TTL to MECL via selected IC

Discussion in 'General Electronics Chat' started by Management, May 20, 2008.

  1. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I have been away for a while but I'm back with a problem. I do not know if this belongs in another section or what vbut I know it is not HW.

    I have an OnSemi MC10H124 Quad TTL-to-MECL Translator w/ TTL Trobe Input.

    I want to translate TTL 0V/+5V to MECL -5.2V/0V. The IC is powered with:
    Vcc = +5v
    Vee = -5.2V
    GND = GND

    I know how the device works from the data sheet. But I can't help but wonder if I can just connect this up to the TTL inputs and connect to straight to the MECL inputs and it would work or would I have to use some RLCs to maintain stability, etc.

    Can somone let me know the ins and outs of using this device? RCLs that would surround it, if any? Schematic would help or an application note. Haven't really seen one that applies.

    The output would be connected to another chip that takes differential MECL in and some none differential. Would I have to put some sort of passive (RLCs) inbetween, if so why?

    Thank you. I Hope I explained my situation enough for someone to point me in the right direction.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    I suggest you go to ON Semiconductor's site:
    http://www.onsemi.com
    and download AN1672, "The ECL Translator Guide".

    It's been a long time since I've fiddled with ECL. Need to be careful about where you put terminating/pull-up resistors. The last ECL board I put together made a nice room heater. :eek:
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    From the spec sheet, it should go with no further components. All ECL chips output the signal and it's inverse, or so I recall from using the stuff a long time ago. The worst problem is the very short distance you can send the ECL signal without having to use a differential transmitter/receiver.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    You have to use two capacitors 0.1uF each between ground and Vcc and between ground and Vee to supply the transient (rapid changes in current) currents of the IC. On the datasheet it is said that the IC can source (output) 50mA of continuous current. You can connect it directly to the TTL outputs and ECL inputs but be aware not to connect many inputs on one output and draw more than 50mA.
     
  5. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Thank you for the reminder on the power supply caps. Also, the chip that takes the MECL input ( Low = -5.2 V & High = 0 V) states in its specs under termination type "3mA Output". Going by what you stated, this would be ok to connect straight to the translator or would there be other things to worry about?

    I would like all there information everyone can think of so I can do some reading and understand.

    Thank you Sgt, I printed that out and will be reading it later today. Also, thank you beenthere.

    If you would like to add anything more please do.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    My experience with ECL is -.7 is a 0, -1.4 is a 1. The reason for their extreme speed is they don't move very far voltage wise.
     
  7. mik3

    Senior Member

    Feb 4, 2008
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    Well, i never worked with ECL but if you connect one one input of the ECL to the output of the translator i guess it will be fine. I dont think the ECL input will draw more than 50mA !!!
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    ECL was faster than TTL by a long shot, but ate a lot of power. I do not recall figures, but all the transistors are saturated all the time (the logic voltage levels represent turn on and max conduction), so 50 ma/chip is quite possible. High-low transitions will let you know if your o'scope has the stated bandwidth.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    MECL is the nearest thing to analog digital will get. Many cases the transistors aren't saturated, which is why it is high speed. You ever look at the fundamental schematics of an ECL gate it looks a lot like a high speed differential amplifier.

    When I worked on lightwave we dealt with digital speeds in excess of 10GB/sec, and last I've heard it was over 40GB/sec. The front end is the highest speed of course, they demultiplex it down as quickly as they can to get it into the realm of conventional logic. A simple flipflop, the first stage of the demuxed signal, was very hot indeed. In general, the faster an ECL gate is the hotter it runs, even in steady state. The families of the logic changed after each transistion too, the front end, the 10GB/sec, was different than but compatible with the second set of flipflops, and so on, until it was in the realm of high speed CMOS logic. Never priced them, but I bet those really high speed gates were expensive!

    ECL only exists because of it's high speeds. I personally prefer working with CMOS.
     
