[time-nuts] 50 ohm driver

Graham / KE9H ke9h.graham at gmail.com
Sat Mar 7 11:10:45 EST 2015


The question is not the frequency, but the edge rate.  For a 1 PPS signal,
how fast a rise time do you need?  Do you want to know the time of the
edge to 1/100 second? one microsecond? one nano-second? A few pico-seconds?

If you want to know the time of the edge to one nano-second, then you
need a driver that can push sine-waves at over a few GHz. Not 10 MHz.

--- Graham / KE9H

==

On Sat, Mar 7, 2015 at 7:58 AM, Didier Juges <shalimr9 at gmail.com> wrote:

> Martyn, if you only need 1Hz, I recommend you use a MOSFET driver like the
> MIC4420 series or the UCC27531, powered from 10V with a 50 ohm output
> resistance. These parts have several A current capability, 18V or more max
> VCC and are designed to drive capacitive loads (large MOSFET gate
> capacitance). It would not work at 10MHz (because of propagation delay and
> self heating), but at lower frequencies, they work very well.
> The UCC27531 has lower propagation time and comes in an SOT-23 package, the
> others are available in DIP-8 and SO-8.
>
> Didier KO4BB
>
> On Thu, Mar 5, 2015 at 3:59 PM, Martyn Smith <martyn at ptsyst.com> wrote:
>
> > Hello,
> > Thanks for all the feedback.
> > I should explain.  I have an existing product that uses the 74AC14.
> > I have a customer who needs 5V into 50 ohm and can’t wait for the
> > competitive product that does this, or for me to re-design my unit.
> > So I have been looking for a quick fix.
> > I got excited when I found the SN74AS1004AD which has the exact same
> > function and pin out but delivers 48 mA per channel.
> > While one output did give me 0-3.0 V into 50 ohm, combining them, as we
> do
> > for the 74AC, actually produced worse results.
> > Maybe the output driver is different.
> > Anyway I’ve managed to get 0-4.8V by jacking up the supply voltage to 5.7
> > V for the 74AC14 and making the three 47 ohm resistors 0 ohm.
> > Risetime < 4 ns.
> > Basically to ideas that TimeNuts gave me.
> > I’m just worried the IC may die after a few months.  But since the
> > customer will only use it at 1 Hz and hopefully 50:50 duty, or less, I
> hope
> > to get away with it.
> > Of course if he removes the input and the outputs are on high, then that
> > may be a problem.
> > BTW, the reason he wants this high voltage is because he is driving a
> very
> > long cable from the distribution  amp to the actual receiver.
> > Anyway I have an IC on test for a week to make sure it lasts.
> > Regards
> > Martyn
> >
> >
> > Today's Topics:
> >
> >    1. Re: 50 ohm Driver (Bob Albert)
> >    2. Re: 50 ohm Driver (Graham / KE9H)
> >    3. Re: 50 ohm Driver (Tom Van Baak)
> >    4. Re: 50 ohm Driver (Hal Murray)
> >    5. Re: 50 ohm Driver (Dan Kemppainen)
> >    6. Re: Trimble Thunderbolt NMEA ? (Didier Juges)
> >    7. Re: 50 ohm Driver (Bob Camp)
> >    8. Re: 50 ohm Driver (Charles Steinmetz)
> >    9. Re: new tdc from Texas (Angus)
> >   10. Re: new tdc from Texas (Attila Kinali)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Wed, 4 Mar 2015 16:49:11 +0000 (UTC)
> > From: Bob Albert <bob91343 at yahoo.com>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID:
> > <1276775018.2671439.1425487751520.JavaMail.yahoo at mail.yahoo.com>
> > Content-Type: text/plain; charset=UTF-8
> >
> > 5V into 50 Ohms means 100 mA.  Perhaps you need a medium power transistor
> > amplifier or opamp.
> > Bob
> >
> >
> >      On Wednesday, March 4, 2015 6:09 AM, Martyn Smith <
> martyn at ptsyst.com>
> > wrote:
> >
> >
> > Hello,
> >
> > A quick question.
> >
> > My output driver for a simple amplifier.
> >
> > I use three gates (in parallel with resistors) from a 74AC14 to give me
> > about 0-3.2V into 50 ohm.
> >
> > I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing
> > into 50 ohms.
> >
> > Can anyone recommend an IC that can delivery this.
> >
> > But it needs to have similar jitter performance to the 74AC14.
> >
> > I use it up to 10 MHz.
