TK10651MTL TOKO, TK10651MTL Datasheet - Page 8

• Manufacturer Part Number: TK10651MTL
• Description: LOW VOLTAGE COMPANDOR
• Manufacturer: TOKO

TK10651
USING THE COMPANDOR TO IMPROVE S/N (CONT.)
Page 8
The improvement resulting from the expander is expressed
by measuring the overall characteristics of the FM IF
System (TK10487M). The signal generator was switched
to internal modulation and the output is defined as 0 dB
when the RF input = 80 dB . As the graph below indicates,
the noise is reduced when the expander is used, and good
S/N ratio is maintained even when the RF signal input is
weak.
Finally, the overall characteristics are measured using both
the compressor and the expander. The output is measured
when the compressor's input is at –40 dB V and the
frequency deviation is 3.0 kHz.
The graph below shows the characteristics when the RF
input is strong (RF IN = 80 dB ). The dynamic range is
increased by more than 12 dB when the compandor is
used.
-10
-20
-30
-40
-50
-60
-70
-80
0
-10
-20
-30
-40
-50
-60
-70
-80
-20
10
0
-120
OUTPUT VOLTAGE RATIO vs.
OUTPUT VOLTAGE RATIO (FOR
STRONG RF INPUT SIGNAL)
COMPANDOR RF INPUT
0
vs. COMPANDOR RF INPUT
-90
20
V IN (dBu)
TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)
V IN (dBV)
-70
40
-50
60
SIGNAL
NOISE
-30
80
-10
100
DASHED LINE: THROUGH
FILTER : CCITT P.53
NO PRE-EMPHASIS
f OSC = 10.245 MHz
DASHED LINE: THROUGH
OR DE-EMPHASIS
IF IC : TK10487M
DEV =
f MOD = 1.0 kHz
COMPRESSOR
FILTER : CCITT P.53
NO PRE-EMPHASIS
SOLID LINE:
V CC = 3.0 V
f OSC = 10.245 MHz
OR DE-EMPHASIS
IF IC :TK10487M
f MOD = 1.0 kHz
COMPRESSOR
SOLID LINE:
V CC = 3.0 V
3.0 kHz
The following graph shows the characteristics when the RF
input is weak (RF IN = 30 dB ). There is a great difference
when the compandor is used with a weak RF input. When
the through function is used (noise reduction off), the output
is lost in noise as the compressor input drops below –80
dBV; but when the compandor function is used, it remains
level below –100 dBV. With a weak RF input, dynamic
range is extended by 30 dB.
The effects of the compandor within a narrow band FM
communications system was demonstrated while a coaxial
cable was used in place of transmission through free
space. The signal source was an FM signal generator
although there are some differences when actual transmis-
sion is through free space. However, the test configuration
used in this experiment is useful in understanding the
effects of the compandor.
-10
-20
-30
-40
-50
-60
-70
-80
10
0
(FOR WEAK RF INPUT SIGNAL)
-110
OUTPUT VOLTAGE RATIO
vs. COMPANDOR INPUT
-90
V IN (dBV)
-70
-50
-30
-10
January 2000 TOKO, Inc.
DASHED LINE: THROUGH
FILTER : CCITT P.53
NO PRE-EMPHASIS
f OSC = 10.245 MHz
OR DE-EMPHASIS
IF IC :TK10487M
COMPRESSOR
f MOD = 1.0 kHz
SOLID LINE:
V CC = 3.0 V