Monoshot multivibrator triggering

The Qbar outputs should start out high at power up.

Yes

So what kind of ckt should i use for generating trigger pulse.

1) Can I rc delay ckt from supply vtg,so that it will edge trigger after turning on.But trigger pulse is mentioned 140ns(min) in datasheet.

2) Should i used a differentiator ckt for producing spikes for edge trigger. But this spike will be able to trigger the  output.

You can use the Rc delay and then use a single gate schmitt trigger to increase the rise time to meet spec.

But pulse width is 140ns.Is there any problem my input pulse width after rc delay will remain continuous high state.

Any other idea for generating pulse so plz share.

The part is edge triggered so all you need is an edge. The minimum pulse width just means you cannot have a pulse less then the limit or the part might not see it.  

It means trigger input pulse width is independent of output pulse width .It can be more than it also.Fine

That is correct

What Schmitt trigger gate i should use...buffer or inverter after RC .

In CD4098B ,trigger prpagation delay Tphl= 250ns and trigger pulse width Twh=70ns for 5V VDD.

Which Schmitt trigger gate will meet this???

RC delay ckt for triggering is not working...is der any other to generate single pulse.

You could try the SN74LV123A. It is a 5V part. and will have schmitt trigger inputs on the trigger pins 

I am using DM 54121 which is similar to SN74LV123A has trigger inputs A1,A2 and B.I am trying to trigger B input as mentioned in datasheet.

I tried with RC delay at B input it saturates at voltage 5V and with differentiator it saturates at 2V. At B input,Positive-Going Input Threshold is 2V(max) and negative-going input threshold is 1.3V(max).But they are not able to trigger the monoshot. What this trigger threshold voltage means and how can trigger the monoshot.

With a differentiator ckt ,it is getting trigerred but with other delayed input.If I connect RC delay before differentiator that capacitor of RC is holding 5V and its not able to trigger it.