MT88E43B
Data Sheet
R1
R4
IN+
IN-
C1
C2
R5
GS
R2
R3
VRef
Differential Input Amplifier
C1 = C2
R1 = R4 (For unity gain R5= R4)
R3 = (R2R5) / (R2 + R5)
Voltage Gain
(A diff) = R5/R1 (see Figure 9,10,11)
V
Input Impedance
R12 + (1/ωC)2
(Z diff) = 2
IN
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
BT
Bellcore
Mark
1300Hz
1200Hz
frequency
(logic 1)
±1.5%
±1%
Space
2100Hz
2200Hz
frequency
(logic 0)
±1.5%
±1%
Received
signal level -
mark
-8dBV to
-40dBV
-12dBm1 to
-32dBm
(-5.78dBm to
-37.78dBm)
Received
signal level -
space
-8dBV to
-40dBV
-12dBm to
-36dBm
Table 2 - FSK Characteristics
9
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
