Fastest counter?

[eromlignod]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

Thanks for any replies.

Don

 

[Don Lancaster]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

Thanks for any replies.

Don

And the problem with prescaling your input is...?


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
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[eromlignod]

And the problem with prescaling your input is...?

I'm measuring the period of another wave by counting how many cycles of
a 10 MHz oscillator occur during one cycle of the measured wave. 10
MHz doesn't quite give me the desired resolution for sufficient
accuracy in my application.

Don

 

[RobJ]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

Thanks for any replies.

Don

You could easily count at > 100MHz in a CPLD or FPGA depending on how many
bits in the counter. The parts are pretty cheap and the development tools
are free.

Rob

 

[Joerg]

Hello Don,

I'm measuring the period of another wave by counting how many cycles of
a 10 MHz oscillator occur during one cycle of the measured wave. 10
MHz doesn't quite give me the desired resolution for sufficient
accuracy in my application.

Then that only leaves the solution Rob hinted: Use an external device,
FPGA, fast counter plus serial readout, whatever. You could also take a
look at ARM processors with higher clock speeds and at DSP. Some might
offer timers that can be clocked higher.

But are you sure your clock oscillator is up to snuff WRT to your
precision goals? To maintain a 10MHz clock to within 1 Hertz for any
length of time is no small feat. Think about big, oven-stabilized, no
vehicle traffic, no sneezing within 100ft and so on. You'd almost have
to lock that to WWV and even then short term propagation jitters can
throw you a curve.

Even if it's a Doppler application some of the above still applies.

 

[eromlignod]

Hello Don,
Then that only leaves the solution Rob hinted: Use an external device,
FPGA, fast counter plus serial readout, whatever. You could also take a
look at ARM processors with higher clock speeds and at DSP. Some might
offer timers that can be clocked higher.

But are you sure your clock oscillator is up to snuff WRT to your
precision goals? To maintain a 10MHz clock to within 1 Hertz for any
length of time is no small feat. Think about big, oven-stabilized, no
vehicle traffic, no sneezing within 100ft and so on. You'd almost have
to lock that to WWV and even then short term propagation jitters can
throw you a curve.

Even if it's a Doppler application some of the above still applies.

I've been getting good results from a little OCXO. I think it's good
to about 0.5 ppb or so. Thanks for the advice.

Don

 

[Ancient_Hacker]

I'm measuring the period of another wave by counting how many cycles of
a 10 MHz oscillator occur during one cycle of the measured wave. 10
MHz doesn't quite give me the desired resolution for sufficient
accuracy in my application.

Don

How about trying Don's idea: Put a 1/256 divider on your input.
Assuming you have 256 cycles available, your measurement error goes
down by 256 times.

 

[Joerg]

Hello Don,

I've been getting good results from a little OCXO. I think it's good
to about 0.5 ppb or so. Thanks for the advice.

Those are nice. But their tolerances are typically much higher than
that. For example the Connor-Winfield Stratum 3 series (IIRC around $100
a pop) are over 4ppm in max tolerance. Aging alone can be 30ppb, per day.

 

[Spehro Pefhany]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

Thanks for any replies.

Don

I'd be surprised if the external counter input(s) on micros such as
the PIC24H (made in 0.25u process) wouldn't count at >>100MHz
typically. Older parts such as the 18F4550 will count at 50MHz
guaranteed over temperature.


Best regards,
Spehro Pefhany

 

[eromlignod]

Ancient_Hacker wrote:
How about trying Don's idea: Put a 1/256 divider on your input.

Assuming you have 256 cycles available, your measurement error goes
down by 256 times.

I guess I don't understand what you guys mean. If my measured signal
is, say, 5000 Hz and I divide it by 256 then I get 19 plus a remainder.
Wouldn't that round-off error destroy my accuracy, or maybe I'm not
understanding what you propose?

Don

 

[Luhan]

I'd be surprised if the external counter input(s) on micros such as
the PIC24H (made in 0.25u process) wouldn't count at >>100MHz
typically. Older parts such as the 18F4550 will count at 50MHz
guaranteed over temperature.

