Transcript receivers OF RADIO and TV broadcastING systems

LECTURE 5-6. RECEIVERS OF RADIO AND TV
BROADCASTING SYSTEMS
1.
2.
3.
4.
GENERAL INFORMATION ABOUT RECEIVERS
OF RADIO AND TV BROADCASTING SYSTEMS
MAIN TYPES OF BROADCASTING
RECEIVERS
RECEIVER NOISE FACTOR AND SENSITIVITY
(SENSEPTIBLITY)
MAIN ELEMENTS OF RECEIVERS
5. SOFTWARE DEFINED RADIO (SDR)
1. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV
BROADCASTING SYSTEMS
RS
Sound and (or)
image
transducer
RS+ interference
TX
RX
Оконечное
устройство
Interference
The general block diagram of radio channel of the broadcast and TV systems
A sound or image, is transformed in voltage or current, modulates a high-frequency carrier. As a result the
output radio signal (RS) of TX can be amplitude, phase or frequency modulated U t   U t cos t  t t   t   
0
Interference. At
propagation radio signal in free
space and feed lines it take place
distortions, which are conditioned:
•by irregularity of propagation
medium;
•by the artificial and natural
restriction ;
•by internal noises of antenna and
receiver and its imperfection
Radio receiver (RX) intended for transformation input signals with
the purpose of extraction of useful information.
RX must contain units, necessary for realization of the followings
operations:
•selection from all of aggregate of electric vibrations, pointed in aerial
the external electromagnetic fields, signal from a necessary radio
transmitter;
• amplfication of high-frequency signals;
• demodulation signals;
•strengthening of prorectifying signal.
0

The radio receivers is designed to extraction of useful signals received
from the receiving antenna, its amplification and conversion to the form
required for the normal operation of terminals (loudspeaker, monitor, etc.)
By apointment:
radio broadcasting, TV broadcasting,
communication, navigation, radiolocation, radio control, etc.
By type of signal:
wireless
analog or digital
By the method of signal processing:
- with filter processing;
- with correlation-filter processing.
By frequency band: LF, MF, SF, VHF, UHF, SHF, et cetera
The main functions of radio receivers: the selectivity (separation of the useful
signal); amplification (to the level required for normal working terminal); conversion
(to increase selectivity and stable amplification); automatic gain control (for widening
dynamic rang) ; demodulation (selection of modulation law) or measure the signal
parameters.
Sensitivity - the minimum power or voltage at the input RX, which
provide a given quality of signal processing
Peak (noise-limited) sensitivity - the minimum power Psmin or
voltage Uc min at the receiver input at which the SNR at the output of the
linear part RX equal to one (Ps / Pn = 1 or Uc / Un = 1);
Real (actual or threshold) sensitivity - minimum power or voltage
at the receiver input at which the predetermined reception quality (given
the SNR at the output of the linear part RX).
At wavelength > 1 m, when the resonans circuits RX can be
considered as systems with lumped parameters, the sensitivity is taken
in units of voltage - microvolts or millivolts Uc min. If  <1 m - in terms
of power Pc min.
Real sensitivity radio receiver is in the range of 50 ... 300 μV,
depending on the quality class. Sensitivity of satellite TV receiver can be
-14
-15
up 10 ... 10 W.
For broadcast receivers with ferrite antenna uses the concept of
sensitivity in field strength. It has a value from 0.3 to 5 mV/m.
2. MAIN TYPES OF BROADCASTING RECEIVERS
Block diagram of the receiver of direct amplification
Frequency Converter
. The block diagram of a superheterodyne receiver
f
p
УВЧ
Uc
f
СМ
p
U гр
УНЧ
f г= f р
Гетеродин
Block diagram of direct conversion receivers
SDR RX
Parameters of the radio receivers
Frequency range - the entire band of
frequencies, which can receive signals
Dynamic range RX describes
its ability to receive signals
without distortion
f  f max  f min
Pвых
D,дБ=10 lg(Pinmax/Pin min)
Selectivity: by the frequency (on the next channel, the image channel) by the
waveform, by the polarization
B  PПвх / PПвых
B,дБ  10lg PПвх  10lg PПвых  50...70дБ
у
B зерк
 4f ПЧ

