linear ramp

I'm not seeing the problem. An integrator (resistor, capacitor, inverting voltage-gain element) on a square pulse (CMOS is fast and easy to power with a reference voltage) only needs a transistor.

See my example circuit,

The transistor speed relates to the Miller capacitance; you can swamp that (200 pF in your ramp capacitor), and the thermal fluctuations are even lower. No nonlinearity there.

The transistor voltage gain is high; with collector voltage going from

2V to 5V, and a +15 supply, the collector current is changing thirty percent; that corresponds to Vbe change of 6 millivolts, and you'd start with 3 to 5V drive. This is well under your 1% requirement, and with some trickery to raise the pullup's impedance (current source in parallel, or ferrite bead) you can add another order of magnitude. No nonlinearity problem.

Base current? It's only a few dozen microamps, and doesn't change in 30 ns due to any thermal drifts. Output is AC-coupled, notice; just has to pass fast ramps, not thermal dreck.

So, I'm not seeing any problem that requires ultrafast chips from the op amp suppliers. Am I missing something?

Right. The chrome plated variety are too much hassle to clean and they rust to bits in a couple of years. Anything that's going to be out in the rain and all weathers should be stainless.

There's the old joke about farmers, leaving the combine out in the corner of a field till next year once the work is done and then surprised when it no longer works :-). Must have been the old days though, before the rise of contracting...

Regards,

Chris

My present unit is two years old now, no problems. Previous unit had cast iron burners. During the winter a field rat got inside it and made a royal mess, and all the innards rusted together :-( I couldn't disassemble it, so I took a cut-off saw to it ;-)

Of course, in the 15 years since I did the first install, units of this grade became stainless and HEAVY, so my project required much re-work and a lift table to install...

I no longer have field rat problems... I have natural exterminators now...

My grandfather Godwin used a Belgian work horse about the size of a Clydesdale ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

Looks like the sort of creative solution that you used to see in old discreet component tek scope and test gear schematics.

Any fool can get results using exotic parts. Takes an engineer to make it work to spec using cheap vanilla parts :-)...

Regards,

Chris

Sigh... Here we go again. Isn't it possible to be critical without losing it completely and throwing all the toys out of the cot ?.

If you have such sensitive buttons, it's no surprise if some people push them just for the amusement of it all :-)...

Regards,

Chris

Can't that be compensated elsewhere ?. As for base current, haven't worked it out, but looks like it may be insignificant in relation to the

1k charging line current.

Which the diode isolates, yes ?.

Regards,

Chris

Worked on a project that used hundreds of lvds serdes devices for board to board comms, using screened RJ45 connectors and cables. Forget the part number, but it was a ti device with 800Mhz internal clock rate. We were running at around 100 Mhz data rate and the 100 Mhz harmonics from the lvds were all that could be seen on the s/a right up to over 1Ghz. Nearly failed it's approval tests until we put fingers on all the access doors.

Would try to avoid in the future, though would add that I wasn't, thankfully, responsible for that part of the h/w design...

Regards,

Chris

I presume the un-attributed quotations are from Larkin?

Figures. He can take my comments about BU and turn them into "insulting" his wife. He's a village idiot. He tries to be an asshole, but he's not competent.

I do have a major personality fault... I'm totally intolerant of ignorance, and I get my jolly's by pushing their buttons... the more they incoherently react, the more I push... I do derive amusement... Schadenfreude :-)

Find me a tolerable circuit that Larkin has posted. They're trash at best.

And Slowman can't even fire up a 555 Timer.

'Nuff said.

(They both are, BTW, kill-filed. I only comment on their posts when someone else chooses to troll-feed them and I see it.) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

That's quite puzzling. I did a driver/receiver chip design for Fairchild (at 1GB) and it was as quiet as a church mouse. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

Aha! I just remembered that some quasi-LVDS aren't really current-mode, but pulsed current to save average power. True current mode is quiet (if loads are really balanced). ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

They were clear, direct, personal, and repeated insults aimed my wife.

Hence "asshole."

He's a village idiot. He tries to be an

Sure sounds like an asshole to me.

John

Sure, for more parts. Opamps take care of this sort of thing.

As for base current, haven't

The LVDS receiver is actually being used as a comparator.

No.

John

OK, who "all" here is amused by Thompson insulting my wife?

Who here has a wife and doesn't care if she is insulted?

Who here thinks Thompson is an asshole for doing this here, and thinking he's clever for doing it?

I sure do.

John

I'm not taking sides, just found it amusing that a couple of line post could provoke such vitriolic outburst of 4 post invective, for what seemed like no reason at all. Balloons are sometimes there to be pricked, in any case.

Can't say about the wife, as I haven't seen the posts in question. Mine would be more than capable of dealing with insult, having worked in the uk educations system, in inclusion units for difficult kids, for around ten years.

So, lighten up a bit. Life's too short to bear grudges. Talk tech instead. You are much better at that :-)...

Regards,

Chris

I've made the suggestion in the past that John and Jim need to be locked into the same room for a bit, have their knock-down drag-out fight, and afterwards they'll be best of friends. :-)

Ok, don't know enough about the application, but if you are using the single ramp to drive >1 section, can't you arrange for the drift to cancel out over the sections ?.

Once the driver switches off, there's only the diode cap remaining ?.

Dunno, just seems like an expensive solution. I know time is money, but it is only a simple ramp and it would be an interesting challenge to see how few low cost parts could be made to do the job and still meet spec...

Regards,

Chris

Larkin is manic-depressive... no chance.

Larkin is really good at BS.

History: Larkin mentioned that his wife went to BU. I opined (FACTUALLY) that the frat houses on the MIT (Memorial Drive) side of the Charles River featured darkened rooms with telescopes. And the BU girls (dorms on the Storrow Drive side of the river) were fond of undressing at their dorm windows.

Larkin went ballistic. Conclusion: Larkin is a village idiot ;-)

Larkin also claimed his wife worked at restaurants and laughed at the MIT geeks. Asked for restaurant names, Larkin gave no response.

I think he made the whole story up. He should hook up with Slowman. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

How could I be friends with a dead guy ?:-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

He has offered to "be best of friends", presumably if I start behaving more like him. I guess that means I should insult his wife, too.

No thanks.

And I wouldn't be willing to get physical with a crippled senile ancient.

John