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Subject: CMX589A - Using Two-Point Modulation To Reduce Synthesizer Problems When Designing DC-Coupled GMSK Modulators
Data communications systems that employ modulation techniques requiring good low-frequency response place unique
demands on PLL-based frequency synthesizers that are commonly employed for frequency generation and stability.
For example, GMSK and four-level FSK modulation schemes require modulation response extending to DC, an
attribute that is not easily accommodated by many modulators.
This application note discusses the problems encountered when designing GMSK modulators with respect to the
characteristics of characteristics of PLL frequency synthesizers, and illustrates how two-point modulation
can be used to solve them.
[application note link].
FX589 and FX839 Cellular Digital Packet Data (CDPD)
Cellular Digital Packet Data (CDPD) is a packet data transfer system currently employed to provide a
digital data facility to run in parallel with the existing analogue AMPS cellular radiophone system using
current frequencies and RF infrastructure.
Reusing AMPS infrastructure provides the CDPD system and therefore its participants with the same,
wide geographical coverage as the cellphone voice network. CDPD supports such common protocols as
TCP/IP and OSI/CLNP.
[application note link].
Subject: FX589 GMSK Modem Applications
This application note is to be read in conjunction with the current FX589 Data Sheet. This document is
issued to clarify points in currently published documents and to present new information that will enable the
user to easily understand and implement this GMSK product.
[application note link].
MX589 Practical GMSK data transmission
The proliferation of computers in today's society has increased the demand for transmission of data over
wireless links.
Binary data, composed of sharp "one to zero" and "zero to one" transitions, results in a spectrum rich in
harmonic content that is not well suited to RF transmission. Hence, the field of digital modulation has been
flourishing.
Recent standards such as Cellular Digital Packet Data (CDPD) and Mobitex specify Gaussian filtered Minimum Shift Keying (GMSK) for their modulation method.
[application note link].