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Rev 1.1
11
Theory and Operation
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Theory and Operation
The UHFS module is an instrument-grade, high performance synthesizer with easy to program register-
level control. It functions as a standard synthesized CW source with the added capability of a sweep/list
mode that makes it ideal for applications ranging from automated test systems to telecommunication
equipment to scientific research labs. Being small and modular, it is the ideal solution for system
integration applications that require a high performance RF source. In addition, it could be used as a
general-purpose lab source. Figure 2 shows the block diagram of the device, and the following sub-
sections provide details of its operation.
Figure 2. UHFS block diagram
RF Generation
The UHFS is a 160 MHz to 40 GHz low phase noise, low harmonics, low sub-harmonics, and low spur
synthesizer that uses a hybrid synthesizer architecture comprising of phase lock loops, harmonic
generation, and a DDS functions. Coarse tuning is accomplished by PLL and harmonic generators, while
fine tuning is accomplished with the variable modulus DDS, providing exact frequency generation with
resolution of 1 Hz. Isolation between the internal oscillators, their mixed IF products, harmonics, and
inter-modulation products is accomplished by internal EMI sealed cavities, resulting in improved the
overall phase noise performance and reduction of spurious signal content of this compact size frequency
synthesizer. Synthesized signals are either referenced to an internal 10 MHz OCXO clock, or an external
10 MHz reference source.
Amplitude Control
The output level of the UHFS is controlled through the use of a voltage variable gain amplifier (VVA) and a
step attenuation, the VVA is control via a level DAC. The level is automatically controlled by the device
based on the user level requirement. However, the user may choose to override these settings by
excessing these components, both the leveling DAC and the step attenuator can be control by software
via registers.
N
Fine Step
Gen
REF
IN
REF
OUT
RF1
OUT
10 GHz -
20 GHz
Gen
Harmonic
St ep Gen
VCXO
100 MHz
OCXO
10 MHz
FracN
St ep Gen
2
Subharmonic
Filt ers
ATT
LEVEL
DAC