MSK (Minimum Shift Keying) CML Microcircuits, MSK (Minimum Shift Keying) Datasheet - Page 20

• Manufacturer Part Number: MSK (Minimum Shift Keying)
• Description: Minimum Shift Keying and its Application to Wireless Data Transmission
• Manufacturer: CML Microcircuits

MSK and its Application to Wireless Data Transmission
3.2.2.1 Bad Zero Crossing Detector
The Bad Zero Crossing Detector monitors the zero crossings of the filtered input signal. The time between zero crossings
is compared against a referenced. If the Bad Zero Crossing Detector determines that a zero crossing is not properly time
spaced the output pulses high, otherwise the output remains low. Figure 24 and Figure 26 show the timing windows used
for 1200 and 2400 baud. Figure 25 and Figure 27 show that with a properly timed input signal (i.e. zero crossings within
the window) the output is low. With an improperly timed input (i.e. zero crossing outside the window or end of window
reached) the output pulses high. The windows are based on the ideal zero crossing spacings +/- 5% of the bit time. Thus
each baud rate would have two valid windows, however the receive input filter introduces a slight intersymbol interference
at symbol boundaries and thus the windows need to widen towards each other to account for this. Since the windows of
the 1200 Baud case become very close, a single window is used.
© 1997 MX COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tele: 800 638-5577 910 744-5050
Figure 24: 1200 Baud Valid Zero Crossing Window
Figure 25: 1200 Baud Bad Zero Crossing Detector.
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Doc. # 20830084.001
APPLICATION