help a novice for frequency division & duty cycle modula

[mmajid]

I need a circuit capable of producing square wave signals (0 to +5V pulses)

with some fixed frequencies like 30,20,15,10,5,1 MHZ

(the exact value of them is not so important, for example 9 ~ 11 MHZ

is acceptable instead of 10MHZ ).


I found the attached schematic on the web.the circuit produces square wave pulses

by means of a 1MHZ crystal oscillator based on 4584(IC1 in the schematic), and then

successively divides the frequency by 10 by means of a 4017(IC2~8 in the schematic),

and obtains 100k,10k,1k,100,10,1Hz square pulses.


I had tried to use this circuit for my purpose, but the problem was that the maximum

input frequency for 4584 is about 2 MHZ.


because 74HC4017 supports high frequencies( >50MHZ ),can I replace 4584 based crystal

oscillator with a single 33MHZ oscillator (DIP TTL compatible +5V oscillator) and

then feed the oscillator signal to 4017 to obtain square wave pulses whith frequcies

like 33/2, 33/3,...33/10 MHZ ?


The other problem is that 74HC4017 lowers the duty cycle of the output pulse by the

same factor that lowers the frequency.How can I turn back the duty cycle of the

output to the 50% level?
It has been mensioned on the phillips 74HC4017 datasheet (the attached paragraph)

that the output pulse withs (duty cycle) can be increased by inserting a RC circuit

on the MR input(PIN 15) of the 4017.How it can do this job, and what specifications

it must have? Can you draw the schematic of such a circuit?

On this schematic we can see that the MR pin is connected to a ouput pin.I think

that this will reset the counters successively.what will be the effect of it

on the output?

Because my knowledge of electronics is very limited, can everybody help me by very simple

terms or drawing schematics or refering to somewhwer on the web (for free schematics).

I will be very very pleased if you can help me in this way.

 

[shirazmacuff]

try to use 555 timer

Do you need all these frequencies at the same time?

If not try the famous 555-timer IC circuit
If you use the 555 timer IC you can control not only the frequency but also the duty cycle
See attachment for schematic ( I used NE 555 surface mount IC)
I have an arsenal of info on this IC. Mail me at shirazmacuff@yahoo.com for more info
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[Russlk]

The 555 doesn't operate at the high frequencies that you want, and does not output 50% duty cycle.

 

[shirazmacuff]

try using 74vhc574

Ok here goes
I’m currently working with the following IC 74vhc574mscx ssop-1 package
Why use this package?
We have to make a start sometime because the components are getting smaller every day.
The circuit divides the frequency and maintains the duty cycle
This is the actual circuit pattern that I’m using
The transistor and two resistors forms a inverter

The circuit is run at 3 HZ for testing but the IC is rated to run at 60 Mhz. note the transistor must also be high frequency if you intend to run the circuit at high frequency
The circular pattern is a rotary switch, which you use to select the output
Frequency
I cannot test the circuit at high frequency because I don’t have a scope
I also notice that if I tie all the outputs to ground with a 20k resistor the performance improves. I also tied the base of the transistor with a 10 k resistor to ground

Does anyone know how I can test this circuit at high frequency without having to build a multiple units?
If anyone could improve please do.