notes

1. Eeng 360 1
Lecture 5
Superheterodyne Receivers.
Transmitters and Receivers
 Generalized Transmitters
 AM PM Generation
 Inphase and Quadrature Generation
 Superheterodyne Receiver
 Frequency Division Multiplexing

2. Eeng 360 2
Generalized Transmitters
   
     
     
     
   
Re cos
cos sin
Where
c
j t
c
c c
j t
v t g t e R t t t
v t x t t y t t
g t R t e x t jy t


 
 
  
 
 
 
  
Any type of modulated signal can be represented by
The complex envelope g(t) is a function of the modulating signal m(t)
Transmitter
Modulating
signal
Modulated
signal
Example:
( )
Type of Modulation g(m)
AM : [1 ( )]
PM : p
c
jD m t
c
A m t
A e


3. Eeng 360 3
Generalized Transmitters
R(t) and θ(t) are functions of the modulating signal m(t) as given in TABLE 4.1
Two canonical forms for the generalized transmitter:
     
cos c
v t R t t t
 
 
 
 
1. AM- PM Generation Technique: Envelope and phase functions are generated to modulate
the carrier as
Figure 4–27 Generalized transmitter using the AM–PM generation technique.

4. Eeng 360 4
Generalized Transmitters
x(t) and y(t) are functions of the modulating signal m(t) as given in TABLE 4.1
      t
t
y
t
t
x
t
v c
c 
 sin
cos 

2. Quadrature Generation Technique: Inphase and quadrature signals are generated to
modulate the carrier as
Fig. 4–28 Generalized transmitter using the quadrature generation technique.

5. Eeng 360 5
IQ (In-phase and Quadrature-phase) Detector

6. Eeng 360 6
Generalized Receivers
Receivers
Tuned Radio Frequency (TRF) Receiver:
Composed of RF amplifiers and detectors.
No frequency conversion
It is not often used.
Difficult to design tunable RF stages.
Difficult to obtain high gain RF amplifiers
Superheterodyne Receiver:
Downconvert RF signal to lower IF frequency
Main amplifixcation takes place at IF
 Two types of receivers:

7. Eeng 360 7
Tuned Radio Frequency (TRF) Receivers
Active
Tuning
Circuit
Detector
Circuit
Local
Oscillator
Bandpass
Filter
Baseband
Audio Amp
 Composed of RF amplifiers and detectors.
 No frequency conversion. It is not often used.
 Difficult to design tunable RF stages.
 Difficult to obtain high gain RF amplifiers

8. Eeng 360 8
Heterodyning
(Upconversion/
Downconversion)
Subsequent
Processing
(common)
All
Incoming
Frequencies
Fixed
Intermediate
Frequency
Heterodyning

9. Eeng 360 9
Superheterodyne Receivers
Superheterodyne Receiver Diagram

10. Eeng 360 10
Superheterodyne Receiver

11. Eeng 360 11
Superheterodyne Receivers
 The RF and IF frequency responses H1(f) and H2(f) are important in providing
the required reception characteristics.

12. The Mixer
Eeng 360 12

13. The Mixer
Eeng 360 13

14. The Mixer
Eeng 360 14

15. The Mixer: example
Eeng 360 15

16. Eeng 360 16

17. Eeng 360 17

18. Eeng 360 18
Superheterodyne Receivers
fIF fIF
RF Response
IF Response

19. Eeng 360 19
Superheterodyne Receivers

20. Eeng 360 20
Superheterodyne Receiver Frequencies

21. Eeng 360 21
Superheterodyne Receiver Frequencies

22. Eeng 360 22
Frequency Conversion Process

23. Image frequency not a problem.
Eeng 360 23
Image Frequencies
Image frequency is also received

24. Eeng 360 24
Superheterodyne Receiver Typical Signal Levels