MSK (Minimum Shift Keying) CML Microcircuits, MSK (Minimum Shift Keying) Datasheet - Page 14

• 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 MSK Demodulation
MSK Demodulation is the process of converting Sinusoids to digital data. MSK demodulation looks for specific
frequencies that represent digital data. Shown in Figure 14is a block diagram for a typical MSK demodulator. MSK
demodulation can be broken down in to three sections, signal demodulation, bit synchronization and MSK carrier
detection.
3.2.1 Demodulator
The MSK detector demodulates the digital information from the received analog signal. There are six blocks that make up
the detector. Each block processes the output of the previous block. The output of the sixth block is recovered digital data.
The blocks are listed below and will be discussed in order of signal progression.
3.2.1.1 RX Filter
The receiver’s input filter is a band pass filter centered around the main lobe of the MSK spectrum. It is designed to have
a passband width equal to the bit rate (i.e. 2100-900 = 1200Hz and 3000 - 600 = 2400Hz). The frequency domain
© 1997 MX COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
p[i+1] = fractional remainder of p i
}
(a) Input Receive Filter
(b) Zero Crossing Detector
(c) Monostable
(d) Discriminator
(e) Post Discriminator Low Pass Filter
(f) Data Slicer/Comparator
output N i n
Receive
Input
Input
Receive
Filter
sin 2
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c
Zero
Crossing
Detector
Figure 14: MSK Demodulation Block Diagram.
4.0
dk
Demodulation
c
N
n
4.0
dk
p i
;
Invalid
Zero
Crossing
Indicator
Mono-
Stable
;
14
// calculate phase constant for next input bit
Carrier Detection
Sliding
Window
Averager
Discrim-
inator
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Digital
PLL
Bit Synchronization
Comparator
w/Hysteresis
Post
Detect
Filter
Fax: [phone]
Data
Retiming
Compar
-ator
Clocked
Data
Output
Clock
Output
Carrier
Detect
Output
Unclocked
Data
Output
Doc. # 20830084.001
APPLICATION