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Front End (TUNER)

Discussion in 'Electronic Design' started by Myauk, Mar 23, 2007.

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  1. Myauk

    Myauk Guest

    I had a chance to take a look of a typical analogboard circuit diagram
    of a system having Television Receiving unit.
    There is a tuner front end mounted on the analog board.
    Accoring to circuit diagram, there is the antenna connection into the
    front end module and SIF and CVBS output from it. It is controlled by
    I2C input.
    What I would like to know there is why the front end needs a voltage
    as high as 33V.
    And I would like to know the I2C control scheme (how it is controlled
    digitally, and what are the parameter that can be controlled in the
    tuner?) of the Tuner Front End Module.
    Although I google the data, until know I only got the general
    conceptions or overview of the Front End System.
    I would like to have the basic information to design such Tuner Module
    with I2C control scheme to expand the scope of design knowledge.
    Can anybody show me the way or the site or anything?
  2. Phil Allison

    Phil Allison Guest

    ** Massive Groper ALert !

    ** For the "varicap" diodes.

    The gizmos that actually tune the RF circuits inside the tuner module.

    ** Operating frequency, switching bands ....

    All RF stuff you have not got the faintest about.

    ........ Phil
  3. Xceive's part doesn't need much external RF stuff ... just hook up the
    antenna and go.

    The SIF signal on the module you have is really 2nd sound I.F. (4.5,
    5.5, 6.0 or 6.5 MHz, depending upon the channel standard) You will
    need to connect an analog audio demodulator IC to this signal if you
    want stereo.

    If you want to learn more about I2C control of the PLL synthesizer
    inside the tuner, open the tuner can and look up the data sheet for
    the chip connected to the SDA and SCL signals.

    I'm not sure tuner design is something you can reference on the web in
    one neat package. Where would you like to start?

  4. What's the part number of the module?

    Most of the well known vendors have data sheets available describing
    their I2C interface. If what you want is a description of the innards,
    there might be a block diagram or two as well. The details are probably
    a little more difficult to come by. But its almost not worth trying to
    reverse engineer something you can buy so easily.
  5. Myauk

    Myauk Guest

    Thank you so much for the information.
    Now I managed to find an application note for a DVB-T Tuner from
    I intended to expand my scope of knowledge. (not in depth in RF)
    What I am interested there is how to configure the settings for
    respective blocks in the tuner.
    I am quite eager to know how the I2C serial bit stream is recognized
    by different control blocks in the front module.
    And I wish to know the scheme that the processing unit sends commands
    to the front end module, and how it understands the commands from the
    programming point of view.
    With RF receiving system, I understand the basic block diagram but
    wish to know more about it.
    I am not going to design a front end module but I am interested in the
    power supply (usually 5 to 33V boost converter) of it.
    I would like to have the relationship between the power supply
    specifications and the tuner performance.
    However, now I have one applications notes which encourages me to find
    more information on it.
    Thans for your initiation.
  6. IIRC to run the tuning diodes through the full range.
  7. Joerg

    Joerg Guest

    Easy to buy, yes. But don't always expect a whole lot of dynamic range.
    With some tuners that I wanted to use I got the impression that their
    designers didn't know what a dynamic range is.
  8. Phil Allison

    Phil Allison Guest


    ** Do tell us more.

    The TV and FM tuner modules I have used seemed well optimised for their

    Maybe you expected something more.

    ....... Phil
  9. I can see where Joerg is coming from ... I recently completed a gig
    where I needed to work with TV tuners and TV manufacturers. TV tuner
    dynamic range is being compromised lately by some tuner manufacturers.
    The best manufacturers of "can" analog tuners I found were LG and

    TV tuner on-a-chip companies like Xceive have even poorer IP3 ratings.
    Here is an overview of a linearity test:

    The prevailing architecture in most modern TV's seems to favor a "can"
    down converter, e.g. Sancy ($2.25), followed by a digital bandwidth
    SAW, e.g. Epcos. The rest is done in the demod chip. This architecture
    is compatible with both analog and digital broadcasts.

    There are still large manufacturers designing new analog-only TV's,
    some of which incorporate the can tuner + 2nd SIF output; however,
    pricing pressure is favoring Xceive to win the tuner
    market if they can improve dynamic range performance.

    I still have a 197? Sony Trinitron with a clunk-clunk VHF tuner and a
    vernier dial for the UHF. Nice picture, good tuner - no varactors.