I get 50mhz out of an ordinary PIC16F870. Just totally replace the
82C54. Probably cheaper too.

http://members.cox.net/berniekm/super.html

Luhan

 

[Joerg]

Hello Don,

I'm measuring the period of another wave by counting how many cycles of
a 10 MHz oscillator occur during one cycle of the measured wave. 10
MHz doesn't quite give me the desired resolution for sufficient
accuracy in my application.

There is another trick if you still have a few port pins available: Get
two fast four-bit counters, a fast four-bit or wider latch and a really,
really good OCXO for 160MHz (that one is going to set you back a pretty
penny). Use one counter to divide the 160MHz by 16 and feed that to the
uC, or whatever clock it needs, but this must be synchronous to the
clock of the 2nd counter.

Use the other counter and latch its value every time the timer finishes.
Run the timer input off the tail which will be 10MHz pulses. Read in
the latched values through four port pins. Those will now be your new
least significant bits. If you are hard pressed for port pins you could
serialize that.

 

[Joerg]

Hello Don,

Ancient_Hacker wrote:
How about trying Don's idea: Put a 1/256 divider on your input.


I guess I don't understand what you guys mean. If my measured signal
is, say, 5000 Hz and I divide it by 256 then I get 19 plus a remainder.
Wouldn't that round-off error destroy my accuracy, or maybe I'm not
understanding what you propose?

He meant measuring it 256 times in a row and calculate the average from
those 256 runs. Doesn't work for non-repetitive events though.

 

[qrk]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

Thanks for any replies.

Don

My colleague just got done making a counter with 2.5 ns resolution
using a Spartan 3 FPGA.

 

[eromlignod]

Hello Don,
He meant measuring it 256 times in a row and calculate the average from
those 256 runs. Doesn't work for non-repetitive events though.

Oh, I see. The problem is that the reason I picked this method in the
first place is because I can get a fast reading. Otherwise I would be
frequency-counting. I currently measure over 200 different waves by
polling them all over and over and it takes about one or two seconds
per pass. I can't wait a long time for each measurment since I'm
constantly making adjustments based on this feedback.

Don

 

[Rene Tschaggelar]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

I used an FPGA to build a 28bit synchroneous
counter running at 120MHz.
Then I also have an MC100EP016A, a synchroneous
8 bit counter doing 1300MHz

Rene

 

[Joerg]

Hello Rene,

Then I also have an MC100EP016A, a synchroneous
8 bit counter doing 1300MHz

Now we're talkin'...

 

[[email protected]]

Hello Rene,

And you can string them together to get a synchronous counter of
essentially unlimited width capable of at least 500MHz - I could get
that out of the MC100E016.

Putting proper 50R to -2V terminations on every single-ended counter
output can introduce enough noise on the power rails to prevent the
counter working at ful speed.

Higher resistance terminating resistors don't damp transmission lines
nearly as fast, but if you can afford to waiit for a few nanoseconds
after stoppping counting, the outputs will have time to settle.

 

[Fred Bloggs]

Oh, I see. The problem is that the reason I picked this method in the
first place is because I can get a fast reading. Otherwise I would be
frequency-counting. I currently measure over 200 different waves by
polling them all over and over and it takes about one or two seconds
per pass. I can't wait a long time for each measurment since I'm
constantly making adjustments based on this feedback.

Just take something like the 74VHC163 a 4-bit 180MHz counter and use the
terminal count to ripple clock your 10MHz 82xx thing. At 100MHz, the
82xx only sees 100/16=6.25MHz. You don't need every little stage to have
100MHz capability. There might be the slightest little challenge of
stretching the high speed terminal count to satisfy the minimum clock
width requirements of the 82xx- but that's what engineers are for.

 

[James T. White]

Hi guys:

I'm currently using an Intel 82C54 programmable timer/counter in an
application. I'm using the version that can count up to 10 MHz.

It's looking like I might need to count even faster than that. Are
there other counter chips, or even processors, that can count faster
than 10 MHz? 100 MHz or more would be nice.

Try
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