We stock the MC10EP89, which is a great part, but it's kinda slow. I was thinking that adding a couple of diodes, and maybe inductors, could speed it up, given a single 3.3 volt supply. The next chip will be CML compatible and doesn't need much swing.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Can U bootstrap its supply from the outputs?
How would that work?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Are the outputs open-emitter e.g.:
?
the idea is that the supply rails float up and down a bit so you get the available-drive-power advantages of operating from a "virtual" 5 v supply without actually making the output Q bases swing more than they would @ 3.3
Would bootstrapping for Q not un-bootstrap for not_Q? The EP89 already has double output voltage swing.
If the outputs are open-emitter as in the simplified ECL-buffer schematic (it's clearly a somewhat more complex IC from the datasheet, and they don't show you all the insides) then positive-going is an emitter-loaded transistor switch to the positive supply and negative-going is an external resistor pull-down to ground.
in that situation the only thing that's being boostrapped is the positive-going drive supply, and the diff pairs; their collectors are always operating somewhere in the linear region they don't "care" where the supplies are exactly
so at quiescent you could do 3.3 and 0, Q goes up, pulls positive supply up to 5 and also a bootstrap to make "ground" pull up to 1.7, you get 5V drive for Q, and looks to me like not-Q still pulls down to ground same as before
The double swing probably slows it down, especially on the negative swing with the passive pulldown. Vlow is only about 1.5 volts above ground, so the pulldown resistor current is low. The inductors might improve the pulldown edge by sustaining the current for a while.
I've tried Spicing this, but I didn't have a believable ECL model... just something I've hacked out of transistors.
Hints are that a resistor between the complementary ECL outputs is a better speedup than the diodes.
Time to Dremel, I guess.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Found this:
which includes the proper transistor models.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Have you looked at the NBSG16M? 10GHz CML:
"The NBSG16M is a differential current mode logic (CML) receiver/driver. The device is functionally equivalent to the EP16, LVEP16, or SG16 devices with CML output structure and lower EMI capabilities.
Inputs incorporate internal 50 Ohm termination resistors and accept NECL (Negative ECL), PECL (Positive ECL), LVTTL, LVCMOS, CML, or LVDS. The CML output structure contains internal 50 Ohm source termination resistor to VCC. The device generates 400 mV output amplitude with 50 Ohm receiver resistor to VCC."
Features: Maximum Input Clock Frequency > 10 GHz Typical
Maximum Input Data Rate > 10 Gb/s Typical
120 ps Typical Propagation Delay35 ps Typical Rise and Fall Times
Positive CML Output with Operating Range: VCC = 2.375 V to 3.465 V with VEE = 0 V
Negative CML Output with RSNECL or NECL Inputs with Operating Range: VCC =
0 V with VEE = -2.375 V to -3.465 VCML Output Level; 400 mV Peak-to-Peak Output with 50 _ Receiver Resistor to VCC
50 Ohm Internal Input and Output Termination ResistorsCompatible with Existing 2.5 V/3.3 V LVEP, EP, LVEL and SG Devices
VBB Reference Voltage Output
The key is that current into the collectors is steered, so the common path inductance doesn't matter, and the separate collector inductances are really tiny because they're adjacent on-chip. So when one transistor turns on, it doesn't have to wait long for current to start flowing into its collector.
especially on the negative
I've heard (but never tried) that a lower power supply voltage speeds ECL up (at some cost in logic margin, of course). That should be easy to test, or simulate.
It makes sense that reducing the collector diode depletion layer would do that.
The output transistor collector goes to Vcc, and the base pulls up to same, and the output is an emitter follower. The transistor hardly knows how far away Vee is.
The external pulldown resistor current does change, depending on Vcc-Vee. The change in pulldown current is worse for the big-swing EP89 than it is for regular-swing parts.
I figure that the EP89 will get faster if I force the voltage swing down.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
if it's used as a line-driver surely charging and discharging the single-ended component of the line capacitance is the dominating factor?
Have you looked at the MC100EP16? 4 GHz
$8.42 Mouser
I once fell on the nose with a 2.5/3.3 (maybe 3.3/5V) ECL chip. The idea was to level shift a signal in a cheap way by abusing the common mode range on the input/output side and shifting the supply voltage by a diode drop or two.
That did not work. Re-checking the data sheet, there was 2v5 _OR_ 3V3. They must have had a bandgap or whatever and switched operating points. It did not work at all in between. IIRC the chip was from Synergy.
cheers, Gerhard
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