> >
> > Best Regards
> >
> > Martyn
> >
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> >
> >
> >
> > ------------------------------
> >
> > Message: 2
> > Date: Wed, 4 Mar 2015 12:16:02 -0600
> > From: "Graham / KE9H" <ke9h.graham at gmail.com>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID:
> > <CAPyJ-YXrLKw6Y-PogLqWjSS+MEHm6iFc+etyB-mccZkhJPWOQg at mail.gmail.com>
> > Content-Type: text/plain; charset=UTF-8
> >
> > Building on top of John's comments, if you are using a logic gate, look
> at
> > the
> > maximum output (pull up) current per pin, set the series resistor so that
> > this
> > current is not exceeded into a short, then also see if there is a maximum
> > total
> > current draw for all gates combined, or some power input pin, and do not
> > exceed
> > that.
> >
> > You can also look at switching the termination resistor from a simple 50
> > Ohm
> > resistor to ground, to a "Thevenin" load, which is 100 Ohms from +V to
> the
> > load point,
> > and another 100 Ohm resistor from the load point to ground. This way you
> > still have a 50 Ohm termination, but only draw one half the DC current.
> > In the event of no input, the receiver voltage will go to half scale.
> Make
> > sure your system will not misbehave when this happens.
> >
> > Alternate driver is to use a video line driver with sufficient bandwidth.
> >
> > --- Graham / KE9H
> >
> > ==
> >
> > On Wed, Mar 4, 2015 at 7:54 AM, John Ackermann N8UR <jra at febo.com>
> wrote:
> >
> > > One comment on the parallel AC gate approach.  It may not be directly
> > > applicable to Martyn's issue, but there is a common confusion about the
> > > value of the summing resistors.
> > >
> > > Per Tom Clark, who came up with the idea, they are *not* intended to
> > > provide a near-end line termination to 50 ohms, but are simply there to
> > > protect the paralleled devices if the gates have slightly different
> > delays
> > > (in which case one gate could end up sinking the other two).
> > >
> > > So, the commonly used 47 ohm value isn't magic.  You can use a lower
> > > value, and thus get more voltage at the far end.  I haven't
> experimented
> > to
> > > see how far you can take that idea before destroying gates.
> > >
> > > John
> > > ----
> > >
> > > On 3/4/2015 5:26 AM, Martyn Smith wrote:
> > >
> > >> Hello,
> > >>
> > >> A quick question.
> > >>
> > >> My output driver for a simple amplifier.
> > >>
> > >> I use three gates (in parallel with resistors) from a 74AC14 to give
> me
> > >> about 0-3.2V into 50 ohm.
> > >>
> > >> I want to have a driver that gives me a full 0-5V (at least 0-4.5V)
> > swing
> > >> into 50 ohms.
> > >>
> > >> Can anyone recommend an IC that can delivery this.
> > >>
> > >> But it needs to have similar jitter performance to the 74AC14.
> > >>
> > >> I use it up to 10 MHz.
> > >>
> > >> Best Regards
> > >>
> > >> Martyn
> > >>
> > >> _______________________________________________
> > >> time-nuts mailing list -- time-nuts at febo.com
> > >> To unsubscribe, go to https://www.febo.com/cgi-bin/
> > >> mailman/listinfo/time-nuts
> > >> and follow the instructions there.
> > >>
> > >>  _______________________________________________
> > > time-nuts mailing list -- time-nuts at febo.com
> > > To unsubscribe, go to https://www.febo.com/cgi-bin/
> > > mailman/listinfo/time-nuts
> > > and follow the instructions there.
> > >
> >
> >
> > ------------------------------
> >
> > Message: 3
> > Date: Wed, 4 Mar 2015 10:20:45 -0800
> > From: "Tom Van Baak" <tvb at LeapSecond.com>
> > To: "Discussion of precise time and frequency measurement"
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID: <231A4CB7D0CB45CAAF6A3015A4900374 at pc52>
> > Content-Type: text/plain; charset="utf-8"
> >
> > Martyn -- the 74AC spec allows Vcc to go up to 6.0 VDC (absolute max is
> > 7.0 VDC) so that might help you meet your 4.5 VDC goal, especially if
> this
> > is for play and not a product. Pick the resistors and use more than 3
> gates
> > if necessary. Note the peak current spec is 50 mA per gate. Not sure what
> > the combined gate current limit is; there is a package thermal limit. You
> > also have to decide if you want some level of short-circuit protection or
> > if you can always assume 50R termination.
> >
> > John -- have you tried long duration output shorts on the TADD-2? I
> > figured that was also a reason for each gate having its own resistor.
