Frequency Divider - a circuit with specified output

[Monady]

Frequency Divider

Hi dear all friends,
I need a frequency divider, I used of Johnson counter but this circuit couldn’t obtain my requirements. For example in Johnson counter with 4 D-FF, Output is Vdd for 1*Ts and 0 for 7*Ts. But I need a circuit which its output be Vdd for 0.5*Ts and 0 for 7.5*Ts.

Your help will be appreciated

 

[Kral]

Re: Frequency Divider

Monady,
If your clock is symmetrical (50% duty cycle), then you can use a frequency doubler to obtain a clock that is double the frequency of the original clock. See **broken link removed**. You don't need to use a delay line. You can use an RC low pass followed by a Schmitt Trigger.
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Use this clock as the input to an 8 stage Johnson counter. Decode states 0 and 8 to get the desired output.
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A word of caution about the Johnson counter. If it ever gets into an invalid sequence, it will never get out without some extra logic to detect the invlid states a force the counter into a valid state.
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Regards,
Kral

 

[Monady]

Frequency Divider

Dear Karl Thx for your reply.
first of all i should say it that i use of this block in my circuit and i must design all parts of it(Transistor level), thus i can't use of any Schmitt Trigger IC.besides i think that mentioned circuit can't solve my problem.desired output attached, may be i couldn't explain it well.

 

[Kral]

Re: Frequency Divider

Monady,
I see what you're trying to do. Can you just logically "And" your Johnson counter output with the clock?
Regards,
Kral