 1  
Q 
 fc

2
Quantitative estimation of noises

Пn 

y
2
 f df



0
0

y f  
П 0,7
1
1  2RCf 
2
1

2RC

a
П0,7
2
П0,7
f
0
2

2
П0,7
П02,7  f
2
df П
2
0,7

0
df
П02,7  f
2


2
П0, 7
dx
1
x 1
 arctg 

2
x
a
a 2a
2
Thermal (heat) noise
Stored energy
1
C
4 RÏ
1
Ý  Ñ U 2n
2
n
1
Э  kT
2
U n2 
1
k T  4kTRÏ
C
n
Nyquist formula
k  1,38  1023
Shot noise
Power rating (nominal power)
Рш 0
Ðn 0  kTÏ
U 2n
R  RL  Рn 0 
4R
n
N0 
I n2sn   2eI0 Пn  I0
Shottky formula
– noise power at matched load
U 2n
Рn 
2Rs  RL 
Un2т   4kTRПn
Рn 0
Пn
3. RECEIVER NOISE FACTOR (figure, ratio)
( Pc / PШ )in
( Pc / PШ )out
INPUT.
UNIT
nRX 
LNA
( Ps / Pn )in
( Рs / Рn )out
nRX  nIN 
IFA
Detector
G
nLNA  1
n 1
nIFA  1
 MIX

... n  d  1/ K
шIN
IN
pIN
К рIN
К рIN K рLNA К рIN К рLNA К рMIX
nRX  nLNA 
If КрIN ≈1
nRX  1  TRX / T0   RX
 RX   LNA 
MIX
 MIX
К рLNA

 IFA
К рLNA К рMIX
 ...
K pIN  1
nMIX  1
nIFA  1

 ...
К рLNA
К рLNA K рMIX
nRX  TRX / T0  1   RX  1
TRX  TLNA 
Т MIX
Т IFA

 ...
К рLNA К рLNA К рMIX
Pn  kTRX Пn  kT0 Пn RX  kT0 Пn (nRX  1)
NOISE OF RECEIVER ANTENNA
*
*
Ta  Ta  TL 1 a 
Т  Т sky  Тatmosphere  Т ground
   5
T  3  30  0.1  250o  60o K
Ta  60 0.9  290 0.1  54  29  83o K
83
T
a  a
a 
 0.25
T0
290
RECEIVERS SENCITIVITY
Noise power output
Рn _ out  Рn _ ant  К р  Рn K p ;
Power output noise, converted to the input
Pn  kTПn  kT0 Пn RX  kT0 Пn (nшRX  1)
 RX  TRX / T0  nшRX  1 →
Рna 
nш   RX  1
U
U
4kTa Ra n


 kT0 a n ;


2 Rа  Rin 4 Ra
4 Ra
2
nа
2
nа
R =Ra
s
Un2т   4kTRПn
RL=Rin
Nyquist formula
U n2
4 KTRn
Pn 
Rн 
 KTn
2( Rs  RL )
4R
T0  3000 K
k =1,38·10-23 W/Hz grad
Рnout  kT0 а n К р  kT0n К рRX nRX  1  kT0n К рRX nRX   а  1;
 a  Ta / T0
Рs min  kT0 Пn nnRX  1   а   kT0 Пn ( RX   а )  kПn (Т RX  Т а )
4. MAIN ELEMENTS OF RECEIVERS
Low-nose amplifier
Wf  exp d f lf 
Ps ( n ) RXin  Ps ( n ) AWf
Balanced frequency converter
Demodulators (detectors)
Uout  KАМ U
— AM
Uout  KFМ f
— FM
Uout  KPМ 
— PM
Amplitude detectors
Сbl >> С
F
D
Uintm
С
HF
RF
F
LF
RL
U LFout
Demodulation of ASK signal
а
б
в
Demodulation of PM signal
Phase detector
VD1
Uout
1
R C
Us/2
U0
kdUd1
0,5
Us
9 0
0
Us/2
kdUd2
Рис.16.13
-0,5
U d1= U 0 + Us /2;