> >
> > /tvb
> >
> >
> >
> > ------------------------------
> >
> > Message: 4
> > Date: Wed, 04 Mar 2015 12:03:16 -0800
> > From: Hal Murray <hmurray at megapathdsl.net>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Cc: hmurray at megapathdsl.net
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID:
> > <20150304200316.6AFBC406057 at ip-64-139-1-69.sjc.megapath.net>
> > Content-Type: text/plain; charset=us-ascii
> >
> >
> > jra at febo.com said:
> > > Per Tom Clark, who came up with the idea, they are *not* intended to
> > > provide a near-end line termination to 50 ohms, but are simply there to
> > > protect the paralleled devices if the gates have slightly different
> > delays
> > > (in which case one gate could end up sinking the other two).
> >
> > Is that a real problem?  How far off can the prop delay be for 2 gates on
> > the
> > same chip?
> >
> > I seem to remember reading something saying it was OK to just wire them
> up
> > in
> > parallel.  It could have been an app note, or it could have been a rumor
> on
> > usenet.
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
> >
> >
> > ------------------------------
> >
> > Message: 5
> > Date: Wed, 04 Mar 2015 15:57:56 -0500
> > From: Dan Kemppainen <dan at irtelemetrics.com>
> > To: time-nuts at febo.com
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID: <54F771D4.4010500 at irtelemetrics.com>
> > Content-Type: text/plain; charset=utf-8; format=flowed
> >
> > Hi,
> >
> > Correct me if I'm wrong but being that AC series gates are MOS devices,
> > isn't there inherent current limiting in the MOS junction itself? I
> > would think that for the few nanoseconds of skew across gates the tens
> > of ohms of junction resistance would make 'shoot through' negligible in
> > terms of heating and gate damage.
> >
> > Of course, a TTL device would be a completely different story and I
> > would fully expect summing or balancing resistor would be needed there.
> >
> > Does anyone have further input regarding paralleling MOS logic devices?
> >
> > Dan
> >
> >
> >
> > > One comment on the parallel AC gate approach.  It may not be directly
> > > applicable to Martyn's issue, but there is a common confusion about the
> > > value of the summing resistors.
> > >
> > > Per Tom Clark, who came up with the idea, they are*not*  intended to
> > > provide a near-end line termination to 50 ohms, but are simply there to
> > > protect the paralleled devices if the gates have slightly different
> > > delays (in which case one gate could end up sinking the other two).
> > >
> > > So, the commonly used 47 ohm value isn't magic.  You can use a lower
> > > value, and thus get more voltage at the far end.  I haven't
> experimented
> > > to see how far you can take that idea before destroying gates.
> > >
> > > John
> >
> >
> > ------------------------------
> >
> > Message: 6
> > Date: Wed, 04 Mar 2015 17:44:09 -0600
> > From: Didier Juges <shalimr9 at gmail.com>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] Trimble Thunderbolt NMEA ?
> > Message-ID: <EF4EDC38-C96B-402F-AB2F-9AC273AB399C at gmail.com>
> > Content-Type: text/plain; charset=UTF-8
> >
> > The code is in C and Silabs has small dev kits (Toolsticks) that cost $10
> > to which you need to add $18 for the programming dongle. A little more
> > expensive than an Arduino, or less, depending on where you buy it...
> >
> > To that you need to add a MAX232 (or two serial-TTL adapters at $4 each
> or
> > so on ebay) and you are in business.
> >
> > Total cost about the same as a dedicated GPS receiver with antenna and
> > NMEA output. Choose your poison :)
> >
> > Didier KO4BB
> >
> >
> > On March 3, 2015 10:23:56 PM CST, Chris Albertson <
> > albertson.chris at gmail.com> wrote:
> > >Is the code in C?  If so I bet it would run on some development board.
> > >No
> > >need to make custom PCBs.
> > >
> > >On Tue, Mar 3, 2015 at 5:00 AM, Didier Juges <shalimr9 at gmail.com>
> > >wrote:
> > >
> > >> Tim,
> > >>
> > >> It shouldn't be too hard to modify the code for my Thunderbolt
> > >monitor to
> > >> make it into a TSIP->NMEA converter. The last version of the kit has
> > >a uC
> > >> with two serial ports. I m out of the kits at the moment but I have a
> > >few
> > >> spare boards left over.
> > >>
> > >
> > >--
> > >
> > >Chris Albertson
> > >Redondo Beach, California
> > >_______________________________________________
> > >time-nuts mailing list -- time-nuts at febo.com
> > >To unsubscribe, go to
> > >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > >and follow the instructions there.
> >
> > --
> > Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do
> > other things.
