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3.3 Input Amp Circuit
3.3.1 Differential Input
The amp at the input stage must have its circuit configured to allow gain to be set correctly. For this reason, it
requires five to six external resistors.
TIP
RING
The gain in the input amp can be set depending on values R
replaced by one resistor.
G
A MP
To set the FSK and CAS tone signal-detection levels, determine each resistance value with respect to V
below.
V
is the power supply voltage fed to the V
DD
using a resistance of about 200 kΩ for noise prevention.
Tables 3.3.1 and 3.3.2 show typical resistance values and amp gain for the case where V
respectively. Do not use resistors with lower values than those shown in the table below when the MODE1 pin is set
to 1 (FSK detection during power down).
Parameter
R
, R
1
2
R
, R
3
4
R
, R
5
6
Input amp gain
FSK/CPM - CD ON level (Typ.)
FSK/CPM - CD OFF level (Typ.)
CAS - CD ON level (Typ.)
Parameter
R
, R
1
2
R
, R
3
4
R
, R
5
6
Input amp gain
FSK/CPM - CD ON level (Typ.)
FSK/CPM - CD OFF level (Typ.)
CAS - CD ON level (Typ.)
S1C05251 TECHNICAL MANUAL
V
REF
R
4
R
2
R
1
R
3
V
REF
Figure 3.3.1 Input amp circuit
R
R
5
6
=
=
[times]
R
R
1
2
R
R
5
G
=
=
A MP
R
R
1
pin of the S1C05251. For R
DD
Table 3.3.1 Resistance values and gain (V
Bellcore
1000 kΩ
200 kΩ
562 kΩ
0.562 times (-5 dB)
-43.0 dBm
-45.0 dBm
-35.9 dBm
Table 3.3.2 Resistance values and gain (V
Bellcore
1000 kΩ
200 kΩ
338 kΩ
0.3372 times (-9.4 dB) 0.3372 times (-9.4 dB)
-43.0 dBm
-45.0 dBm
-35.9 dBm
FB
R
6
INN
–
Amp
INP
+
R
5
V
REF
to R
as shown below. Note that R
1
6
(W hen R
= R
, R
1
2
3
V
6
D D
× 0. 5 62 [times]
=
5
2
and R
3
= 5 V)
DD
Value
BT
1000 kΩ
200 kΩ
562 kΩ
0.562 times (-5 dB)
-45.2 dBV
-47.2 dBV
-44.1 dBV
= 3 V)
DD
Value
BT
1000 kΩ
200 kΩ
338 kΩ
-45.2 dBV
-47.2 dBV
-44.1 dBV
EPSON
3 FUNCTIONAL DESCRIPTION
To filter
and R
may be
3
5
= R
, R
= R
)
4
5
6
DD
, Seiko Epson recommends
4
= 5 V and V
DD
DD
Condition
1%
1%
1%
Tone filter gain = -4 dB
Condition
1%
1%
1%
Tone filter gain = -4 dB
as shown
= 3 V,
13
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