MSK (Minimum Shift Keying) CML Microcircuits, MSK (Minimum Shift Keying) Datasheet - Page 24

• 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
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3.2.3.2 Data Re-timing
The date re-timing block aligns the data to the clock recovered by the PLL. The most common solution is a D flip-flop. The
data is applied to the D input of the flip-flop and the PLL output clocks the data through the flip-flop. A model of a D flip-
flop is shown in section 3.4.
3.3 System Simulations
Figure 30 shows an MSK system consisting of a transmitter, noisy channel, and a receiver. By simulating a complete
system with the models defined above, various signals are plotted in Figure 31. The transmit data bits have a 16 bit
preamble for bit synchronization. The receive filter output shows how noise degrades the band limited MSK signal. This
degradation is more clearly seen in the receive filter eye diagrams, Figure 32 and Figure 33. The discriminator output
clearly shows the need for the post discriminator low pass filter. The unclocked output exhibits jitter (i.e. variable length bit
duration) and shows the need for sampling it in the middle of the bit to reliably recover it. The clocked data output shows
relatively little jitter in the re-timed data. Additionally the carrier detect output and internal signals are shown to help the
reader understand their function. While the transmitter is not enabled many bad zero crossings are indicated. These
keep the sliding window filter output from going below the carrier detect threshold. After the start of transmission few bad
zero crossings are seen and the carrier detect output trips high when the sliding window filter output goes below the
threshold.
© 1997 MX COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
if reset is equal to 1 then {
counter = 0;
late = 0;
early = 0;
}
else increment counter;
INPUT
BITS
Transmitter
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Figure 30: MSK Communications System with Noisy Channel.
MSK
TX
// reset flag is true then reset counter and early and late flags
NOISE
Channel
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MSK
RX
Fax: [phone]
Receiver
OUTPUT
BITS
Doc. # 20830084.001
APPLICATION