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Input stage

Discussion in 'Electronic Design' started by Thoma HauC, May 22, 2004.

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  1. Thoma HauC

    Thoma HauC Guest

    Hello,

    Is there someone which could give me a link to a low distortion (-80dB) and wide
    band (200MHz) input stage ?

    Thank you in advance

    Thoma
     
  2. Jim Thompson

    Jim Thompson Guest

    What's an "input stage"?

    ...Jim Thompson
     
  3. James Meyer

    James Meyer Guest

    input stage........................first stage

    output stage.......................last stage

    intermediate stage.................any stage between the input and output stage

    silver stage.......................the movies

    Jim
     
  4. John Larkin

    John Larkin Guest

    200 MHz. Must be audio.

    John
     
  5. Reg Edwards

    Reg Edwards Guest

    The lower the input signal the lower the distortion. Nothing to worry
    about.

    To obtain wide band up to 200 MHz use a low power, dual gate FET with a
    drain load of one or two hundred ohms. So expect a very low stage gain. You
    may have to use 2 or more stages for small signal levels. Keep stray
    capacitance to its lowest possible level.

    You are attempting the nearly impossible if you want anything to be flat up
    to 200 MHz. Negative feedback and even lower stage gain MIGHT do the job.
     
  6. Tam/WB2TT

    Tam/WB2TT Guest

    You might want to check out Minicircuits. Motorola also made modules like
    that, but I don't know who would make these now. If not Mote, possibly ON or
    Tyco. Communication Concepts and RF Parts used to sell these, plus various
    Japanese ones.

    Tam
     
  7. John Larkin

    John Larkin Guest


    Nowadays, there are opamps that will give plenty of low-distortion
    gain to this frequency, or 10x this frequency even. And cheap MMICs
    give numbers like 20 dB gain, 3 dB NF, and DC-5 GHz bandwidth.

    Check TI and Analog Devices for screaming opamps. Sirenza or
    Mini-Circuits for nice MMICs.

    John
     
  8. Fred Bloggs

    Fred Bloggs Guest

    You can't be serious! Maybe at unity gain and signal levels <30dBm...and
    which distortion IP3 or IP2- not aware that THD is used at these
    frequencies- geez wonder why....
     
  9. John Larkin

    John Larkin Guest

    Of course I'm serious. Opamp GBWs are now at 18 GHz, and cheap 50-ohm
    darlington MMICs are up to 10 GHz. But the op's request is pretty
    (well, very) vague, so we don't know what's important here. He did say
    "input stage" so 30 dBm likely isn't called for, unless it's the input
    stage for a big ole transmitter!

    John
     
  10. Reg Edwards

    Reg Edwards Guest

    =====================

    Agreed I'm out of date. But suppose he wants a medium to high input
    impedance, as he is likely to want at 200 MHz.
     
  11. John Larkin

    John Larkin Guest


    An opamp will do that, fraction of a pF. But we don't know what he
    wants.

    John
     
  12. Activ8

    Activ8 Guest

    That's "silver screen".
     
  13. Thoma HauC

    Thoma HauC Guest

    After reading your answers, I realize that I was not very precise. The input
    stage will consist of several scales (1/1, 1/10 & 1/100). It will have to
    present an impedance of 1 Mohms. What interests me, it is the structure in
    order to have a low impedance output in the first stage. If I put a follower,
    it will distort the signal.

    Input impedance : 1 Momhs
    Wide band : 200 MHz
    Low distortion : 80 dB
    Three scales : 1/1, 1/10
    Maximum input voltage : 5 V

    Thank you in advance
     
  14. Thoma HauC

    Thoma HauC Guest

    After reading your answers, I realize that I was not very precise. The input
    stage will consist of several scales (1/1 & 1/10). It will have to
    present an impedance of 1 Mohms. What interests me, it is the structure in
    order to have a low impedance output in the first stage. If I put a follower,
    it will distort the signal.

    Input impedance : 1 Momhs
    Wide band : 200 MHz
    Low distortion : 80 dB
    Three scales : 1/1, 1/10
    Maximum input voltage : 5 V

    Thank you in advance
     
  15. Thoma HauC

    Thoma HauC Guest

    After reading your answers, I realize that I was not very precise. The input
    stage will consist of several scales (1/1 & 1/10). It will have to
    present an impedance of 1 Mohms. What interests me, it is the structure in
    order to have a low impedance output in the first stage. If I put a follower,
    it will distort the signal.

    Input impedance : 1 Momhs
    Wide band : 200 MHz
    Low distortion : 80 dB
    Three scales : 1/1, 1/10
    Maximum input voltage : 5 V

    Thank you in advance

    Thoma
     
  16. Tam/WB2TT

    Tam/WB2TT Guest

    I don't think there is a device in existance that has 1 Megaohm impedance at
    200 MHz, not even a 1M reistor.

    Tam
     
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