Looking for fast-ish sot-89 NPN...

  • Thread starter Gerhard Hoffmann
  • Start date
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Gerhard Hoffmann

Guest
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
 
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
Click to expand...

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
 
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.
Click to expand...

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
 
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
Click to expand...

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
 
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
Click to expand...

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

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
 
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.
Click to expand...

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
 
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