this reason, at all time the frequency components of the signal are delayed by the same amount. As a result, the RF transistor amplifier produces an output that has the same shape as the original input signal. This prevents distortions in signals. CITATION Adv \l 1033 (Advanced solutions, n.d.)
When a non linear phase is used, then the rf amplifier will either amplify or digitalize the input signal but alters the content of the original signal. For this reason, the desired or the expected output will not be achieved. The gain of the amplifier will not be consistent as required.
The key amplifier parameters are as follow,
* Gain and gain flatness (in dB)
* Operating frequency and bandwidth (in dB)
* Output power (in dBm)
* Power supply requirements (in V and A)
* Input and output reflection coefficients (VSWR)
* Noise figure (in dB)
* Intermodular distortion (IMD)
The design specifications are;
Bandwidth of operation is 500 MHz to 1.25GHz
Single pole amplification transistor
Table of s-parameters of the BJT as a function of frequency are shown in the table below;
Frequency

S11

S12

S21

S22

500 MHz

0.70∠-57

0.04∠47

10.5∠136

0.79∠-33

750 MHz

0.56∠-78

0.05∠33

8.6∠122

0.66∠-42

1000 MHz

0.46∠-97

0.06∠22

7.1∠112

0.57∠-48

1250 MHz

0.38∠-115

0.06∠14

6.0∠104

0.50∠-52

Assuming the amplifier s-parameters are designed at a characteristic impedance of Zo=50 0hms, supply voltage is 5V∠0. The source and load impedances of the system be 45 ohms and 70 ohms
Reflection coefficients of the system are
source refelction coefficent= Zs-ZoZs+Zo = 45-5045+50 = -0.0526
load reflection coefficent=Zl-ZoZl+Zo = 70-5070+50 = 0.16667
Let the frequency of operation of the BJT be 750 MHz
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