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138 EPSON S1C63558 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (FSK Demodulator)
4.15.2 Mask option
The gain of the input amplifier shown in Figure 4.15.1.2 is fixed at 1 (0dB) when the internal feedback
resistor is used.
Use of this internal feedback resistor can be selected by mask option.
When "Use" is selected:
TIP
40kΩ
40kΩ100kΩ
100kΩ
VREF
VREF
100kΩ
100kΩ
Amp
–
+
RING
FB
Fig. 4.15.2.1 Circuit configuration when the internal feedback resistor is used
The gain is fixed at 1 (0dB). Leave the FB terminal open.
When "Not use" is selected (example of differential input):
TIP
Amp
–
+
RING
FB
R
5
R
3
R
6
R
4
R
1
R
2
V
REF
V
REF
500pF
500pF
Fig. 4.15.2.2 Circuit configuration when the internal feedback resistor is not used (example of differential input)
The gain of the amplifier can be changed with external resistors.
A 500 kΩ resistor is recommended for R
1, R2, R5 and R6, and approximately 200 kΩ for R3 and R4.
The gain can be found with the following formula.
G
Amp =
R5
=
R6
(In case of R1 = R2, R3 = R4, R5 = R6)
R
1 R2
When "Not use" is selected (example of single-end input):
TIP
Amp
–
+
RING
FB
RF
RIN
VREF
500pF
Fig. 4.15.2.3 Circuit configuration when the internal feedback resistor is not used (example of single-end input)
The gain of the amplifier can be changed with external resistors.
A resistor of approximately 500 kΩ is recommended for RIN and RF.
The gain can be found with the following formula.
G
Amp =
RF
RIN