[time-nuts] time-nuts Frequency Divider

Richard H McCorkle mccorkle at ptialaska.net
Sat Apr 4 19:20:40 UTC 2009


The specifications for AC coupled input sensitivity of the 74HC4046
from the major manufacturers are shown below. Brooks found that the
Fairchild device had lower sensitivity and recommended using devices
from TI or Phillips.

Fairchild MM74HC4046
Ac coupled input sensitivity @ 500 KHz

 25mv p-p typical, 100mv p-p guaranteed at 25C @ 2v
 50mv p-p typical, 150mv p-p guaranteed at 25C @ 4.5v
135mv p-p typical, 250mv p-p guaranteed at 25C @ 6v

Phillips 74HC4046A, TI CD74HC4046
Ac coupled input sensitivity @ 1 MHz

 9mv p-p typical @ 2v
11mv p-p typical @ 3v
15mv p-p typical @ 4.5v
33mv p-p typical @ 6v

On Semiconductor MC74HC4046A
Ac coupled input sensitivity not specified


> Ulrich Bangert said the following on 04/04/2009 06:13 AM:
>>> As a curiosity, there are various variants of the original 4046 which
>>> has different sensitivity on the input side... one of them
>>> has several inverters in a row to get the needed gain where as the other
>> variant
>>> does not. This difference made a huge difference in some applications.
>> are you going to say with that it would be reasonable to test different
>> brands for input sensivity? I have been believing that all brands have this
>> inverter chain.
> Brooks Shera used the 4046 as the input conditioning circuit in his
> GPSDO that was published quite a while ago.  I seem to recall that he
> noted only certain brands seemed to work well, but I don't recall the
> details.
> John
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