• Looking for fast-ish sot-89 NPN

    From Gerhard Hoffmann@21:1/5 to All on Tue May 10 00:27:53 2022
    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    The circuit is a voltage to current converter, followed by a
    double cascode.

    2N3904 is too slow, BFQ19S is too hot, it would do 1 GHz,
    but brings me negative input impedance, gain peaks and so on.
    I'm playing with the usual ferrite beads, but that does not
    bring complete relief.

    The emitter node of the v/i converter definitely wants to play
    a capacitively loaded follower. I'm just making GND cutouts
    in the layers under the emitter.

    Is there a transistor abt. halfway in speed?
    BFU590 etc is even faster.
    Something flat like SOT-89 would be fine.
    And I would not object 1 GHz BW if it comes without the side effects. :-)

    Any ideas?

    Cheers, Gerhard

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to All on Mon May 9 19:49:55 2022
    On Tue, 10 May 2022 00:27:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
    wrote:

    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    The circuit is a voltage to current converter, followed by a
    double cascode.

    2N3904 is too slow, BFQ19S is too hot, it would do 1 GHz,
    but brings me negative input impedance, gain peaks and so on.
    I'm playing with the usual ferrite beads, but that does not
    bring complete relief.

    The emitter node of the v/i converter definitely wants to play
    a capacitively loaded follower. I'm just making GND cutouts
    in the layers under the emitter.

    Is there a transistor abt. halfway in speed?
    BFU590 etc is even faster.
    Something flat like SOT-89 would be fine.
    And I would not object 1 GHz BW if it comes without the side effects. :-)

    Any ideas?

    Cheers, Gerhard

    SOT-89s seem to be going out of style.

    There are opamps that might do the whole thing for you. One of the THS
    gadgets maybe. THS3091? TI makes some radical fast opamps.







    --

    Anybody can count to one.

    - Robert Widlar

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  • From John Miles, KE5FX@21:1/5 to Gerhard Hoffmann on Tue May 10 15:28:34 2022
    On Monday, May 9, 2022 at 3:28:01 PM UTC-7, Gerhard Hoffmann wrote:
    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    Depending on power/noise requirements, THS3491 is a good way to go for
    200 MHz and below. You can get +20 dBm out of it at 200 MHz, even after
    losing 6 dB in a 50-ohm series termination.

    -- john, KE5FX

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  • From Gerhard Hoffmann@21:1/5 to All on Wed May 11 06:47:01 2022
    Am 11.05.22 um 00:28 schrieb John Miles, KE5FX:
    On Monday, May 9, 2022 at 3:28:01 PM UTC-7, Gerhard Hoffmann wrote:
    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    Depending on power/noise requirements, THS3491 is a good way to go for
    200 MHz and below. You can get +20 dBm out of it at 200 MHz, even after losing 6 dB in a 50-ohm series termination.

    -- john, KE5FX

    I remember when it came out I proposed it on Time Nuts under
    the name "LMH6702 on steroids" and IIRC it did not find much
    enthusiasm.

    This here is more a leisure time project, to convert a former
    NIST-like design by un-PNP-ing it and getting along with 12V Vcc
    without resorting to folded cascodes.

    S22 is already quite OK, but gain == S21 has an unwanted peak
    that comes from the V/I converter. It is dangerous to
    stability. I can reduce it to 5 dB with a damping resistor in
    parallel to one of the beads, but this is experimental voodoo.

    <
    https://www.flickr.com/photos/137684711@N07/52064373427/in/dateposted-public/
    >

    I could use more ferrite on the input, but at frequencies
    where the beads create resistance, they also create thermal
    noise.

    Cheers, Gerhard

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to All on Wed May 11 07:05:53 2022
    On Tue, 10 May 2022 00:27:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
    wrote:

    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    The circuit is a voltage to current converter, followed by a
    double cascode.

    2N3904 is too slow, BFQ19S is too hot, it would do 1 GHz,
    but brings me negative input impedance, gain peaks and so on.
    I'm playing with the usual ferrite beads, but that does not
    bring complete relief.

    The emitter node of the v/i converter definitely wants to play
    a capacitively loaded follower. I'm just making GND cutouts
    in the layers under the emitter.

    Is there a transistor abt. halfway in speed?
    BFU590 etc is even faster.
    Something flat like SOT-89 would be fine.
    And I would not object 1 GHz BW if it comes without the side effects. :-)

    Any ideas?

    Cheers, Gerhard

    If you don't need a lot of swing, use a cheap MMIC.

    Here's a signal pickoff amp with very high reverse isolation. Big
    passive attenuator, then lots of gain.

    https://www.dropbox.com/s/dbekbobus1k8by3/T503_Mon_Pickoff.jpg?dl=0

    That opamp has a fixed gain of 5 and 2.4 GHz bw. There's a version
    with g=10 and 1.8 GHz.



