 Phase Coherent Multi-channel RF Synthesis
May 12, 2009
Jason Breitbarth and Joe Koebel, Holzworth Instrumentation
The phase-locked loop (PLL) has been widely used in traditional tunable RF synthesis design to maintain a “fixed” phase relationship between a generated (output) frequency and that of a reference signal. Although a properly designed PLL is an effective method for maintaining a fixed frequency, it does not allow for fully monotonic phasing in applications where phase coherence is critical.
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INTRODUCTION
Multi-channel synthesis applications require specific performance parameters
that are often overlooked with the design of single channel synthesizer systems.
Performance specifications for multi-channel synthesis applications typically
require channel to channel, short and long term phase coherence that is not
possible with phase-locking an N-number of single channel synthesizers
together. This configuration only creates a long term phase-lock ‘average’
between the outputs. Each individual synthesizer also contributes to the short
term stability of this system, which is problematic with traditional phase locked
synthesizers.
Holzworth Instrumentation has taken a new design approach to the multi-channel
synthesis system. The unique architecture of Holzworth’s single channel series
of synthesizers actually provides optimal performance in a multi-channel
synthesis environment due to the elimination of the PLL. These non-PLL
synthesizers provide superior channel to channel short and long term phase
stability and phase coherency. The compact size, relative low cost and high
performance of a single channel has enabled Holzworth to provide four and eight
channel synthesizer modules with independently tunable channels that consume
only 1U of space in a 19 inch rack.
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