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UK practical help with pulse generator

Gordon
 

On 01/04/2016 15:37, Tom Gardner tggzzz@... [TekScopes] wrote:
At 5V and using a 350MHz scope (Tek 485) the risetime/falltime is fractionally
under 1ns. Looking at the spectrum leads me to believe the risetime is
600-650ns.
That's the scope and generator rise summed of course. The 485 is spec'd at 1ns so one, the other or both are faster but that's part of what I'd like to know. If you know one for definite you can calculate the other, within reason. Rightly or wrongly I thought it would be easier to 'tighten up' the layout with a single chip and I wanted something that could be put together by anyone with reasonably predictable results. David Hess pointed me to what I think was the origin of the paralleled 7414 circuit and I did try it but the overshoot/ringing bothered me a bit. OK for the tdr which it was originally designed for I think but not really good enough for calibrating overshoot!

Without calibrating the 485, it looks like
<>

It works down to a supply voltage <1.5V, with correspondingly lower output
voltages and much slower transition times, of course.

In contrast, 3 NC74SZ04 have a marginally slower risetime of about 1ns.
I based my choice on the minimum tpd which is lower for the NC7... assuming the rise time has to support the minimum tpd but I'm not that experienced at these things so we'll see.

Cheers

Gordon
 

On 01/04/16 16:00, 'David C. Partridge' david.partridge@...
[TekScopes] wrote:

Don't you mean "looking at the spectrum leads me to believe that the risetime
is 600-650pS" (i.e. not nS).
Oh..... rats :) And it is too late to claim an All Fools day joke :(

But I definitely don't mean picoSiemens (nor even picoSamples)!

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 01 April 2016 15:38
To: TekScopes@...
Subject: Re: [TekScopes] UK practical help with pulse generator

At 5V and using a 350MHz scope (Tek 485) the risetime/falltime is
fractionally under 1ns. Looking at the spectrum leads me to believe the
risetime is 600-650ns. Without calibrating the 485, it looks like
 

Don't you mean "looking at the spectrum leads me to believe that the risetime is 600-650pS" (i.e. not nS).

Dave

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 01 April 2016 15:38
To: TekScopes@...
Subject: Re: [TekScopes] UK practical help with pulse generator

At 5V and using a 350MHz scope (Tek 485) the risetime/falltime is fractionally under 1ns. Looking at the spectrum leads me to believe the risetime is 600-650ns. Without calibrating the 485, it looks like
------------------------------------
Posted by: Tom Gardner <tggzzz@...>
------------------------------------
 

On 01/04/16 10:24, Gordon tekscopes@... [TekScopes] wrote:
I'm guessing I'm probably not the only group member with a need for a
decent pulse generator. It uses NC7SZ14 chips. 50 Ohms out by the way. Variable from ~0.5V to ~1V.
FWIW, I have something similar based on three parallel (74LVC1G14 + 130ohm). The three parallel outputs lessens the effects of reduced drive strengths as the output approaches the supply rails.

At 5V and using a 350MHz scope (Tek 485) the risetime/falltime is fractionally under 1ns. Looking at the spectrum leads me to believe the risetime is 600-650ns. Without calibrating the 485, it looks like <>

It works down to a supply voltage <1.5V, with correspondingly lower output voltages and much slower transition times, of course.

In contrast, 3 NC74SZ04 have a marginally slower risetime of about 1ns.
 

I'm in Kenilworth, and also have a 7104 and a 7S11 with S6 and 7T11 sampler - also available to assist.

Dave
Gordon
 

On 01/04/2016 10:24, Gordon tekscopes@... [TekScopes] wrote:
I'm hoping someone in the UK can spare the time to give me a little
practical help with a pulse generator.
Thanks to all who offered to help both on and off list. What a great place this is. Craig is giving it a coat of looking at so we'll see how it performs in due course no doubt.

Thanks again

Gordon
 

Gordon,

I'm in Swindon and will happily look at it using my 7104 scope, if
that is going to help.

Regards,

Norman



Hi. I'm hoping someone in the UK can spare the time to give me a little
practical help with a pulse generator. I don't have leveled oscillators,
standardizers etc, and generally only very occasionally need high speed
stuff. 400MHz is 399MHz more than I need most of the time. I have a 7a13
with relay problems, more on that in another post. A decent pulse
generator should give me some indication of any problems with the
replacement relays. I've made one. The problem is I don't know how
decent it is, I just don't have the equipment. I've tweaked the vertical
amp in the 7834 (haven't touched L1667 as I can't mark its original
position easily) - pre tweak
post tweak
which looks like it's
just about in spec but for all I know I could be over compensating for
overshoot in the pulse generator
.

I'm guessing I'm probably not the only group member with a need for a
decent pulse generator. It uses two NC7SZ14 chips. One for the
oscillator which gives a trigger out before the pulse if you need it
(albeit inverted) and one for the output. If someone could test it and
if necessary tweak it I'd package it up and make the files available to
the group, either on here or maybe on OSH. No need to return the
generator. Just measure, tweak if necessary and provide results -
please:) 50 Ohms out by the way. Variable from ~0.5V to ~1V.

Cheers

Gordon
Gordon
 

Hi. I'm hoping someone in the UK can spare the time to give me a little practical help with a pulse generator. I don't have leveled oscillators, standardizers etc, and generally only very occasionally need high speed stuff. 400MHz is 399MHz more than I need most of the time. I have a 7a13 with relay problems, more on that in another post. A decent pulse generator should give me some indication of any problems with the replacement relays. I've made one. The problem is I don't know how decent it is, I just don't have the equipment. I've tweaked the vertical amp in the 7834 (haven't touched L1667 as I can't mark its original position easily) - pre tweak post tweak which looks like it's just about in spec but for all I know I could be over compensating for overshoot in the pulse generator .

I'm guessing I'm probably not the only group member with a need for a decent pulse generator. It uses two NC7SZ14 chips. One for the oscillator which gives a trigger out before the pulse if you need it (albeit inverted) and one for the output. If someone could test it and if necessary tweak it I'd package it up and make the files available to the group, either on here or maybe on OSH. No need to return the generator. Just measure, tweak if necessary and provide results - please:) 50 Ohms out by the way. Variable from ~0.5V to ~1V.

Cheers

Gordon

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