    --

    Anybody can count to one.

    - Robert Widlar

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From LM@21:1/5 to All on Fri May 13 01:02:08 2022
    On Tue, 10 May 2022 00:27:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
    wrote:

    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    The circuit is a voltage to current converter, followed by a
    double cascode.

    2N3904 is too slow, BFQ19S is too hot, it would do 1 GHz,
    but brings me negative input impedance, gain peaks and so on.
    I'm playing with the usual ferrite beads, but that does not
    bring complete relief.

    The emitter node of the v/i converter definitely wants to play
    a capacitively loaded follower. I'm just making GND cutouts
    in the layers under the emitter.

    Is there a transistor abt. halfway in speed?
    BFU590 etc is even faster.
    Something flat like SOT-89 would be fine.
    And I would not object 1 GHz BW if it comes without the side effects. :-)

    Any ideas?

    Cheers, Gerhard
    I wonder if some SOT89 transmitter Fet would work. Some are stable
    from here to there, and fast too. AFT something

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  • From Gerhard Hoffmann@21:1/5 to All on Fri May 13 05:00:05 2022
    Am 11.05.22 um 16:05 schrieb jlarkin@highlandsniptechnology.com:
    On Tue, 10 May 2022 00:27:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
    wrote:

    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    The circuit is a voltage to current converter, followed by a
    double cascode.

    2N3904 is too slow, BFQ19S is too hot, it would do 1 GHz,
    but brings me negative input impedance, gain peaks and so on.
    I'm playing with the usual ferrite beads, but that does not
    bring complete relief.

    The emitter node of the v/i converter definitely wants to play
    a capacitively loaded follower. I'm just making GND cutouts
    in the layers under the emitter.

    Is there a transistor abt. halfway in speed?
    BFU590 etc is even faster.
    Something flat like SOT-89 would be fine.
    And I would not object 1 GHz BW if it comes without the side effects. :-) >>
    Any ideas?

    Cheers, Gerhard

    If you don't need a lot of swing, use a cheap MMIC.

    Here's a signal pickoff amp with very high reverse isolation. Big
    passive attenuator, then lots of gain.

    https://www.dropbox.com/s/dbekbobus1k8by3/T503_Mon_Pickoff.jpg?dl=0

    That opamp has a fixed gain of 5 and 2.4 GHz bw. There's a version
    with g=10 and 1.8 GHz.

    When I want to measure phase noise at -170 dBc @ 100 MHz
    with cross correlation and tricks, then I cannot start with an
    attenuator that puts everything into thermal noise.

    On the output of my PLL it's different. At 10 GHz, it's not
    that hard. You don't need to swimm faster than the sharc, it's
    enough to swimm faster than the guy next to you. Ie, the
    dynamic range is already pretty much reduced and worse
    oscillators in absolute terms will do for the stereo downmixing
    to the cross correlation thing.

    I just want to see the best my crystal oscillators can do @ ~100MHz.

    Cheers, Gerhard

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to All on Fri May 13 09:34:29 2022
    On Fri, 13 May 2022 05:00:05 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
    wrote:

    Am 11.05.22 um 16:05 schrieb jlarkin@highlandsniptechnology.com:
    On Tue, 10 May 2022 00:27:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
    wrote:

    Hi,

    I'm trying to build a 2-200 MHz isolation amplifier.

    For 13 dBm I need abt. 120 mA peak current, 70 mA quiescent.

    The circuit is a voltage to current converter, followed by a
    double cascode.

    2N3904 is too slow, BFQ19S is too hot, it would do 1 GHz,
    but brings me negative input impedance, gain peaks and so on.
    I'm playing with the usual ferrite beads, but that does not
    bring complete relief.

    The emitter node of the v/i converter definitely wants to play
    a capacitively loaded follower. I'm just making GND cutouts
    in the layers under the emitter.

    Is there a transistor abt. halfway in speed?
    BFU590 etc is even faster.
    Something flat like SOT-89 would be fine.
    And I would not object 1 GHz BW if it comes without the side effects. :-) >>>
    Any ideas?

    Cheers, Gerhard

    If you don't need a lot of swing, use a cheap MMIC.

    Here's a signal pickoff amp with very high reverse isolation. Big
    passive attenuator, then lots of gain.

    https://www.dropbox.com/s/dbekbobus1k8by3/T503_Mon_Pickoff.jpg?dl=0

    That opamp has a fixed gain of 5 and 2.4 GHz bw. There's a version
    with g=10 and 1.8 GHz.

    When I want to measure phase noise at -170 dBc @ 100 MHz
    with cross correlation and tricks, then I cannot start with an
    attenuator that puts everything into thermal noise.

    OK. I have 6.5 volts of signal driving an e/o modulator. The pickoff
    is just for a front-panel scope monitor.



    --

    Anybody can count to one.

    - Robert Widlar

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)