Really triangular triangles

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2 and R2 represent your pad capacitance and input resistance. Then by choos= ing a feedback R1 C1 with identical time constant, the square wave voltages= across R2 and R1 will be =A0equal. It's a way of putting the test waveform= on your circuit input without tapping it with anything less than ultra-hig= h Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want the= re directly, a rectangular waveform.

Your initial post said something about 0.8p input capacitance, now are you = saying 0.3p? You're not going to get much of a step across that with the di= fferentiated triangle. And you keep talking about TCs. How harsh is the typ= ical PCR lab anyway? I would think 15o-30o covers it in the extreme.

When I checked the thread through my Forte account, my Google groups posts weren't there. Here's my response again.

The circuit I posted defined the slope of the 5usec ramp with a constant current derived from a long-tailed pair of BFR92 transistors.

It's going to be very linear. The slope depends on the current through the tail. You've got 5V to play with so we could put a current source in the tail with a precision resistor, and N-FET and an op amp to make it really well defined. The current gain of the BFR92 ranges from a minimum of 65 to the typical 90 up to 135, so you could lose as much as 1.5% of your tail current through the base junction. Bipolar transistor gain rises with temperature, so this proportion would be temperature dependent.

If you want something more stable, it might be worth looking at making the long-tailed pair with two BFRT92/BFR92 complementary Darlingtons; you'd probably need to jack up the current a bit (and increase the timing capacitor in proportion) to keep the lower-current part of the complementary pair tolerably fast.

The 50usec recovery is exponential, with roughly 30uA through R1. You could make it a constant current source - in the good old days you could buy selected FETs for use as constant current diodes, but today it looks as if you'd have to buy a Fairchild J201 and put a resistor between source and gate.

About 30k would get you of the order of 30uA with a "typical" gate-to- source cut-off voltage, but you'd have to do select on test to get anything reliable or usefully predictable.

A PNP current mirror would be easier, but - as usual - you have to worry about the base current and the Early effect.

You could use a P-channel FET and a rail-to-rail op amp to set up precise current source. Farnell stock the MMBFJ177 which looks as if it could be made to work

How much you'd have to do to get the degree of predictablity and flatness that you need rather depends on what numbers you want to attach to "predictable", "flat" and "temperature independent". There are well know solutions for every level of accuracy - as you raise your standards, the components become more numerous and expensive.

E-mail me if you don't want to be explicit in public.

--
Bill Sloman, Nijmegen

and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Do the math. All I need is 10 nA, which I get with 200 kV/s into 0.05 pF coupling capacitance. The 0.3 pF is a wish, 0.8 is what I expect to get. But even another 0.1 pF is 1 dB of SNR degradation, so since I need a shield anyway, I'm going to use that.

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

as I unsersand it he wants to feed the triangle wave through a capacitor into a resistor to generate the calibration vaveform

--
?? 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net

and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Looks like you may not want to use FR4 for this. Maybe Rogers 5000 or Teflon?

--
Regards, Joerg

http://www.analogconsultants.com/

and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Something with a low epsilon would make sense, for sure. My test board has a ground plane cutout about 200 mils square under the gate node, but using something with epsilon = 2.2 instead of 4.6ish would be a win.

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

and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Usually the pads on small parts are so tiny that pad capacitance is much less than device capacitance. But of course you can do the math. Ground cutouts help, especially if ground is layer 2 of a multilayer.

Oh, our EM sims and ground cutouts seem to have worked pretty well on the edge-launch SMAs. Here's our output pulse:

That's the 10/90 rise and fall time. For some reason, people in the fast pulse biz like to use 20/80 rise time in their specs, and sometimes actually admit it. If I do that, I get...

42 picosecond rise and fall! That was done with a 40 GHz sampling scope and essentially zero cable between the pulser and the sampling head. Just a few inches of coax trash the risetime at these speeds. The SMAs have to be carefully torqued, too.

--

John Larkin                  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

comparator

wave

You

but

at

exactly

in a

as

pF

packaged

The

an

attenuation,

waves

C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Very pretty. Another factor of 2 and you'd be in SD-24 territory.

BTW I get occasional low-frequency mis-triggering on the rising edge of TDR pulses in my 11802, so that there's sometimes a lump of junk out ~50 ps in front of the rising edge. Happens on two different SD-24s. Nothing too serious at the moment, as long as it doesn't deteriorate rapidly.

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

comparator

wave

You

but

high

at

Same

exactly

trick,

in a

as

1 pF

packaged

add

coupling

The

a

be an

attenuation,

waves

C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

I haven't noticed that. I'll look.

You can see a famous SD24 bug: the TDR step time shifts some picoseconds back and forth in sync with the blinking "TDR" led.

--

John Larkin                  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

Tim

comparator

triangular wave

MC100EP116.

