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High Frequency Square Wave Division Duty Cycle Adjust

Kenneth Hamersma
Prodigy 20 points
Other Parts Discussed in Thread: SN74LS292, SN74ACT74

Hello to all,   My name is Ken and I am a first time poster and terrible typer so I apologize for that.

My project is as follows, Sine wave input 30mhz / Square Wave Output  30mhz or 60mhz depending on choice for frequency division or not to achieve a dual output 30mhz per output with duty cycle adjustments on each output.  I was looking at using a pair of 74act74 devices to divide my 60mhz trigger and provide my duty cycle adjustments.

I am currently using LtSpice which is all I have. The devices from LT have got me to the 60mhz clock output and now my question is what device from TI, D flip flop or otherwise would be a good choice from here. Any Help is appreciated.

Ken

  • 0
    TI__Guru 58790 points
    Hi Ken ,

    A conversion from sine wave to square wave would require a Schmitt trigger which can tolerate slow rising edge signals and trigger the device at the threshold point to generate a square wave . Also ,using a D flip flop with input frequency at 60Mhz and having the Q\ output tied back to its D input would result in output frequency of 30Mhz . further division is possible with cascading the flipflops.
  • 0 in reply to ShreyasRao
    TI__Guru 58790 points
    Hi Ken,

    Apart from using the D flipflops, you can also look into using the SN74LS292/4 programmable freq dividers and timers.
  • 0 in reply to ShreyasRao
    Prodigy 20 points
    Hi Shreyas,

    Thank you for the reply, at this time using Ltspice and components within LT I have my conversion and doubling completed.
    my main concern at the 60mhz clock input using a SN74ACT74N would be sufficient at that frequency.
    Looking at the datasheet it is questionable. Do you have a recommendation otherwise? Only adding to the project complexity it must be frequency agile and duty cycle adjustable the duty cycle adjustments I have already figured out using 2 SN74ACT74N Flip Flops but have no way of testing them in Ltspice can you help me there I have no model and i am a new user of Ltspice and conversions are difficult. Thank You again and I will look at the SN74LS292?4 datasheet

    Ken
  • 0 in reply to Kenneth Hamersma
    TI__Guru 58790 points

    Going by the frequency spec , the SN74ACT74 should be able to handle 60Mhz well .The max clock frequency is around 125Mhz . There are other flip flops with higher frequency ratings . I have filtered them here .