> >
> > ------------------------------
> >
> > Message: 7
> > Date: Wed, 4 Mar 2015 18:47:13 -0500
> > From: Bob Camp <kb8tq at n1k.org>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID: <EFC260CC-CAF3-4021-8EF9-27540AE57494 at n1k.org>
> > Content-Type: text/plain; charset=utf-8
> >
> > Hi
> >
> > If you want to drive out of a 50 ohm source into your 50 ohm load *and*
> > get 5V into the load … that’s a fancy amp. 10V power and some careful
> > work to get it going.
> >
> > If you just want to get roughly 5V into a 50 ohm load, then it’s a matter
> > of how
> > many gates you decide to parallel. If you go with “32 ma” drivers, you
> > should
> > be able to get it done with 8 of them in parallel. Drive them all off of
> a
> > single
> > dedicated fast gate that’s on the same supply. Probably best to stuff
> > a 20 or 30 ohm resistor in series with each of the outputs. If it’s *got*
> > to
> > be a full 5V, don’t use the resistors.
> >
> > Bob
> >
> > > On Mar 4, 2015, at 5:26 AM, Martyn Smith <martyn at ptsyst.com> wrote:
> > >
> > > Hello,
> > >
> > > A quick question.
> > >
> > > My output driver for a simple amplifier.
> > >
> > > I use three gates (in parallel with resistors) from a 74AC14 to give me
> > about 0-3.2V into 50 ohm.
> > >
> > > I want to have a driver that gives me a full 0-5V (at least 0-4.5V)
> > swing into 50 ohms.
> > >
> > > Can anyone recommend an IC that can delivery this.
> > >
> > > But it needs to have similar jitter performance to the 74AC14.
> > >
> > > I use it up to 10 MHz.
> > >
> > > Best Regards
> > >
> > > Martyn
> > >
> > > _______________________________________________
> > > time-nuts mailing list -- time-nuts at febo.com
> > > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > > and follow the instructions there.
> >
> >
> >
> > ------------------------------
> >
> > Message: 8
> > Date: Wed, 04 Mar 2015 19:44:29 -0500
> > From: Charles Steinmetz <csteinmetz at yandex.com>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] 50 ohm Driver
> > Message-ID: <20150305034434.iYveMp4n at smtp12.mail.yandex.net>
> > Content-Type: text/plain; charset="us-ascii"; format=flowed
> >
> >
> > >Is [one gate sourcing or sinking current into paralleled gates that
> > >don't switch at
> > >exactly the same time] a real problem?  How far off can the prop
> > >delay be for 2
> > >gates on the same chip?
> > >
> > >I seem to remember reading something saying it was OK to just wire them
> > up in
> > >parallel.  It could have been an app note, or it could have been a rumor
> > on
> > >usenet.
> >
> > Most manufacturers sanction direct paralleling of gates on the same
> > chip (and forbid any paralleling, ballasted or otherwise, of outputs
> > from different chips).  However, there are other considerations
> > (short-circuit protection, maximum output current rating per gate,
> > maximum supply and/or ground current rating per package, maximum
> > power dissipation, etc.).  Good design practice is to put series
> > resistors on each gate output that will prevent any of these ratings
> > from being exceeded into a short circuit to ground or to Vcc.  For
> > HC, AC, NC7NZ, and NC7SZ, the per-gate output current rating is +/-
> > 24 (or 25) mA, which suggests that each gate should have a 200 ohm
> > series resistor -- but you need to check all of the other ratings
> > mentioned above for the chip you use, to make sure they won't be
> violated.
> >
> > Unfortunately, if the load is 50 ohms to ground, pulling it to even
> > 4.5v from a 5v logic supply requires a source resistance of only 5.6
> > ohms, or 36 parallel gates each with 200 ohms in series (this assumes
> > that the gates can pull all the way to 5v while delivering rated
> > current, which they can't -- so the reality is even worse).  You can
> > make things a little better by terminating the output into 50 ohms to
> > 1/2 Vcc (i.e, the center of a voltage divider with 100 ohms to Vcc
> > and 100 ohms to ground), but (i) it only gets a little better, and
> > (ii) now it won't pull all the way to ground.
> >
> > All that said, why do you want to generate a high-current square
> > wave, anyway?  If you're distributing a frequency standard, it is
> > much better to distribute a sine wave (you don't have to worry about
> > the harmonics being skewed, and there is exponentially less of a
> > problem with it radiating and getting into every radio and other
> > sensitive electronic device in your house and the other houses on the
> > block).
