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LVPECL to 3.3V CMOS Levels

P

pfitz

Jan 1, 1970
0
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they expensive?

Or is there a cheaper way of doing this perhaps with a High frequency
OP-Amp?

bearing in mind that I don't care what the output looks like as long as it
crosses the CMOS thresholds.


pfitz


regards

PFitz
 
F

Fred Bloggs

Jan 1, 1970
0
pfitz said:
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they expensive?

Or is there a cheaper way of doing this perhaps with a High frequency
OP-Amp?

bearing in mind that I don't care what the output looks like as long as it
crosses the CMOS thresholds.


pfitz


regards

PFitz

Which phase detector are you using?
 
R

Rene Tschaggelar

Jan 1, 1970
0
pfitz said:
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they expensive?

Or is there a cheaper way of doing this perhaps with a High frequency
OP-Amp?

bearing in mind that I don't care what the output looks like as long as it
crosses the CMOS thresholds.

You shouldn't consider 155MHz for CMOS. Way too high.
Use a differential input phase detector.
BTW, there are PLL chips, that do everything for you.

Rene
 
J

Jim Thompson

Jan 1, 1970
0
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they expensive?
[snip]
regards

PFitz

Yes available, cost I don't know, try: http://www.azmicrotek.com/

...Jim Thompson
 
P

pfitz

Jan 1, 1970
0
Just using a digital phase detector in a (xilinx) CPLD, the outputs of which
will drive an Analog Filter.

I realise the frequency is rather high for CMOS but if the tracks are kept
short would that still be such a problem.

I mean when you have CPUs with front side busses of 133Mhz and above, surely
they must be converted to CMOS, no?

pfitz
 
J

John Larkin

Jan 1, 1970
0
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they expensive?

OnSemi, maybe Synergy too, has these. Look at the 10ELT parts. They
are a bit slow, in my experience.
Or is there a cheaper way of doing this perhaps with a High frequency
OP-Amp?

An fast opamp would work, but that's probably overkill. Cooler would
be a 3.3v CMOS LVDS line receiver, like one of the National or TI
parts. They are cheap and blindingly fast, and should work directly
with the LVPECL, or maybe with a small level shift, easily done with a
couple of R-Cs in the pecl pulldowns.
bearing in mind that I don't care what the output looks like as long as it
crosses the CMOS thresholds.

Would you object to a near-perfect square wave?

John
 
J

John Larkin

Jan 1, 1970
0
You shouldn't consider 155MHz for CMOS. Way too high.

Not any more. You can buy 400 MHz cmos LVDS parts, and I'm now using a
Tiny Logic flipflop with 1 ns typ Tpd; that's as fast as 10KH ECL.

Aren't Pentiums scheduled to clock at 10 GHz in a couple of years?

John
 
J

John Larkin

Jan 1, 1970
0
Yes available, cost I don't know, try: http://www.azmicrotek.com/

...Jim Thompson

Their ecl/ttl converter (10ELT21? I forget) is a cmos part, and it's
actually a lot better than the Moto/OnSemi equivalent, which uses some
old MosaicII or somesuch bipolar process and has weird jitter issues.

John
 
J

Jim Thompson

Jan 1, 1970
0
Their ecl/ttl converter (10ELT21? I forget) is a cmos part, and it's
actually a lot better than the Moto/OnSemi equivalent, which uses some
old MosaicII or somesuch bipolar process and has weird jitter issues.

John

Yep, I like their parts... I've done a *lot* of design work for
Arizona Microtek ;-)

They're in Mesa, AZ.

...Jim Thompson
 
R

Rene Tschaggelar

Jan 1, 1970
0
John said:
Not any more. You can buy 400 MHz cmos LVDS parts, and I'm now using a
Tiny Logic flipflop with 1 ns typ Tpd; that's as fast as 10KH ECL.

Aren't Pentiums scheduled to clock at 10 GHz in a couple of years?


I too measured a risetime of 450ps on an CMOS output of an FPGA,
however this signal is not meant to be routed as no impedance
is given. Those signals meant to be routed are usually
differential at that speed and an impedance is specified.


Rene
 
J

John Larkin

Jan 1, 1970
0
Yep, I like their parts... I've done a *lot* of design work for
Arizona Microtek ;-)

They're in Mesa, AZ.

...Jim Thompson


They are very nice people. I talked to the Prez (Harold?) about my
ELT21 problem, sent him scope shots of the Moto jitter, and got
samples with his hand-scrawled note; what's the chances of my being
able to talk to the president of Motorola?

http://www.azmicrotek.com/

Buy their stuff! It's good!

