Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 141
EM6E
9.
The basic compander configuration is given above. From the
diagram, one can understand the factor of two of companding
as follows:
There is a variable gain cell (variable resistor) in the feedback
loop of an OpAmp (NJM4565M) that is controlled by the
rectifier cell that detects the output voltage of the OpAmp and
translates it into a current send to the gain cell. The rectifier has
an attack time constant (C3) and a decay time constant (C4),
which is optimised to give the best auditive result.
If the input (Vin) rises with e.g. 4 times then the output can rise
only 2 times. This is because the feedback resistor formed by
the gain cell is decreased with a factor of two.
Remember that for an OpAmp Vout= Vin*((Rf+R1)/R1), where
R1 is constant (Rf= R2+internal gain cell resistance).
The Pre-Emphasis, Stereo Encoding, and Output Filtering
The two channels that are available from the compander are
now having pre-emphasis with a time constant of 12
µ
s. Too
much time constant would give problems with the voltage rising
too high at maximum modulation frequency, and hence
occupied bandwidth of the modulated signal. The pre-
emphasis consists of a simple RC circuit. The stereo encoder
7111C is in fact just an electronic switch, which is driven by the
sub carrier frequency. With this operation, the frequency
spectrum at the output of the switch is as follows in the
frequency domain:
Figure 9-15 Stereo encoder circuitry
Figure 9-16 Stereo encoding frequency spectrum
Note that the other two switches of 7111 (respectively 7111A
and 7111B) are not used.
L+R
L-R
L-R
Subcarrier freq.
L
R
20kHz 46.875kHz 66.875kHz
Multiplex without pilot
CL 36532008_076.eps
090503
&
3
9
11
13
CT
CT=0
1
Z1
+
STEREO
CODER
3
2
1
8
4
10K
3189
7116-A
NJM4565M
3187
22K
NJM4565M
7113-A
3
2
1
8
4
F147
3164
3K3
3191
220R
3190
220R
2196
3n9
BC847B
7121
2174
47p
2170
470p
15K
3175
220p
2177
100n
2182
18K
3151
22n
2165
18K
3152
16V
10u
2171
2195
1n2
8K2
3178
2194
1n5
18K
3150
6K8
3172
2134
33p
F124
4M
1106
AT-51
4u7
2168
2167
220u
82p
2173
3K9
3177
1K0
3183
F125
F131
16V
10u
2153
F144
F145
22p
2151
F150
5
6
7
8
4
3188
4K7
7113-B
NJM4565M
2K2
3131
F146
100n
2135
3169
10K
3165
3K3
680R
3161
2137
100n
100p
2202
4106
BLM21
5133
BC847B
7118
680R
3160
2154
10u
16V
22p
2152
5126
BLM21
100n
2136
27K
3173
22n
2166
2175
1u
F126
3171
680K
2178
22n
BLM21
5125
4105
7
Vss
8
Y0
5
Y1
3
Z
4
11
10
16
VDD
74HC4053D
7111-C
E
6
S
9
Vdd
16
Vee
9
8
GND
12
1
2
3
7
5
4
6
14
13
15
74HC4060
7110
18K
3153
F130
3166
39K
2183
100n
2169
33p
F148
Y1
1
Z
15
Y1
14
Z
74HC4053D
7111-B
E
6
S
10
Vdd
16
Vee
7
Vss
8
Y0
2
7111-A
74HC4053D
6
E
11
S
16
Vdd
7
Vee
8
Vss
12 Y0
13
7116-B
5
6
7
8
4
NJM4565M
F149
33p
2133
10K
3132
3179
10k
680p
2172
15K
470p
2176
3176
82K
3149
270K
3130
7119
BC847B
5130
220u
390R
3182
7120
BC857B
8K2
3174
+8V
+8b
pilot
+5V
subc
Vpil
mon_ster
subc
MPX
+8V
+8V
+8V
+8V
+8V
+8V
pilot
+5V
+5V
+5V
+5V
CL 36532008_077.eps
290403
MODULATION
LEVEL
Summary of Contents for 28PW9618
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Page 19: ...Directions for Use EN 19 EM6E 3 ...
Page 62: ...62 EM6E 7 Circuit Diagrams and PWB Layouts Small Signal Board Diversity Tables ...
Page 118: ...118 EM6E 7 Circuit Diagrams and PWB Layouts Personal Notes ...
Page 172: ...Revision List EN 172 EM6E 11 11 Revision List First release ...