Freq divider by 4?

[electroRF]

Hi,
I was reading this slide, and saw how they divide frequency by 4, which seems wrong to me.

Why did they connect Q1' with Q0'?

Does that make sense to you?

(Slide is from https://www.slideshare.net/DeepakFloria/divide-by-n-clock)

Thank you.

 

[MikeMl]

No, just more crap posted on the internet by some "expert". Leave out the wire from Q0' to d0, and it becomes a Gray code counter with four states which will divide by four.

 

[Ian Rogers]

Er!!! No the second D type should be clocked by the first.. The way they have it Q1', Q0' and D0 will fry!!

 

[geko]

Probably because they cut-and-pasted the divide by 2 D-FF from 3 slides previous and forgot to remove the line.

 

[MikeMl]

Er!!! No the second D type should be clocked by the first.. The way they have it Q1', Q0' and D0 will fry!!

No, if you do it like I said, it is a synchronous counter with the external clock going to both Clk inputs. The way Ian suggests turns it into a ripple counter, with its usual hazard problems.

 

[Ian Rogers]

No, if you do it like I said, it is a synchronous counter with the external clock going to both Clk inputs. The way Ian suggests turns it into a ripple counter, with its usual hazard problems.

I tried it your way, I doesn't divide by four.... The ripple counter does.... Anywho the OP was right!!! doesn't work as shown!!

Opps!! Sorry Mike you are correct.... Just tried it again...

 

[MikeMl]

As you can see in the sim above, the Gray Code counter counts 01320132... The two outputs are in phase quadrature.

 

[electroRF]

Guys,
Thanks a lot!

Do you know good guide for how to design a frequency divider using FFs?

I found just this https://www.scribd.com/doc/13305418/Building-Dividers-With-Flipflop

and it doesn't expalin things that well.

 

[MikeMl]

A "divider" is nothing but a counter. A counter is just a state machine. I learned how to design state machines long before I even heard of dividers. Your reference just muddies the water by talking about designing dividers as though it is a whole new discipline...