John
 
J

Jim Thompson

Jan 1, 1970
0
They are very nice people. I talked to the Prez (Harold?) about my
ELT21 problem, sent him scope shots of the Moto jitter, and got
samples with his hand-scrawled note; what's the chances of my being
able to talk to the president of Motorola?

http://www.azmicrotek.com/

Buy their stuff! It's good!

John

Yep, I've been working with Harold Muller for close to 20 years.

...Jim Thompson
 
M

Mac

Jan 1, 1970
0
Just using a digital phase detector in a (xilinx) CPLD, the outputs of which
will drive an Analog Filter.

I realise the frequency is rather high for CMOS but if the tracks are kept
short would that still be such a problem.

I mean when you have CPUs with front side busses of 133Mhz and above, surely
they must be converted to CMOS, no?

Those busses use some pretty fancy schemes to maintain signal integrity.
They have termination resistors which pull to a termination voltage
(typically half the signalling voltage) and they have a switch threshold
input that is supposed to be held at that same termination voltage.

But If the CPLD seems to be spec'd to work at the speeds you are
proposing, you should be alright.

I would recommend that you put a series resistor near the source, and a
shunt capacitor near the load. You can always use a zero-ohm resistor and
leave the capacitor unpopulated, but if you need them later and the pads
aren't there, then you'll be out of luck.
pfitz

expensive?

You've already got a couple of suggestions. I'll just point out that you
could probably use almost any differential receiver spec'd for 3.3 volt
operation and ( the right switching speed). For example, an LVDS
transceiver might work. You just have to make sure you respect the common
mode voltages.

I wouldn't use an op-amp. Generally, all the things that make op-amps good
op-amps make them lousy high speed logic chips. But there are a lot of
high-speed comparators that might do the job.

[snip]

Mac
--
 
F

Fred Bloggs

Jan 1, 1970
0
This is a straightforward LVECL->LVCMOS and can be done typically up to
350MHz. The most readily available part will be the ONSemi MC100EPT23 at
$8/ea small quantity. Others are the Micrel SY100EPT23L and SY89323L,
and ICST ICS83023I.
 
R

raymund hofmann

Jan 1, 1970
0
pfitz said:
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they
expensive?

Lots of expensive parts. But they work and you don't have to do much
"analog" design.
Or is there a cheaper way of doing this perhaps with a High frequency
OP-Amp?

How about "MECL SYSTEM DESIGN HANDBOOK" pg 212 Fig 9b ?
If you use a PNP like BFT92 for the 2N3906 and maybe do some level
shifting for the differential ECL signals / output signal you should be
able to cheaply do it. And maybe some termination at the CMOS receiving
side.
I managed to convert 3ns wide pulses and process them in a CMOS ASIC
this way.

Raymund Hofmann
 
F

Fred Bloggs

Jan 1, 1970
0
raymund said:
Lots of expensive parts. But they work and you don't have to do much
"analog" design.




How about "MECL SYSTEM DESIGN HANDBOOK" pg 212 Fig 9b ?
If you use a PNP like BFT92 for the 2N3906 and maybe do some level
shifting for the differential ECL signals / output signal you should be
able to cheaply do it. And maybe some termination at the CMOS receiving
side.
I managed to convert 3ns wide pulses and process them in a CMOS ASIC
this way.

Raymund Hofmann

You're welcome to firm up that design using a single 3.3V/GND power
supply....
 
J

John Larkin

Jan 1, 1970
0
Hi all,

I'm designing a PLL which will give an output frequency of 155.52MHz in
LVPECL. I was wondering if anyone knew the best way to convert this to CMOS
for my Phase Detector.

are there dedicated LVPECL to CMOS chips out there and are they expensive?

Or is there a cheaper way of doing this perhaps with a High frequency
OP-Amp?

bearing in mind that I don't care what the output looks like as long as it
crosses the CMOS thresholds.


pfitz


regards

PFitz

The newish Xilinx chips accept differential inputs, including LVPECL,
directly.

But how about this: AC couple the sig into fpga pin1, invert
internally, bring that out pin2, and feed back through a largish
resistor to the cap/pin1 node. This servoes the DC bias level, at
which point 0.8 v p-p is lots of swing.

John
 
R

raymund hofmann

Jan 1, 1970
0
Fred Bloggs said:
You're welcome to firm up that design using a single 3.3V/GND power
supply....

That would be be pfitz job.
But Before doing this, he could try to use some ready made RF
transformer for the job, as it seems to be no DC.

Raymund Hofmann
 

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