MT88E41
1.4
Carrier Detect
Data Sheet
The presence of the FSK signal is indicated by a logic low at the carrier detect (CD) output. This output has built in
hysteresis to prevent toggling when the received signal is shortly interrupted. Note that the CD output is also
activated by voice since these frequencies are in the input frequency detection band of the device. The user may
choose to ignore this output when FSK data is not expected, or force the ECNIC into its powerdown mode.
MT88E41
OSC1 OSC2
MT88E41
OSC1 OSC2
MT88E41
OSC1 OSC2
3.579545 MHz
to the
next MT88E41
Figure 5 - Common Crystal Connection
1.5
Crystal Oscillator
The ECNIC uses a crystal oscillator as the master timing source for filters and the FSK demodulator. The crystal
specification is as follows:
Frequency:
Frequency tolerance:
Resonance mode:
Load capacitance:
Maximum series resistance:
Maximum drive level (mW):
e.g. CTS MP036S
3.579545 MHz
±0.1%(-40°C+85°C)
Parallel
18 pF
150 ohms
2 mW
A number of MT88E41 devices can be connected as shown in Figure 5 such that only one crystal is required. The
connection between OSC2 and OSC1 can be D.C. coupled as shown, or A.C. coupled using 30pF capacitors.
Alternatively, the OSC1 inputs on all devices can be driven from a CMOS buffer (dc coupled) with the OSC2 outputs
left unconnected.
1.6
VRef and CAP Inputs
V
Ref
is the output of a low impedance voltage source equal to V
DD/2
and is used to bias the input op-amp. A 0.1µF
capacitor is required between CAP and V
SS
to suppress noise on V
Ref.
6
SEMICMF.019
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
