frequency divider problem

[paul0]

Hi all,

I have a problem using my frequency dividers :

1) the frequency divider consist of a schmitt trigger, filtering capacitors, and a flipflop(HC74)
2) the dividers are connected as described in the figure below : Common Vdd, Common Gnd from power supply 3.3V 6A

problem
1) When I use a single power supply for the 3 dividers the required division precision is totally lost only 1 measure on 3 works ( Note that the maximum current of the power supply is 6A at 3.3V)
2) When I use separated power supply for each dividerI got my measures and all the 3 circuits works well






What I suspect
1) there may be a noise coming from the ground of the frequency meter or the mux ??
2) I should (may be) connect some pull down resistor at the output of each divider ??


If anyone have some ideas I will really appreciate,
Thank you for help

 

[chuckey]

Have you connected a decoupling capacitor across each chip?
Frank

 

[paul0]

Have you connected a decoupling capacitor across each chip?
Frank

Thanks Frank

if you are talking about decouplig capacitors inside the divisor, yes there are some .
But the mux is the agilent 34901a so I think that we do not need decoupling capacitor in front (inside the 34901a there are some relays )
Do you think that I need to add decoupling capacitor in front of the mux ???? do you think about some feedback current ????

thanks

 

[paul0]

Hi

I had measured about 20mA of ground current that may cause the problem !!!

thanks

 

[iop95]

Add capacitors decupling, 1x0.1microF + 1x100microF.