[time-nuts] 10 MHz -> 16 MHz clock multiplier

David davidwhess at gmail.com
Fri Jan 4 01:49:32 UTC 2013


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 <vk3yba at 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
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to 
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>_______________________________________________
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.



More information about the time-nuts mailing list