I have to use an adapter board and traces are probably longer than they should be. For traces above I will cut the wires to the same length to equalize propagation delays regardless of if they need that length or not. Unfortunately, the adapter board itself has varying lengths on the traces.
Is it that simple or am I being naive about ECL circuits? Thanks.
With signal rise times (10 percent-90 percent) of 750 ps,
open line stub lengths must be less than 0.5 in to hold reflections
under 35 percent overshoot and under 12 percent
undershoot. Larger reflections can saturate gate inputs and
reduce noice immunity. Longer signal runs must use transmission
lines terminated in the line characteristic impedance.
The CRAY-1 boards have 7-mil wide lines and 7-mil spaces.
The 7-mil height above a ground (or power) plane results in
a 60-52 microstrip line with a delay of 0.15 ns/in.
If you have any kind of trace length (i.e., comparable to the rise time -- 100ps is only 2cm of trace or coax), you will need termination resistors. And I forget, but suspect, that ECL needs/wants a termination resistor for correct bias anyway. Follow the datasheet instruction with termination resistors and terminating voltage: bypass the termination resistor to ground as short as possible, using chip resistors/capacitors and ground plane. The termination supply can be generated with an op-amp or something like that; it should be capable of bidirectional current flow (so, don't just use an LM317 or something). Be sure it can handle plenty of current.
Likewise, your maximum frequency will be limited by propagation delay of the gates as well as the interconnects. Should still be around a GHz though!
Tim
Following this thread I built myself an oscillator, actually four so far, that work well out of 7404, 74LS04, 74LS14, and 74HC04 ICs (they all run 19-22Mhz except the Schmitt trigger one which runs more like 12Mhz). I took the advice of the person who told me I should be the person to test out an ECL circuit and I am going to attempt to build that too, but I don't know anything about ECL so I think I will ask for some advice here.
it doesn't have to be a ring (3x gates). One gate works just fine - connect its input to its output.
If you have any kind of trace length (i.e., comparable to the rise time -- 100ps is only 2cm of trace or coax), you will need termination resistors. And I forget, but suspect, that ECL needs/wants a termination resistor for correct bias anyway. Follow the datasheet instruction with termination resistors and terminating voltage: bypass the termination resistor to ground as short as possible, using chip resistors/capacitors and ground plane. The termination supply can be generated with an op-amp or something like that; it should be capable of bidirectional current flow (so, don't just use an LM317 or something). Be sure it can handle plenty of current.
Likewise, your maximum frequency will be limited by propagation delay of the gates as well as the interconnects. Should still be around a GHz though!
Tim
Looks like you are off to a good start. Check the pg 8 of the data sheet you provided the link to for the termination. VTT=VCC-2.0. I would use that last gates to drive the DSO. I checked and only have the real old 80s Motorola book that covers the 10K and earlier. Does not seem like you would want the series terminator but could be wrong.
By using the last gate to "drive the DSO" are you meaning the RF output and assuming an oscilloscope on the output? What advantage does this give, will having a buffer square up the output a bit since it is no longer also driving a gate?
I am only suggesting to check the data sheet. Micrel app note you link to, see figures 3&4. Take the time to read it.
Zo is not a resistor.
Adding any discontinuity, like a zero ohm jump will cause some reflection. Higher speeds, need to pay more attention.
You could make a few different boards on the one panel to try different ideas out.QuoteBy using the last gate to "drive the DSO" are you meaning the RF output and assuming an oscilloscope on the output? What advantage does this give, will having a buffer square up the output a bit since it is no longer also driving a gate?
Yes. Isolation.
I have not used ECL in many years. You should have no problem getting something to work on a circuit board. This is a very short video I put together showing a single PECL FF on an a VERY crude X-acto knife board. The videos not real exciting but does show you can clock some of them well into the GHz range as mentioned.
https://www.youtube.com/watch?v=k1pUlJwJzAI&feature=youtu.be
Looking forward to seeing what you get working.
"As a result of ECL/PECL’s differential, high input impedance, very low output impedance (Open Emitter), and small signal swing (andresulting low EMI), ECL/PECL is ideal for driving 50? and 100? controlled impedance transmission lines. A signal trace is considered a transmission line, thus requiring termination, when the signal’s rise/fall time is faster than a trace’s round-trip propagation delay. In some applications, if the distance between two devices is short enough, then termination may not be necessary. Another way to express this is: If, T RISE(signal) < 2 × TPD(trace), then the trace is a transmission line and proper termination is required"
My idea of a regulator to supply 3.0V for the 50 ohm parallel terminator resistors, is that a good idea?
Potato semi's so called GHz logic might be interesting to play with/try. Parts can be had from their on-line store in small qty.
http://www.potatosemi.com/
Potato semi's so called GHz logic might be interesting to play with/try. Parts can be had from their on-line store in small qty.
http://www.potatosemi.com/
I am sort of surprised I haven't heard of them and never got a hit on them on eBay during other searches. Sort of interesting. I do think they need a new logo and name though, the current choices are pretty lame. I know it doesn't matter as far as their product goes, but really it does actually matter at some point to generate enough confidence that the company is a serious entity that will be there in a few years. I wonder if they have any serious customers.