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:

FB

VREF

 

40k

100k

 

100k

TIP

100k

Amp

RING

+

100k

40k

VREF

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):

 

VREF

FB

 

R4

R6

500pF

R2

TIP

 

 

 

 

RING Amp

500pF

R1

+

 

 

R3

R5

VREF

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.

A500 kΩ resistor is recommended for R1, R2, R5 and R6, and approximately 200 kΩ for R3 and R4. The gain can be found with the following formula.

GAmp =

R5

=

R6

(In case of R1 = R2, R3 = R4, R5 = R6)

R1

R2

 

 

 

When "Not use" is selected (example of single-end input):

 

FB

 

RF

500pF RIN

TIP

 

 

RING Amp

 

+

VREF

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.

GAmp =

RF

RIN

138

EPSON

S1C63558 TECHNICAL MANUAL