Further work into the potential effect into the use of dithered
clock oscillators on wideband digital radio services
A report for the Radiocommunications Agency by York EMC Services Ltd, University of York
Authors: D A J Pearce, Prof A G Burr,
T Whitehouse, I D Flintoft
Summary
Recent years have seen the manufacturers of digital electronic
products increasingly utilising dithered clock oscillators (DCO) in
their equipment, primarily as a means of reducing the peak levels of
emissions seen by the detectors used in EMC compliance tests. The study
described in this report modelled a digital broadcast receiver to determine
its immunity to DCO generated interference. The modelled levels were
compared with practical test results obtained from typical digital receivers.
It has been concluded that DCO enabled equipment has a
smaller margin of Electromagnetic Compatibility between it and broadcast
services (analogue or digital) than non-DCO enabled equipment. Furthermore
it was found that the digital receivers investigated were less immune
than might be expected from the modelling: their immunity to both DCO
and CW interference is considered to be dependent on the tuner design.
Two possible approaches to improving the EMC margin have been suggested.
- The existing EMC limits could be reduced for DCO enabled
equipment. This is highly practical in terms of being able to perform
the test with existing methods and equipment. The proposed reductions
would give a significant improvement to the EMC of DVB-T and DAB receivers.
However, it is not known how practical it is to build IT equipment with
these more stringent limits. This would have to be investigated before
the proposed limits could be implemented.
- 2. An alternative approach to improving the EMC of both
DVB-T and DAB receivers is to investigate improving the immunity of
the receivers to DCO interference. The immunity levels of the receivers
tested were not as good as the modelled value. This suggests that the
tuner design might be improved to give superior immunity to DCO noise.
If this approach proved practical then an in-band DCO immunity test
would have to be developed and standardised so that receivers can be
tested to ensure maximum immunity.
Downloads:
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Last Updated: 2006-Feb-01
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