U d2= U0 - Us /2.
U out  К дU 0 1  m 2  2m cos   1  m 2  2m cos 
Us/U0 = m
m << 1
m=1
120
60
Uout
R C
VD2
30

Uout  2 КдUs cos



Uout  2 КдU s  cos  sin 
2
2

Synchronous detector
Output voltage phase detector for in-phase input and reference signals
Uout  2 КдUs
φ =0
is proportional to the input signal Us, and the phase detector is converted in
the synchronous detector. These detectors, due to their high linearity, are
widely used in analog TV for demodulation of the image signals and in
digital TV for demodulating PSK signals.
-1
Рис.16.1
4
150
180 
Frequency detector

Correlated
detector
ucd( )
filter
x
u2(t)
u1(t)
Var. time
delay
u1(t-  )
z ( )   u1 (t )u2 (t   )dt

( Ps / Pn )out  (2 / 1   2 )Kcompr
Kcompr  fin / fout  fin / Пout
PSmin  kT0
fin
(nnRX  1)
Kcompr

compression
expansion
BHF
LNA
MIX
PreIFA
f IF= |f1 – fs |
Bmirr
 4 f IF 
 1  
Q 
f
 s

AGC
BIF
BD
Matched filter –Main IFA
KuIFA 
2
_
X
BLF (BDP)
АD
LFA
PD
ADC
UinDET
PSмin К рBHF
Main IFA
D
S
P
f2
f1
FS
PD
90
Block diagram of the analog – digital receiver
o
ADC
DAC
nnRX
n  1 nnIFA  1
n
1
 nnLNA  nIF

 ...  nADC
К рLNA К рувчK рIF
К р( beforADC )
nnADC
PnADC
For ADC
U 2


Rin 12Rin
n шАЦП  1 
L=8
U max ADCin
7.5 10 
3 2
12  75  4  1021  106
ADC
AD9260
 1.69  10
7
L=16
2L  1
N
 U max PD  U
 U
2
2
N  2L 1
U  2UmахADCout / N  2 *1 / 255 0.0075V  7.5mV
Rin  75
L
For
K p  nnADC
PnADC
U 2
U 2
 1
 1

Pn 0 К рADC
12RinkT0 Пn 12RinkT0 Пn
 n2
1107ПВ2
If only
ADC have not
affected on RX
noise factor
D
N
N
, or D  20 lg [dB]  6L
2
2
FT , MHz
nnADC  1 
D, dB
3 10 
5 2
21
12  75 4  10
 10
6
 200
The twentieth century saw the explosion of hardware defined
radio (HDR) as a means of communicating all forms of audible;
visual, and machine-generated information over vast distances.
Most radios are hardware defined with little or no software
control; they are fixed in function for mostly consumer items for
broadcast reception. They have a short life and are designed to be
discarded and replaced.
Software defined radio (SDR) uses programmable digital devices to
perform the signal processing necessary to transmit and receive
baseband information at radio frequency. Devices such as digital signal
processors (DSPs) and field programmable gate arrays (FPGAs) use
software to provide them with the required signal processing
functionality. This technology offers greater flexibility and potentially
longer product life, since the radio can be upgraded very cost
effectively with software.
Software Defined Radio (SDR)
SDR equipment - these are elements of the wireless network which operating modes and
parameters can be changed or expanded after the elements are made using the software.
Modulated signal
u(t )  A(t ) cos[0t   (t )]
can to present by sum of two quadrature component
u(t )  [ A(t ) cos (t )]cos0t  [ A(t ) sin  (t )]sin 0t  Ac cos0t  As sin 0t 
 I cos0t  Q sin 0t.
A(t ) 
Ac2  As2
 As
 Ac
 (t )  arctg

I 2  Q2

Q


arctg



 I 

Zero IF Quadrature Product Detector
One cycle Sine Wave at Sampled Frequency Fo