[opendtv] PNP ATSC tuner to meet A/74

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Tue, 13 Dec 2005 16:19:30 -0500

This is a well written article, which explains what must be
achieved to meet A/74 with a front end that is also cable
ready. The article only talks about the tuner, i.e. analog
RF front end design considerations.


Remember to remove the "3D" characters following any equals

Here's what they say about A/74:

"Today, ATSC A/74(2) is only a 'recommended practice.'
However, as U.S. consumer demand for over-the-air DTV and
HD viewing increase, coupled with an aggressive government
drive to reclaim analog spectrum, many believe it will
become the de facto standard for quality ATSC receiver

Count me among the "many believe."

One comment is that the noise figure they estimate for a
receiver that meets A/74 is 8 dB, (and the new Samsung
ought to beat that by about 2 dB).

They suggest a single conversion tuner with active image
cancellation filter. I think this is the crucial part of the

"Ideally the tuner should achieve a minimum image
cancellation across its operation range of 72.5 dB and a
minimum of 68 dB. This is extremely challenging using
standard tracking filter techniques. To meet the requirement
will either compromise the desired channel filter flatness
or require additional tracking filter stages to achieve
additional image suppression. Neither of these are desirable
since the former may render the tuner performance
unacceptable for other distribution means such as analog
terrestrial or cable and the latter will involve additional
design complexity coupled with increased manufacturing cost.
These issues are potentially compounded when aging and
temperature variation effects are considered. A solution
overcoming these disadvantages is to apply active image
cancellation within the tuner by using image reject mixer
technology in the MOPLL section. With this approach it is
feasible to achieve typically 30 dB of image suppression,
which will ease the tuner tracking filter requirement to
42.5 dB. This helps lower manufacturing costs and is also
far less susceptible to environmental aging."

I'd be curious what others think about this.

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