MT88E43B
Data Sheet
C1
R1
IN+
IN-
C2
R4
R5
GS
R3
R2
V
Ref
Differential Input Amplifier
C1 = C2
R1 = R4 (For unity gain R5= R4)
R3 = (R2R5) / (R2 + R5)
Voltage Gain
(A
V
diff) = R5/R1 (see Figure 9,10,11)
Input Impedance
(Z
IN
diff) = 2
R1
2
+ (1/ωC)
2
Figure 7 - Differential Input Configuration
FSK Demodulation
The MT88E43 first bandpass filters and then demodulates the incoming FSK signal. The carrier detector provides
an indication of the presence of signal at the bandpass filter output. The MT88E43’s dual mode 3-wire interface
allows convenient extraction of the 8-bit data words in the demodulated FSK bit stream.
Note that signals such as dual tone alert signal, speech and DTMF tones lie in the same frequency band as FSK.
They will, therefore, be demodulated and as a result, false data will be generated. To avoid demodulation of false
data, an FSKen pin is provided so that the FSK demodulator may be disabled when FSK signal is not expected.
There are two events that if either is true, should be used to disable FSKen. The events are CD returning high or
receiving all the data indicated by the message length word.
Item
Mark
frequency
(logic 1)
Space
frequency
(logic 0)
Received
signal level -
mark
Received
signal level -
space
BT
1300Hz
±1.5%
2100Hz
±1.5%
-8dBV to
-40dBV
(-5.78dBm to
-37.78dBm)
-8dBV to
-40dBV
Bellcore
1200Hz
±1%
2200Hz
±1%
-12dBm
1
to
-32dBm
-12dBm to
-36dBm
Table 2 - FSK Characteristics
9
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