    Last edited: May 20, 2008
  10. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Ok Ifrom what I understand the output of the IC mention above (the translator) will be going to another IC whose inputs are only concerned with voltage not current, ie transistors. A low is -5.2 and a high is 0 (MECL).

    Should I be putting the output of the translator IC directly to the input of my second IC or should I be putting current limiting resistors in series or some resistors to ground so the current has a path to ground? Also why? I am kind of confusing myself.

    I'm still a young engineer and I have all this stuff I learned in my head but get confused when I start to use it.

    Thanks in advance.
     
  11. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Also, the input of the translator will be coming from a Digital I/O for USB card (NI USB-6509) that is capable of 5V TTL output (Input as well). Therefore I don't need anything else and can just connect it directing to the translator. Am I correct in this assumption or do I need a pull up network or something else?
     
  12. mik3

    Senior Member

    Feb 4, 2008
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    You can connect them directly.
     
  13. Management

    Thread Starter Active Member

    Sep 18, 2007
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    OK I am having a few problems.

    Data Sheet: http://www.onsemi.com/pub_link/Collateral/MC10H124-D.PDF

    The OnSemi MC10H124 that I am using does not seem to work the way I am reading. Basically I can't get an output.

    I have +5 V @ Vcc and -5.2 V @ Vee with GND connected to GND of course. Caps are at the supplies.

    According to the data sheet, "When the common strobe input [pin 6] is at a low-logic level, it forces all true outputs to a MECL low-logic state and all inverting outputs to a MECL high-logic state."

    The way I understand this is if I GND the strobe input and also GND lets says input A (pin 5), then this should result in a true and I should get a MECL low-logic state of -5.2 V on pin 2 which is the output and a 0 V on pin 4 which is the inverting output of output A. Correct?

    I don't see why this wouldn't work. So I put a high on pin 5 and get nothing at the outputs (pin 2 & 4). I also put high on both the strobe (pin 6) and the input A (pin 5) and still get nothing at the outputs for A (pin 2 & 4).

    Note: I am using a breadboard (proto board) and there are only caps at the supplies.

    Can someone help me test this IC? Thank you.
     
    Last edited: May 27, 2008
  14. Wendy

    Moderator

    Mar 24, 2008
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    Like I said, MECL uses voltage states of -.7V and -1.4V, not -5V.
     
  15. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I thought MECL and ECL were different since you said on the first page "ECL". I was told that it would output -5.2 V and 0 V.

    I still want to get this IC to work so can you or anyone else help me. I took a closer look at the datasheet and indeed Bill Marsden is correct. I am still not getting those output voltages. The output just sits at 0 V for both A output and the inverting A output. Why is that?

    I guess my goal is to now go from this MECL output to -5.2 V (low) and 0 V (high).
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    Show us what you have wired so far, if you will.

    MECL and ECL are basically the same thing. Emitter Coupled Logic is the common denominator.
     
  17. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Thank you for responding. I figured out what was wrong. A lot of the time it helps just to talk to someone. The problem was that I didn't have the outputs connected with 50 Ohms to -2V like the datasheet says in small print. :mad:

    Any easy ways to go from this MECL to -5 V (low) and 0 V (high)? Using this IC to also driving some differential inputs. All inputs are the above stated control.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    I may be wrong, but I think ECL has to have pull down resistors. I'll have to dig up my old text book on the subject.
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    How fast do you need it to be? Do you absolutely need the -5V? My last post was made before I saw yours. Been a while since I've worked with ECL.

    ECL is fundimentally differential amps wired as logic, which is where the speed and heat come from. If you HAVE to have the -5 then I would go with a fast transitor differential amp.
     
    Last edited: May 27, 2008
  20. mik3

    Senior Member

    Feb 4, 2008
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    As i can see from the datasheet when you have a low logic to the strobe input you drive the non-inverted outputs to a low logic and the inverted outputs to a high logic but you cant change their values if you change the data on your TTL inputs.
     
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