Ideally one could use one of those monolithic multi-transistors on a single die, like the CA3096...it doesn't seem like you can get 'em for any reasonable price anymore, though. They have them direct from China on eBay. I'm a little leery of that option...burned before!
I also had an idea for a faster variation on the LM13700 OTA using a couple transistor array ICs and a Burr Brown current source/mirror chip. It would "only" cost 15 bucks...:(
No, I've never really designed or worked with analog video amps/RF modulators/NTSC etc.
I'm in my 30s, for most of my adult life "video" means "you plug in the magic (digital) cable and it works." I only know the terms and a little bit about that technology, like 8 track players and vacuum-tube computers, from what you might call "books of historical interest" ;-)
I've been doing picosecond stuff too. 16,666,666,666 ps, unfortunately.
It's a little different than a usual op-amp topology - at low frequencies the LTP and mirror are driving the emitter followers through Q6 and Q7, and high frequencies they're bypassed by C1 and C2 to put current directly into the output transistor bases. I think it's trading off open-loop gain at high frequencies for lower overall phase shift and higher slew rate.
When we get around to doing a next gen, I'll send you one. The P400 works fine, but it is sort of ugly.
A DDG is a wonderful thing to have around, a real Time Machine.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
That's an amazing part, 0.3 nv/rthz at 5 mA. As you say, you can't put anything in series with the gate without adding Johnson noise.
Four of them is (calculates furiously) 0.15 nv/rthz!
Are the fets hard in parallel? Maybe they could run separately, and sum downstream. I just designed an amp that has two independent gain paths, resistively summed at the very output.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
No, the polarities are wrong for C1 and C2 to be forward gain paths.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Am 17.05.2017 um 04:26 schrieb Ralph Barone:
Yeah, lots of them!
If you want a complete model, just crank the CM impedance up to a reasonable value. 150 ohms is ballpark typical of UTP in raceways, intermingling with other cables.
This is why they terminate the cable-facing windings with resistors to ground. (Except it's not really ground, it's ESD-sinking-ground, with a 1nF
1.5kV cap. And, guess what an 8kV contact ESD hit divides down to, when connected to 1nF? Right, around 1.5kV -- the system works, and that's where the isolation spec comes from.)Ethernet transformers are largely rated for 30dB of anything (CMRR, balance, isolation). They're hardly perfect*, so the CMC on the outside definitely helps, even if it isn't terminated into much.
*The 30dB specs look more like conforming to the standard, than measured characteristics of anyone's actual product. Like a JEDEC 2N2222 spec, you might get something that skirts the standard, or you might get something a whole lot better... who knows.Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Yeah, it wouldn't work so well without current gain from the mirrors; that's just R+C compensation, which gives about a decade past the dominant-pole compensation that is traditional, which is just dumb, really.
It's compensated for unity gain stability, and yes, it is a proper op-amp block, with uncommitted inputs and crappy saturation near the rails (for inputs and outputs). :) If you need more GBW and less feedback, just crank the compensation values down.
I wouldn't think it would be very useful into the 100s of MHz, because of real delays in a practical circuit. The emitter degeneration helps, but global feedback can only do so much.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
It gives me more time to think over what I'm doing :-)
I used to joke that to the relaying people anything over 60 Hz was RF, and that to the telecom people, anything under 10.7 MHz was DC.
To optical antenna people, DC goes up to 1 THz. ;)
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 hobbs at electrooptical dot net http://electrooptical.net
But slowly varying DC.
-- Reinhardt
I reviewed my old archives. It turns out I used the HP 5326 in 1971. This could reach 100ps using Time Interval Averaging, which was excellent for the time.
HP released the 5370 around 1978. This could reach 20ps single shot and
63 fs using 1e5 averaging. This took too long in production, so I settled on 1e4 averaging. This gave 200 fs which was 500x better than the original.It is clear that by the early 1980's, many people were involved in picosecond and femtosecond design and measurements.
Yah. But not you, in 1970.
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 hobbs at electrooptical dot net http://electrooptical.net
To the contrary, this thread has illustrated that LTspice drawings can be utterly useless. One can make a SPICE model do almost anything apparently, and reality has little to do with it. In contrast, a hand-drawn schematic, depending on who has drawn it, is more likely to have knowledgeable analytical analysis behind it, and therefore be believable and eminently useful.
--
Thanks,
- Win
Bah, you guys are fooling around with 50 to 300MHz parts, go play with Intersil's serious monolithic BJTs: HFA3096, HFA3127, HFA3128, HFA3046, HFA3101, HFA3102, etc. These have fT ratings up to 10GHz. HFA3134 and HFA3135, nice!
--
Thanks,
- Win
I keep trying to use those for something cool, and somehow they never quite fit.
Disappointing Ree' and beta linearity, mostly. Also V_A is only about 15V.
Now if I could get monolithic dual BFP640s, _that_ would be cool.
My latest gizmo uses a couple of those wrapped round each side of a MAT14 d iff pair. It's a biased Darlington stage to return the base current to the collector to extend the effective f_T of the MAT14, and a common emitter st age looking at the MAT14's base and driving the Darlington's base to keep i t still.
In the spherical-cow universe that extends the MAT14's f_T by about an orde r of magnitude while keeping its other nice properties.
We'll see how it works in a week or two.
Cheers
Phil
OK, actually, I haven't found many useful applications either. Their operating current ratings are rather low.
--
Thanks,
- Win
They were real fun in a time stretcher, that ft combined with the fat space qualified ceramic flatpack with looong leads. But they are about the only qualified RF PNPs that are left.
Gerhard
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