Digital Frequency/Phase Comparator (DFPC) - better than 4046 PH.C.II ?

[Glenn]

Some time ago I found this on the www:

Atmel, Digital Frequency/Phase Comparator (DFPC):
http://www.zmitac.aei.polsl.pl/Electronics_Firm_Docs/ATMEL/Atmel/acrobat/doc0475.pdf
(with circuit schematic)

Is this DFPC (using 4000 or 74HC series logic) better that the phase
comparators used in e.g. 4046, 74HC7046, 74HC9046?

4046 schematic on page 5:
http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=scha002a&fileType=pdf

When was the DFPC invented? Is it free to the DFPC for any purpose?

Glenn

 

[Gerhard Hoffmann]

Am 15.01.2013 18:38, schrieb John Larkin:

....I'd like that PFD2, too! In SC-70 !!!

4046's have a nasty deadband.

The 9046 is said to be better, but I have not used it personally.

I sometimes use an xor gate as a phase detector, or a d-flop as a bang-bang PD,
but only for narrowband (VCXO) things where pull-in range isn't a problem.

We put a nice no-deadband PFD into an FPGA now and then.

The AD9901 is a nice alternative. It moves the deadband to the
extremes of the phase range, where nobody is molested.

I recently rewrote it in VHDL, but we decided to stay with
a FLL, so it is not needed anymore.
Maybe I'll test it just for fun in a corner of a small Coolrunner..

regards, Gerhard

 

[Glenn]

On 15/01/13 22.06, Gerhard Hoffmann wrote:
....

I'd like that PFD2, too! In SC-70 !!!

....

Is there a very small cheap FPGA where a PFD2 can be implemented?

The smallest I could find at digikey and cheapest ($10 ! ) had 64 pins.

-

What about a universal 16/24/28/32square pin 74HC/74LVC/... FPGA - burn
your own (a)sync counter/PFD2/PLL/NOR/NAND/NOT/LCD-driver/... - and of
course more complicated things?

-

It is even possible to buy single gates today - example:

SN74AUC1G08DBVR - 74AUC1G08 - a dual input AND Gate:
http://www.digikey.com/product-detail/en/SN74AUC1G08DBVR/296-13170-1-ND/484304

Glenn

 

[Gerhard Hoffmann]

Am 16.01.2013 07:19, schrieb Glenn:

On 15/01/13 22.06, Gerhard Hoffmann wrote:
...
...

Is there a very small cheap FPGA where a PFD2 can be implemented?

The smallest I could find at digikey and cheapest ($10 ! ) had 64 pins.

<http://www.digikey.de/product-detail/de/XC2C64A-5VQG44C/122-1420-ND/966601>

Probably needs another SC-70 for the 1V8 core voltage.


Gerhard

 

[Allan Herriman]

Am 15.01.2013 18:38, schrieb John Larkin:

The 9046 is said to be better, but I have not used it personally.

The '9046 is definitely better. I have used it in SONET retiming PLLs.

For those not in the know, the logic in the PFD is the same as that in
the '4046, but the output is different. Instead of the hard P pullup and
N pulldown, there is a P pullup current source and an N pulldown current
sink. The currents are matched to perhaps 1% (although this is not
guaranteed in the datasheet).

The '9046 output Z is alway high, unlike that of the '4046 which is
modulated by the phase error.

Regards,
Allan

 

[[email protected]]

(snip)

You're thinking of PLDs.  You can get really old ones, on the expensive
end of the price curve, from DigiKey for $5-ish.  New, 48-pin ones are
more like $2-ish in small quantities.

a XC9536XL-10VQG44C at digikey is 1.18$ in ones

-Lasse

 

[[email protected]]

We use the 9901 in one of our ECL delay generators. It's an expensive
power hog, but we get super low jitter.

Rob, my FPGA guy, has a nice PFD design. It uses two external diodes
into a filter/opamp (my idea) so the FPGA outputs swing hard
rail-to-rail, without any tristate charge-pumpy tricks.

what would be the advantage of using diodes instead of just a tristate
output
or two ?


-Lasse

 

[rickman]

On 15/01/13 22.06, Gerhard Hoffmann wrote:
...
...

Is there a very small cheap FPGA where a PFD2 can be implemented?

