[opendtv] Re: opendtv Digest V2 #24

> From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
> Subject: [opendtv] Re: Latest S/N test
> Date: Thu, 27 Jan 2005 15:13:13 -0800
> 
<...>
>
> Zarlink recently announced design of a single ended tuner
> for Thompson that they say exceeds the ATSC's A74
> recommendation. That is nothing exceptional given that it
> is a marginal spec. I was advised last year that Zarlink, RMT,
> and others, supply triple conversion receivers, with significantly
> better specs than A74, to the European COFDM markets,
> where they are serious about OTA performance.
> See these web page.
> http://products.zarlink.com/product_portlets/thomson_pnp.htm
> http://www.rwt.com.uk
> 
> Tthe Zarlink spec sheet doesn't give one a clue
> about how their single conversion image rejection scheme
> functions but I did note that the Noise Figure is a paltry 13db.
> As I recall, the DVB-T spec. is  8db or less and a typical
> DVB receiver is in the 5db range.

RWT (correctly rwt.co.uk) designed the SetPal tuner which helped enable the
UK DTT 'Freeview' market in 2002 with the first < GBP 100 STBs. SetPal-1
used double conversion with Zarlink tuner chips, autonomous wide band RF
AGC derived after a discrete LNA (overall NF 4dB) and a broad
alignment-free tracking filter to reduce mixer IM loading, a 1220MHz 1st IF
with AGC and a 36MHz final IF with AGC. Overall phase noise was in fact
lower than with single-conversion designs because the 1270-2080 MHz
upconversion VCO PLL could use a wide-band loop with 4MHz comparison
frequency (for an 8MHz channel matrix). The downconverter needed to tune
only a handful of 41.667 kHz steps, so a narrow loop could be used here.

The later SetPal-2 uses the Zarlink image-rejection MOPLL in a
single-conversion design with wide band RF AGC and alignment-free tracking
filter. As will all consumer MOPLL devices an LNA is required for the
required NF. SetPal-2 features in several current brands of STB, iDVCR,
iDTV and DVR, including products which combine DAB radio.

Conventional DTT tuners (i.e all the others, I believe) in the UK use
single conversion with narrow tracking filters, derived from standard
analog tradition, but with improved-phase-noise converter chips (Philips,
Infineon) for digital. These, as with all consumer analog TV tuners
worldwide, incorporate a simple tracking filter of nominally 12 to 15 MHz
bandwidth, which is production-line tuned by bending coils or 'goalpost'
wire loops until a response template is met. Inevitably tracking is
sub-optimal, and in-channel slope, as well as NF, can be quite high, which
limits ACI protection as well as sensitivity.

SJB

 
 
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