  10. joseph2k

    joseph2k Guest

    My best estimation:
    the i2c stream specifies well published channel frequency,
    the uC running the tuner tunes the Local Oscillator (LO),
    the IF appears on the output,
    some automatic frequency control (AFC) trims it to exact tuning,
    This is not the way "it used to be". I remember my dad manually re-tuning
    the "slugs" on an TV back in the day of mechanically switched tuners.
    There were may iterations of "typical" implementations in the intervening
  11. It's a little more complicated. The OP's tuner has a CVBS and 2nd SIF
    output, which means there is an integrated PIF/SIF processor as well
    as the PLL for the L.O. Parameters that get set for the PIF/SIF
    Wideband AGC takeover point
    NEG/POS video modulation
    2nd SIF frequency (on multi-standard types)
    I.F. AGC takeover point
    hi or low-side injection (e.g. L vs L')
    SIF bandwidth

    Frank Raffaeli
  12. Joerg

    Joerg Guest

    It's been too long ago since I gave up on TV tuners (mid 90's) because
    of dirt poor 3rd order IP. After hearing from other engineers that is
    has gotten even worse I never looked back.

    If you find a really good one again please let us all know. One of them
    I investigated further and I found a wimpy dual-gate running at 5mA or
    so in front. That won't hold any water with strong signals.

    Yeah, probably. But what really miffed me was this: Placed the antenna
    on a mast after re-roofing the house. So, I equipped it with a nice
    preamp, splitter, postamps with eight outputs and a home-run style
    wiring closet. It cost a bit but I wanted to do it right. I was very
    diligent with the gain distribution plan as well.

    Hooked up a professional grade receiver to see how FM and stuff comes
    in. Sweet, could now get Bay Area stations etc. Listened to the audio on
    a few TV channels and found that I had now lots more than ever. Then I
    turned on the TV and it was pandemonium. Utter disappointment. All
    channels pumping with noise like crazy, not even the local stations
    showed clearly, audio either not there or completely garbled. Tried the
    downstairs TV, same thing. Then through the VCR's tuner, same thing. I
    had to attenuate by more than 10dB plus place a notch on a strong local
    channel 29 station, plus another channel I don't remember, plus notch
    out the complete FM band. It was pathetic. The result is that we don't
    have a single additional station from when the antenna was on the roof
    (with a shot preamp). Oh well, most TV programming ain't worth it anyhow.
  13. Phil Allison

    Phil Allison Guest


    ( snip drivel)

    ( snip drivel)

    ** What the **** does that mean ?

    ** And then this ASS blames his TV set's tuner for the bad outcome.

    Pathetic really.

    ........ Phil
  14. I presume you meant to say that the performance of most preamps would
    limit linearity, and would dominate IP3, etc. over the tuner. That's
    true, although I've seen some that don't ... I've designed some that
    don't; maybe Joerg used a commercial model.

  15. Phil Allison

    Phil Allison Guest

    "Frank Raffaeli"
    "Phil Allison"

    ** Do not presume.

    Do not alter context.

    ....... Phil
  16. Joerg

    Joerg Guest

    Well, yeah. If a lab grade receiver works just fine and the TV on the
    same antenna is turning into a hopeless pile of intermodulation it's
    pretty clear that the TV isn't up to snuff. Which didn't surprise me. I
    just didn't expect it to be this bad.
  17. Phil Allison

    Phil Allison Guest

    "Phil Allison"

    ** Absolute BOLLOCKS.

    You did a bunch of stupid things that fouled up the whole band for a TV

    Find out the difference between AM and FM - sometime.

    Find out the difference between a TUNED pre-amp and a whole TV band one.


    ........ Phil
  18. Agreed. Did you do any tests on the TV tuner? IP2, 2-tone IM, etc.?
    Did it use a solid state tuner or a "can"?


  19. TV tuners used to be built to accommodate the wide range of signal
    levels from over the air TV reception. Now, they "Assume" that every TV
    will be connected to Cable, DVD, VCR or SAT, all of which have a higher
    than 0 DBM signal level, and never over +10 DBM, so they don't give a
    damn about the dynamic range. Also, some TVs had an extra IF stage that
    would help in far fringe areas. That was why a cheap portable would
    give a better picture than a console. Portables were expected to have a
    wider range of signal levels to deal with, and the design reflected

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  20. Ignore the troll hiding below the Equator.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
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