[Engineering Feature]
Oscillators Face The Final Frontier
Space applications like satellites present unique sets of challenges that designers need to consider if they want to ensure performance and reliability.
In addition to TID, survival and immunity to latch-up must be considered for single-event upset (SEU) and single-event effects (SEE). There are several databases publicly available with radiation data to help the designer with the proper component selection. Depending on the radiation requirements, the components available may be significantly reduced.
Even when the proper components are selected and utilized, many customers still require lot testing of active devices to ensure the requirements will be met. The use of approved radiation test facilities is necessary for testing at the component level and, in some cases, at the oscillator level.
The effects of radiation in space will affect the performance of the oscillator over its life. Not only do the components need to survive the effects of radiation, but its impact on the parametric values of the components must be well understood as well. Several analyses typically need to be performed on all new designs, such as worst-case circuit analysis (WCCA), end-of-life calculations (EOL), and failure-mode effects analysis (FMEA).
The parametric shifts from radiation need to be utilized in these analyses. Utilization of the functional block design approach mentioned above can significantly reduce the design effort by reusing previously evaluated and proven portions of the circuit.
ASSEMBLY AND TEST PROCESSES The workmanship and quality standards for space products are the most stringent of any industry. These requirements need to be considered at the design stage, not viewed as a requirement for operations to handle. Certain reliability levels, for instance, limit the amount of rework that can be performed on a flight device. Therefore, adequate design margins need to be considered to ensure compliance so requirements can be met within these constraints.
For example, several factors in the design can affect the phase noise performance of the oscillator. For PCB-based (printedcircuit board) designs utilizing PEMs, component replacements to optimize the phase noise performance are very typical. This is not an option with space-level designs since you can very quickly exceed the limit for the number of component replacements, which will result in the unit being scrapped.
Since the devices will be operating in a vacuum, some of the acceptance and screening tests need to be performed in a vacuum in production. The frequency and temperature stability of the oscillator can significantly change when going from ambient pressure to a vacuum. These changes need to be well understood at the design stage so the proper margins can be designed in and the proper ambient pressure targets can be set in production to ensure the specifications will be met in a vacuum (Fig. 3).
The design should also be capable of being manufactured to previously approved processes. In many instances, the assembly and test processes have to be audited and approved by the customer. If design features are going to require new assembly processes and/or test processes, the customer should be involved early in the process validation to prevent delays down the road. Evaluation tools such as real-time x-ray or destructive physical analysis should be used to evaluate and approve new processes.
SUMMARY The challenges of designing oscillators for space are much more complex than commercial or even military markets. These challenges are escalated due to component restrictions, complex specifications, and assembly concerns. The best way to address these issues is to reuse as much content from previously qualified designs to help minimize risk, as well as shorten design cycles and manufacturing lead times.
DAVID BAIL, director of product marketing, obtained his master’s degree in electrical engineering from Syracuse University. He also obtained a bachelor’s degree in engineering physics from the University of Maine and an MBA from Temple University.
We are interested to purchase 1) Oscillator, Crystal Controlled; P/N.224Y0856; Qty 3 each. 2) Crystal Oscillator; P/N. 285Y1173; qty 4 each. End-user: Republic of Singapore Air Force Please advise the following :
Price Condition - New Leadtime Quote validity 120 days Advise the OEM or vendor's name of the C of C which will be given Warranty period Goods with shelf life shall have at least 80% if its shelf life remaining at the time of delivery and they must be individually packed. Shelf life, cure date and other related information will be indicated in the packing list/delivery note which accompany the goods.
Look forward to a reply not later than 29 Aug 2009.
Steve Leong -August 10, 2009
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