[time-nuts] 50 ohm driver

Fri Mar 6 03:20:30 UTC 2015

Martyn,
How long is the cable you are driving? If you have large ground
differentials you may destroy the chips very easily. Especially if between
industrial buildings.
Some of the things discussed here are fine for a hobby environment but
somewhat questionable in a commercial business.
Regards
Paul
WB8TSL

On Thu, Mar 5, 2015 at 4:59 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
>
> _______________________________________________
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> ------------------------------
>
> End of time-nuts Digest, Vol 128, Issue 5
> *****************************************
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