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
Looking for fast-ish sot-89 NPN
Started by ●May 9, 2022
Reply by ●May 9, 20222022-05-09
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, GerhardSOT-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
Reply by ●May 10, 20222022-05-10
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
Reply by ●May 11, 20222022-05-11
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, KE5FXI 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
Reply by ●May 11, 20222022-05-11
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, GerhardIf 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
Reply by ●May 12, 20222022-05-12
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, GerhardI wonder if some SOT89 transmitter Fet would work. Some are stable from here to there, and fast too. AFT something
Reply by ●May 13, 20222022-05-13
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
Reply by ●May 13, 20222022-05-13
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
