So I finally got the amplifier all measured up, with three different pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143. Joerg's suggestion of bodging in a bypass right at the collector load made the amp stable even with the Avago parts, which are hotter than the Skyworks one. I dremelled down to the ground plane, so the inductance is only 1-2 nH. Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the flatband, and < 1 pF input capacitance. Second stage contribution becomes important above ~100 MHz. See http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html . Measuring all that was interesting--getting decent accuracy for noise levels that small at high frequency is hard. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Stabilizing pHEMTs
Started by ●March 9, 2012
Reply by ●March 21, 20122012-03-21
Reply by ●March 21, 20122012-03-21
On Wed, 21 Mar 2012 10:59:18 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>So I finally got the amplifier all measured up, with three different >pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143. Joerg's >suggestion of bodging in a bypass right at the collector load made the >amp stable even with the Avago parts, which are hotter than the Skyworks >one. I dremelled down to the ground plane, so the inductance is only >1-2 nH. > >Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the >flatband, and < 1 pF input capacitance. Second stage contribution >becomes important above ~100 MHz. See >http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html . > >Measuring all that was interesting--getting decent accuracy for noise >levels that small at high frequency is hard. > >Cheers > >Phil HobbsHi, Phil, Did you ever get the NE3509 to stop screaming? I measured its gate capacitance at about half a pF. -- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●March 21, 20122012-03-21
John Larkin wrote:> > On Wed, 21 Mar 2012 10:59:18 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >So I finally got the amplifier all measured up, with three different > >pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143. Joerg's > >suggestion of bodging in a bypass right at the collector load made the > >amp stable even with the Avago parts, which are hotter than the Skyworks > >one. I dremelled down to the ground plane, so the inductance is only > >1-2 nH. > > > >Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the > >flatband, and < 1 pF input capacitance. Second stage contribution > >becomes important above ~100 MHz. See > >http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html . > > > >Measuring all that was interesting--getting decent accuracy for noise > >levels that small at high frequency is hard. > > > >Cheers > > > >Phil Hobbs > > Hi, Phil, > > Did you ever get the NE3509 to stop screaming? I measured its gate > capacitance at about half a pF. >I'll try that next. Its pinout is different, so it isn't as easy to use in this amp. Cheers Phil -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●March 21, 20122012-03-21
Phil Hobbs wrote:> So I finally got the amplifier all measured up, with three different > pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143. Joerg's > suggestion of bodging in a bypass right at the collector load made the > amp stable even with the Avago parts, which are hotter than the Skyworks > one. I dremelled down to the ground plane, so the inductance is only > 1-2 nH. > > Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the > flatband, and < 1 pF input capacitance. Second stage contribution > becomes important above ~100 MHz. See > http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html . > > Measuring all that was interesting--getting decent accuracy for noise > levels that small at high frequency is hard. >1/f is nearly always horrid with RF parts. If it's true wideband amplification you are after the only way is probably to diplex in a decent LF amp for the stuff under 20MHz. Of course that may not be helping much with phase noise in the GHz range. I have done such splits before in FO gear but I had the luxury of a "dead band" (the client didn't need any signals from inseide there) from a few hundred kHz to a couple MHz or so. Meaning my diplexing could be rather crude. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●March 21, 20122012-03-21
On Wed, 21 Mar 2012 10:01:48 -0700, Joerg <invalid@invalid.invalid> wrote:>Phil Hobbs wrote: >> So I finally got the amplifier all measured up, with three different >> pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143. Joerg's >> suggestion of bodging in a bypass right at the collector load made the >> amp stable even with the Avago parts, which are hotter than the Skyworks >> one. I dremelled down to the ground plane, so the inductance is only >> 1-2 nH. >> >> Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the >> flatband, and < 1 pF input capacitance. Second stage contribution >> becomes important above ~100 MHz. See >> http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html . >> >> Measuring all that was interesting--getting decent accuracy for noise >> levels that small at high frequency is hard. >> > >1/f is nearly always horrid with RF parts. If it's true wideband >amplification you are after the only way is probably to diplex in a >decent LF amp for the stuff under 20MHz. Of course that may not be >helping much with phase noise in the GHz range. > >I have done such splits before in FO gear but I had the luxury of a >"dead band" (the client didn't need any signals from inseide there) from >a few hundred kHz to a couple MHz or so. Meaning my diplexing could be >rather crude.We run into that same issue. The superfast parts, like distributed amps, are inherently AC coupled, so we have to split the signal path and squirt the DC part back in at the very end, with a wideband inductor. If there are multiple places in the fast path that are AC coupled, the DC path gets messy, and it's hard to get flat step response. -- John Larkin, President Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●March 21, 20122012-03-21
Joerg wrote:> > Phil Hobbs wrote: > > So I finally got the amplifier all measured up, with three different > > pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143. Joerg's > > suggestion of bodging in a bypass right at the collector load made the > > amp stable even with the Avago parts, which are hotter than the Skyworks > > one. I dremelled down to the ground plane, so the inductance is only > > 1-2 nH. > > > > Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the > > flatband, and < 1 pF input capacitance. Second stage contribution > > becomes important above ~100 MHz. See > > http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html . > > > > Measuring all that was interesting--getting decent accuracy for noise > > levels that small at high frequency is hard. > > > > 1/f is nearly always horrid with RF parts. If it's true wideband > amplification you are after the only way is probably to diplex in a > decent LF amp for the stuff under 20MHz. Of course that may not be > helping much with phase noise in the GHz range. > > I have done such splits before in FO gear but I had the luxury of a > "dead band" (the client didn't need any signals from inseide there) from > a few hundred kHz to a couple MHz or so. Meaning my diplexing could be > rather crude. > > -- > Regards, Joerg > > http://www.analogconsultants.com/Actually, it's okay for fast bootstraps and some TIAs--the differentiating action of the input capacitance gets rid of most of the low frequency schmutz. It's pretty good medicine for the 1 nA/100 MHz problem, which actually looks like it might be doable. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