> >
> > Best regards,
> >
> > Charles
> >
> >
> >
> >
> >
> > ------------------------------
> >
> > Message: 9
> > Date: Thu, 05 Mar 2015 01:27:23 +0000
> > From: Angus <not.again at btinternet.com>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] new tdc from Texas
> > Message-ID: <uu9ffapgkl5t7qnv73m9v7j2ba5mttl0u6 at 4ax.com>
> > Content-Type: text/plain; charset=us-ascii
> >
> > Hi,
> >
> > I've not seen any mention of anything other than the TDC1000.
> >
> > I was a bit surprised that they went down the less-integrated route
> > and separated the TDC, but it turns out that for a lot of the sort of
> > things they designed it for, a uC provides good enough timing itself,
> > and no extra TDC is needed at all.
> >
> > I see that Acam have released a bit more info on their new GP30,
> > although no data sheet yet. It quotes typical LSB of 11ps, and rms
> > noise of 1.2 LSB, which is quite an improvement on the GP22.
> > It would just be good if they offered a simple online way of getting
> > low volumes of them - I suspect that the specialist distributors would
> > be just as happy as the customers would be!
> >
> > Angus.
> >
> >
> > On Tue, 03 Mar 2015 15:43:25 -0800, you wrote:
> >
> > >Hi Angus:
> > >
> > >Do you know if they have an IR pulse front end which would be more
> > interesting than the ultrasonic front end?
> > >
> > >Mail_Attachment --
> > >Have Fun,
> > >
> > >Brooke Clarke
> > >http://www.PRC68.com
> > >http://www.end2partygovernment.com/2012Issues.html
> > >http://www.prc68.com/I/DietNutrition.html
> > >Angus wrote:
> > >> In case anyone is interested, the full data sheet is on the TI site
> > >> now, although I didn't see any actual IC's yet other than the ones in
> > >> the eval boards.
> > >>
> > >> Angus.
> > >>
> > >>
> > >> On Tue, 17 Feb 2015 21:24:08 -0200, you wrote:
> > >>
> > >>> Initial datasheet:
> > >>>
> > >>> http://www.ti.com/lit/ds/symlink/tdc7200.pdf
> > >>>
> > >>> EVM:
> > >>>
> > >>> http://www.ti.com/tool/tdc1000-tdc7200evm
> > >>>
> > >>> Seems good... what do you think?
> > >>>
> > >>> Daniel
> > >>> _______________________________________________
> > >>> time-nuts mailing list -- time-nuts at febo.com
> > >>> To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > >>> and follow the instructions there.
> > >> _______________________________________________
> > >> time-nuts mailing list -- time-nuts at febo.com
> > >> To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > >> and follow the instructions there.
> > >>
> > >
> > >_______________________________________________
> > >time-nuts mailing list -- time-nuts at febo.com
> > >To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > >and follow the instructions there.
> >
> >
> > ------------------------------
> >
> > Message: 10
> > Date: Thu, 5 Mar 2015 08:56:23 +0100
> > From: Attila Kinali <attila at kinali.ch>
> > To: Discussion of precise time and frequency measurement
> > <time-nuts at febo.com>
> > Subject: Re: [time-nuts] new tdc from Texas
> > Message-ID: <20150305085623.cb5218ab541d5ffaf13dcfcb at kinali.ch>
> > Content-Type: text/plain; charset=US-ASCII
> >
> > On Thu, 05 Mar 2015 01:27:23 +0000
> > Angus <not.again at btinternet.com> wrote:
> >
> > > I've not seen any mention of anything other than the TDC1000.
> > >
> > > I was a bit surprised that they went down the less-integrated route
> > > and separated the TDC, but it turns out that for a lot of the sort of
> > > things they designed it for, a uC provides good enough timing itself,
> > > and no extra TDC is needed at all.
> >
> > I think the main application TI intended it for is for ultrasonic
> > flow meeters (like [1]). There you have quite small and bounded
> > start-stop delays. With this they can get into the growing electronics
> > for low energy building market.
> >
> > In contrast to that, the Acam devices seem to be general purpose TDCs
> >
> >
> > Attila Kinali
> >
> >
> > [1] http://www.shk-profi.de/imgs/52579203_0d4dd378d4.jpg
> > --
> > < _av500_> phd is easy
> > < _av500_> getting dsl is hard
> >
> >
> > ------------------------------
> >
> > Subject: Digest Footer
> >
> > _______________________________________________
> > time-nuts mailing list
> > time-nuts at febo.com
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >
> > ------------------------------
> >
> > End of time-nuts Digest, Vol 128, Issue 5
> > *****************************************
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