This document discusses concepts in RF system design, including active RF components like transistors and basic RF concepts. It covers the frequency range of RF, semiconductor materials used in RF like GaN, GaAs, and SiGe. Specific RF devices discussed include Schottky diodes, which are used in RF detectors, mixers, oscillators and amplifiers due to their smaller junction capacitance. Bipolar junction transistors (BJTs) and field effect transistors (FETs) are also covered, noting that BJTs are widely used in RF applications due to their low cost, operating frequency, low noise performance and high power handling capacity through specialized construction designs.

1. EC8651 TLRF
UNIT – 5
RF SYSTEM DESIGN CONCEPTS
By
Sk. Hedayath Basha

2. Syllabus
• Active RF components: Semiconductor
basics in RF, bipolar junction transistors,
RF field effect transistors, High electron
mobility transistors
• Basic concepts of RF design, Mixers,
Low noise amplifiers, voltage control
oscillators, Power amplifiers, transducer
power gain and stability considerations.

3. Basics of RF
• RF - Radio Frequency
• The range of Radio Frequency is 300 MHz to
1GHz ( - Reference Book)
• The RF range in Google is 20KHz to 300 GHz

5. Semiconductor Basics in RF
• Silicon is still the dominant material in
semiconductor manufacturing.
• However, other materials are more compatible
with the high signal frequencies present in RF
systems.
• Three alternative materials that are used in RF
semiconductors are gallium nitride (GaN), gallium
arsenide (GaAs), and silicon germanium (SiGe).
• Specialized semiconductor technologies make it
possible to fabricate devices that maintain
adequate performance at extremely high
frequencies, i.e., above 100 GHz.

6. RF Diodes
• The Classic PN Junction diode is not suitable for
high frequency applications because of high
junction capacitance.
• Diodes formed by a metal-semiconductor
contact posses smaller junction capacitance and
used in high frequencies.
• Schottky diode is one of the metal-
semiconductor diode used in RF detectors,
Mixers, attenuators, Oscillators, and amplifiers.

7. Cross sectional View of Schottky Diode

10. BJT
• The transistor has proliferated into a wide
host of sophisticated types ranging from
the still popular bipolar junction transistors
(BJTs) over the modern GaAs field effect
transistors (GaAs FETs) to the most recent
high electron mobility transistors (HEMTs).

11. BJT Construction
• The BJT is one of the most widely used active
RF elements due to
a) Low Cost Construction
b) Relatively high operating frequency
c) Low noise performance
d) High power handling capacity

12. • The high power capacity is achieved through a
special inter digital emitter- base construction
as part of a planar structure.