Using a counter as a frequency divider

Hi all,

i am looking for a programmable chip that can divide from 1 until 50 and preferrable until 250. It must be able to take a 100Mhz signal at its input and preferably up to 500Mhz. Can anyone guide me on finding a chip like this. The input/output signal should be either TTL or ECL. I have searched with no luck in what i need. I want one that is simple to use. where u put the input signal into the ic, program it the amount to divide by and get the output signal.

J

frequency divider

You could use an FPGA. Otherwise I think On Semi make the fastest, readily available logic chips with their MC100 range:

https://www.onsemi.com/PowerSolutio...Filters=Y&searchType=others&lctn=headerSearch

Keith.

frequency divider

Hi,
ECLinPs Light Chips are faster ("Tyni function PECL" vomponents ie in SO8 packages), originally from ON Semi, but has second sources & Low Voltage versions too...
The "normal ECLinPs family" has programmable counter up to(I remember so) ca 1.3Ghz.
K.

Re: frequency divider

hi, i am glad for your reply. Tell me, how does one use a counter as a divider. i am a bit confused now because when i look for dividers sometimes counters come up. i am not sure i understand the difference. can i use a counter as a frequency divider and how?

frequency divider

A counter and divider are really the same thing - a chain of flip-flops. They get the different name from how they are used.

If you feed your high frequency signal into the clock of a counter then the counter bits will have half, quarter, eighth frequency outputs etc.

Keith.

Re: frequency divider

that is awesome, because i have a counter that can take 100mhz at its input, my problem is i never understood the whole timing diagram on the datasheet. maybe you can help me. i am trying to use the 74f269, but what i dont get is, there are 8 data input pins, as i understand it i have to pass 8 bits to the chip to tell it how much to divide by. like 0000 0010 would divide by 2. but what i dont get is the Q outputs, why are there so many? surely if im dividing by one number only there should be only one output? what dont i understand? what am i then actually setting with the data inputs.

pplease try to help me understand how i can get this ic to work as i need it, because i dont understand the timing diagram.

frequency divider

It's a presetable up/down counter although I am not sure if its the best way of doing a programmable divider (I am an analogue engineer). The most useful page for understanding the pins is Table 2 (assuming you are looking at the NXP data sheet) www.nxp.com/documents/data_sheet/74F269.pdf where the pins are described.

So, yes, you could preset the counter with a number and make it divide up or down from there and when it reaches the terminal count, load it again. Your count output would be the terminal count, but it would be a blip. The Q pins will change as it counts along the way. You could use those to get your output but the mark space ratio wouldn't be 50:50 and you need to pick the right pin. For example, if you wanted to divide by 10 and you were counting down, you could pick D3 as your output. That would be high for a couple of clocks and then stay low for the next 8 while the counter continues to count down until it reaches zero.

As I say, I am really an analogue engineer - you need a digital one really! I use CPLDs, micros and logic only when absolutely necessary.

Keith

Re: frequency divider

So do i use it as follows: i set the U/D pin to high to count up. CEP,CET and PE must be grounded. then i connect a PIC to the data input pins, and set them depending on the amount i want to divide by. my signal will be put through the CP pin and the divided signal will be at the TC pin? is this correct? also, how will i then know when i need to reload the chip?

i am also not sure if i should make a divider in this way, that is why i was looking for a proper dividers, but when i search the sites, including the one u gave me just now, it seems as if they only divide until like 32, unless im not informed on how to use them otherwise.

frequency divider

Hi,
by your counter if its finished> TC* will go to Hi, than you have reload (controlled from that) the counter for repeating the job...
K.

frequency divider

You need to reload in less than one clock cycle. It needs to be done with fast logic.

Keith.

Re: frequency divider

You probably want this divider:
https://www.onsemi.com/pub_link/Collateral/MC100EP016A-D.PDF

You MIGHT be able to find a single chip cmos divider somewhere, like using a UHF PLL chip from analog devices, ignoring the PLL part, and just using the test pins to get at the programmable counter part. Unfortunately, these "dual modulus" counters typically have gaps in the divide by N integer, so you might not get the full number of different divisors you are looking for.

Rich

frequency divider

Hi Rich,
Exactly, that was what I wished to suggest
I built a synthesizer at 1GHz with that so 16 years ago_it was & is a nice ECLinPs counter...
K.

Re: frequency divider

Hi all, i would like to know if an external buffer is still needed before putting the signal through the counter? because i know that u need a buffered probe in order to see the signal on an oscilloscope,

frequency divider

Hi,
Input side is surly depending from driving power of your source...
On the outputs, I dont believe that you must the (high imp.)scope probe buffern.
ECL/PECL Outputs delivers currents in high of tenth milliamps, a probe makes maximum some capacitance load to that, but their ICs are specified with a load C=50pF, if I remember correctly on value...
Use it pls as PECL (Positive ECL) & than you can load it directly to GND with 50 Ohm too ...
K.

Re: frequency divider

sorry but i don't understand what you are trying to say. All i need to know is whether i need a buffer between my oscillator and the counter?

frequency divider

Aha;
You must know how high your signal is...
Maybe you must amplify it, but relative sur is; that you must shift it to the thresold of your counter.
K.