The smallest I could find at digikey and cheapest ($10 ! ) had 64 pins.

-

What about a universal 16/24/28/32square pin 74HC/74LVC/... FPGA - burn
your own (a)sync counter/PFD2/PLL/NOR/NAND/NOT/LCD-driver/... - and of
course more complicated things?

-

It is even possible to buy single gates today - example:

SN74AUC1G08DBVR - 74AUC1G08 - a dual input AND Gate:
http://www.digikey.com/product-detail/en/SN74AUC1G08DBVR/296-13170-1-ND/484304

How many FFs do you want? There are some very low power devices from
Lattice that come in low pin count packages, but not so easy to use,
small pitch BGAs as small as 36 pins, 2.5 mm sq. They are targeted to
the mobile device market so they are pretty cheap, I think they are well
under $5 in quantity. iCE40xxxx, 1.2 volt core

Rick

 

[o pere o]

On 15/01/13 22.06, Gerhard Hoffmann wrote:
...
...

Is there a very small cheap FPGA where a PFD2 can be implemented?

The smallest I could find at digikey and cheapest ($10 ! ) had 64 pins.

-

What about a universal 16/24/28/32square pin 74HC/74LVC/... FPGA - burn
your own (a)sync counter/PFD2/PLL/NOR/NAND/NOT/LCD-driver/... - and of
course more complicated things?

-

It is even possible to buy single gates today - example:

SN74AUC1G08DBVR - 74AUC1G08 - a dual input AND Gate:
http://www.digikey.com/product-detail/en/SN74AUC1G08DBVR/296-13170-1-ND/484304


Glenn

If I had to do it, I would use a 44-pin CPLD (no configuration hassles)
in a PLCC package, such as Altera's EPM3064ALC44-10N for 1.78 EUR at
Digikey. I gues this is the smallest beast.

Pere

 

[[email protected]]

One is that we don't care about the subtleties (drive strength, speed)
of the tristate things. The UP and DOWN outputs each slam
rail-to-rail, fast. We control all the time constants, independent of
the silicon.

if you look at the timing spec for a xilinx cmos output the numbers
for
data-to-pad and tristate-to-pad is exactly the same, so whether you
drive
the data or the tristate pin the output transistor must be doing the
same

you get the same "slam to the rail"

More importantly, we can program a bit of overlap on the two outputs
and avoid a deadband like the 4046 type charge pumps have. The 4046
deadband can cause ghastly phase noise and jitter.

you could do the same with two outputs and no diodes

something like this:

assign pc2_p = up ? 1'b1 : 1'bz;
assign pc2_n = down ? 1'b0 : 1'bz;

-Lasse

 

[[email protected]]

Unless you are pulling up and down at the same time.

with a single high-low-tristate output that would be impossible

You'd just connect the outputs?

yes, of course if you do up and down at the same time they
will fight each other but so will two push-pull outputs with
diodes unless I missed how you'd connect them


-Lasse

 

[[email protected]]

Most of my recent PFD's have controlled current outputs.

I guess xilinx cmos outputs are also current controlled (ish)
at least they are described that way, being programmable with
2,4,6,8,12,16 or 24mA drive and fast or slow slew rate

-Lasse

 

[[email protected]]

This is one version:

https://dl.dropbox.com/u/53724080/Circuits/Phase_Detector.jpg

The resistors on the left define the currents into the integrator.

I think the diodes are redundant if you made the two outputs push/
tristate - pull/tristate
and there would be diode voltage more for the resistors to set the
current

This drives a VCXO. In non-PLL mode, we can turn on U4, turn the
integrator into a linear amp, and make the UP/DOWN signals into a
delta-sigma DAC, to open-loop tune the XO frequency.

is it really needed, wouldn't pwm/delta-sigma into the integrator work
just as good?

if it works for pll-mode it should work for non-pll mode, every thing
is the same it is just what controls the pins that changes

-Lasse

 

[josephkk]

a XC9536XL-10VQG44C at digikey is 1.18$ in ones

-Lasse

Nice. For many things i am contemplating i am looking for something like
an old 22v10. Just checked, they are still around, cool. It can do
several PFD2s and replace several packages of tiny logic at the same time.

?-)