help with 120MHz comparator

[Ted Lechman]

I'm trying to convert a 120MHZ 1V p-p ac coupled sinewave to a LVTTL
(3.3V) format for use as a 120MHz clock signal to an FPGA.
1. PECL Comparator - I'm trying to avoid using PECL Comparators,
because I would have to convert the PECL output to a LVTTL swing,
which just brings me back around to the original problem.
2. "normal" comparators - I've looked through Linear Tech and other
places, and the max spec is 100MHz. Do you know of any LVTTL
comparators with specs closer to 120MHZ??????????
3. Transistor. There are many high frequency RF transistor with
excellent small signal gains around their bias points but lousy large
signal - DO you know of any discrete transistors that will switch
fully at 120MHz rates??
Thanks

 

[Daniel Lang]

I would recommend a LVDS receiver to convert your sinewave to
a LVTTL signal. Use 2 resistors and a capacitor to bias one
input at 1.2 volts and run a terminating resistor to the other
input.

You could also feed the signal directly to the FPGA if it has
a LVDS clock input although this will give more jitter.

Daniel Lang

"Ted Lechman" <eastwood132@yahoo.com> wrote in message
news:b89924f9.0311041104.69d352b5@posting.google.com...

I'm trying to convert a 120MHZ 1V p-p ac coupled sinewave to a LVTTL
(3.3V) format for use as a 120MHz clock signal to an FPGA.
1. PECL Comparator - I'm trying to avoid using PECL Comparators,
because I would have to convert the PECL output to a LVTTL swing,
which just brings me back around to the original problem.
2. "normal" comparators - I've looked through Linear Tech and other
places, and the max spec is 100MHz. Do you know of any LVTTL
comparators with specs closer to 120MHZ??????????
3. Transistor. There are many high frequency RF transistor with
excellent small signal gains around their bias points but lousy large
signal - DO you know of any discrete transistors that will switch
fully at 120MHz rates??
Thanks

 

[Hal Murray]

I'm trying to convert a 120MHZ 1V p-p ac coupled sinewave to a LVTTL
(3.3V) format for use as a 120MHz clock signal to an FPGA.

1. PECL Comparator - I'm trying to avoid using PECL Comparators,
because I would have to convert the PECL output to a LVTTL swing,
which just brings me back around to the original problem.

I got burned (years ago) using a PECL-TTL level shifter. It had
a normal TTL output when I wanted a CMOS signal. Worked much better
when we added a CMOS gate/buffer to clean it up.



I'd probably try a fast CMOS inverter. AC couple your signal in
and feed a 1 megohm resistor from the output back to bias the
input. Got a couple spare pins on your FPGA?



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[Austin Lesea]

Daniel,

Of, if it is has an SSTL or HSTL or GTL input (which has a reference
voltage) you have the high speed comparator already built in to your FPGA.

Austin

Daniel Lang wrote:

I would recommend a LVDS receiver to convert your sinewave to
a LVTTL signal. Use 2 resistors and a capacitor to bias one
input at 1.2 volts and run a terminating resistor to the other
input.

You could also feed the signal directly to the FPGA if it has
a LVDS clock input although this will give more jitter.

Daniel Lang

"Ted Lechman" <eastwood132@yahoo.com> wrote in message
news:b89924f9.0311041104.69d352b5@posting.google.com...
I'm trying to convert a 120MHZ 1V p-p ac coupled sinewave to a LVTTL
(3.3V) format for use as a 120MHz clock signal to an FPGA.
1. PECL Comparator - I'm trying to avoid using PECL Comparators,
because I would have to convert the PECL output to a LVTTL swing,
which just brings me back around to the original problem.
2. "normal" comparators - I've looked through Linear Tech and other
places, and the max spec is 100MHz. Do you know of any LVTTL
comparators with specs closer to 120MHZ??????????
3. Transistor. There are many high frequency RF transistor with
excellent small signal gains around their bias points but lousy large
signal - DO you know of any discrete transistors that will switch
fully at 120MHz rates??
Thanks