You

ramps, but

high

pulses at

pretty

and

compensation

Same

exactly

happen.

unusual

noise

trick,

(Easy in a

works as

under 1 pF

packaged

add

coupling

anyway.) The

of a

be an

attenuation,

waves

feedback. C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

which is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

Otherwise

are you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

If that were my only timing problem, I'd be a lot better off than I am now.

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

I am in the process of repairing a Tektronix 11802 that I got on ebay recently. Most of the issues have been resolved by replacing NVRAM batteries.

However, I think there might be one EPROM having issues. Would one or more of you that own the 11802 possibly make binaries from the eproms? If the Executive and Time base controller have Version 10.xx firmware or greater, that would really be a plus.

If you have the 11801 and need the firmware => 10.xx, I can help.

The firmware is in a total of 20 27C512 EPROMS so it will take some time to copy them. These EPROMS dont last forever so having a backup may save you a future problem.

Regards

comparator

wave

You

but

at

exactly

in a

as

pF

packaged

The

an

attenuation,

waves

C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

That could possibly be solved by one swift motion with the wire cutters ... snip :-)

--
Regards, Joerg

http://www.analogconsultants.com/

and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Might be a bit hot, but instead of a GND plane you could bootstrap the parasitics and have a small buffered copper area on layer 2 under the gate node.

--
Thanks,
Fred.

comparator

wave

but

a

pF

The

an

attenuation,

C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Bootstrapping doesn't help in this instance--I'm letting the gate node have whatever TC it wants, and fixing it up afterwards by differentiating. Trying to do few-electron things in a built-up circuit requires a certain chastity of outlook. ;)

I need the shield on top anyway, because otherwise this thing is going to see stray capacitance from passing airplanes.

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

comparator

wave

You

but

high

at

Same

exactly

trick,

in a

as

1 pF

packaged

add

coupling

The

a

be an

attenuation,

waves

C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

I'll have to look into that one of these days. Older LEDs used a lot of current. Maybe a newer LED and a bigger resistor would fix it. Or maybe it's not the LED current at all.

It is surprising that Tek apparently never fixed it.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Tim

comparator

wave

MC100EP116.

You

ramps, but

high

pulses at

and

compensation

Same

exactly

happen.

trick,

in a

works as

1 pF

packaged

add

coupling

The

of a

be an

attenuation,

waves

feedback. C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

Or that they possibly didn't follow one of the cardinal rules in low-jitter designs: Never, ever, have a load change. Anywhere.

One debug session where I finally found the noise source was a RAM board, in the days when this stuff was very power-hungry, toasty and big. They were loading RAM banks ping-pong style but the duty cycle for each was less than 50%. Meaning there were gaps where the whole circuit sudenly drew much less current. The fix was to fill that up, I don't remember whether we stretched the load clock or just let some dummy process fill the gap but afterwards the noise was gone.

--
Regards, Joerg

http://www.analogconsultants.com/

Tim

comparator

triangular wave

MC100EP116.

You

ramps, but

high

pulses at

pretty

and

compensation

Same

exactly

happen.

unusual

noise

trick,

(Easy in a

works as

under 1 pF

packaged

add

coupling

anyway.) The

of a

be an

attenuation,

waves

feedback. C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

which is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

Otherwise

are you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

OK, I'll reveal one of my Great Secrets: the key to picosecond-jitter circuitry is often the low frequency stuff: power supplies, DAC noise, ground loops, 1/f, thermals.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Tim

comparator

triangular wave

MC100EP116.

allow. You

ramps, but

high

pulses at

pretty

and

compensation

Same

exactly

happen.

unusual

noise

trick,

5-1/2

(Easy in a

works as

under 1 pF

packaged

to add

coupling

anyway.) The

of a

could be an

attenuation,

waves

feedback. C2 and R2 represent your pad capacitance and input resistance. Then by choosing a feedback R1 C1 with identical time constant, the square wave voltages across R2 and R1 will be equal. It's a way of putting the test waveform on your circuit input without tapping it with anything less than ultra-high Z at your frequencies of interest.

which is just an approximation anyway, when you can put the end result you want there directly, a rectangular waveform.

Otherwise

are you saying 0.3p? You're not going to get much of a step across that with the differentiated triangle. And you keep talking about TCs. How harsh is the typical PCR lab anyway? I would think 15o-30o covers it in the extreme.

to

You forgot two: Beer, and Sutro Tower :-)

--
Regards, Joerg

http://www.analogconsultants.com/

mostly

basic

a

Early

32, and

series

otherwise

resistor to

to

gets

again.

reasonably

means

frequency

those

production

three

right--just

anything

pad

that

which is

(ideally

the

or

fast

almost

to

folks to

per

its

big

capacitances

that.

so it

smart

their

blew

souped-up

And you don't hear the meat grinder starting?

?-)