Signal Generator Clock Pulse Issue

[JonPyro]

Hi All,

I am trying to construct a test rig that will send clock pulses to some boards that have a 4013B flip flop wired as a latch. Rather than directly connect the output of a signal generator to the clock input I thought it would be fun just to add some extra complications and drive the clock pulse from a mosfet instead and drive the gate with my signal generator (Rigol DG822).

This is the circuit:



For my reference I have an LED also on the source so I can visually see the clock pulses get sent, however, an interesting thing happens.

My signal generator is set up sending a PWM of 1hz and duty cycle of 10%:

probed at the mosfet source:




You will notice the first pulse is when I enable my sign gen output, you can see the rise time is much longer than the other pulses, here is the first pulse on its own:




Here is the second and beyond pulse:





This long first pulse is causing the 4013bs to go wobbly as its a invalid clock rise time but why does only the first pulse do this?

I have connected my sig gen directly to my scope input and every pulse is perfect, so it must be my circuit to blame but I am not sure why.

Any help would be appreciated.

[radiolistener]

did you tried to remove LED to avoid output distortions?

[JonPyro]

I have tried removing the 4013 boards and the led and it still has a slow rise on the first pulse. Interesting when I remove the led the waveform shows more overshoot and undershoot on the over pulses but the first is still slow.