Ahhh, the beauty of the 74xx90 is that you can have a symetrical output
by using the divide by two after the divide by five.
Max
On 4/01/2013 1:02 PM, Tom Miller wrote:
Isn't there a fast divide by N counter that you could set to 10? Maybe
even in ECL?
----- Original Message ----- From: "David" <davidwh...@gmail.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Thursday, January 03, 2013 8:49 PM
Subject: Re: [time-nuts] 10 MHz -> 16 MHz clock multiplier
They do not exist as I found out (again) not long ago. The last 7490
made was LS (low power schottky) and I use quite a few of them.
Actually, I have seen a datasheet for a 74HC90 and 74HCT90 but they
apparently either never went into production or very few were
produced.
The closest non-TTL alternative that I found was the 74HC390 or
74HCT390 which is basically two 7490 counters in one package.
On Fri, 04 Jan 2013 11:59:01 +1100, Max <vk3...@gmail.com> wrote:
Where can one get some of these mythical 74HC90 's and 74AC90 's that
have been mentioned.
None of the usual places have them, ie ebay, digi-key, farnell, or
even the Chinese.
Also data-sheets are not to be found.
Thanks
On 4/01/2013 5:13 AM, Bill Fuqua wrote:
One way is to divide by 10 and then multiply by 16.
Divide by 10 and then follow by 4 tuned frequency doublers.
This should introduce little phase noise.
Another way to do it is to divide by 10, then pass the output
thru a
narrow 16 MHz filter and amplify. Sounds difficult but the filter can
be one
or two 16 MHz crystals followed by a simple amplifier. Look at the
reference input circuit for a PTS-160. The output of the divide by 10
needs to
be asymmetrical so it produces even harmonics. If you are using a
divide divide by 5&2 such as a 74HC90, divide by 2 first then by 5.
Ideally the pulse width should be a half period of 16 MHz for the
maximum harmonic content at 16 MHz.
You can take the output of the frequency divider and send it to a
NAND gate.
One input of the gate is directly connected and the other is delayed.
You can
use an RC with a variable capacitor to ground to get it just right.
Just adjust the capacitor to get the maximum output from your
filter amplifier.
73
Bill wa4lav
At 07:41 PM 1/2/2013 +0000, you wrote:
What's the simplest way to generate 16 MHz from 10 MHz? This will be
for clocking a microcontroller at 16 MHz given 10 MHz (Cs/Rb/GPSDO).
Low price and low parts count is a goal; jitter is not a concern but
absolute long-term phase coherence is a must.
The ICS525 (as in TAPR Clock-Block) is a good candidate but I was
wondering if there's something cheaper, less functional, and maybe
not SSOP. Any suggestions?
Thanks,
/tvb
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