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LM339: Looking for high speed (>200MHz) pulse generator

Hua Chen
Prodigy 100 points
Part Number: LM339
Other Parts Discussed in Thread: TLV3601, TLV3801, SN74LV1T00, SN74AUP1T57, SN74AUP1T34, TLV3603, SN74LVC1GU04

Tool/software:

Hello, TI experts,

currently looking for a very high speed(>200MHz) sonusoid to square waveform signal generator IC or similar product(like a pulse generator). I would to convert signal generator high speed sine waveform output to s square waveforms as an input on PCB. Sounds like LM339 may do the work, could you provide details schematic/diagram show how to realize or do you have spice model for it? 

thanks, 

Harris

  • 0
    TI__Guru 52236 points

    Hello Hua,

    The LM339 would never pass 200MHz. It tops out at about 1MHz - if you are lucky.

    You will need a high-speed comparator, with a speed faster then ~2.5ns to get a clean output. The faster the better.

    What is your input signal level, and what output level are you expecting?

    I will warn you as you get into the nanosecond range, the edge rates are so fast that most of the comparators will have LVDS or some sort of reduced output swing. You will NOT find anything that will swing greater than 5V at that speed.

    I would first look at the TLV3601 as a start. That has a standard Push-Pull output. The TLV3801 family has LVDS outputs.

  • 0
    Guru 267140 points

    At 200 MHz, the pulse length is 2.5 ns. The LM339 has a propagation delay of 1300 ns. You need a high-speed comparator like the TLV3601.

  • 0
    Prodigy 100 points

    Hello, 

    I checked withTLV3601 and its family. I agree I need a high-speed comparator (as a buffer) like this. But, TLV3XXX family does not have Schmidt trigger feature, so I can see output could switch up and down very fast during the transition. Then, I found a pspice model for SN74LV1T00 which has a good function for what what I'm looking for. However, input sinusoid frequency is only up to 120MHz(hope to acheive 200MHz), and VCC can only go up to 3.8V(hope to achieve 5V VCC). Can I find a comparator with schmidt trigger, also get higher input frequency range and wider VCC range? I found SN74AUP1T34 and SN74AUP1T57. they both have higher frequency, but VCC could be limited, and I cannot find PSPICE model. can you provide unpublished or soon-to-be-released PSPICE model for them? Or could you recommend other similar IC with PSPICE? 

    Best

  • +1 in reply to Hua Chen
    TI__Guru 52236 points

    Hi Hua,

    "Schmidt Trigger" = Hysteresis. The "Schmidt" trigger logic gates add internal hysteresis. Hysteresis is the difference between the upper and lower thresholds. The logic gates looks to have 100-300mV of hysteresis.

    The high speed comparators have a small amount (3mV) of internal hysteresis to prevent "chatter" (up-down). It is also possible to add external hysteresis if needed. So the comparator would have more accurate trip points (±1.5mV of the set threshold). That makes for more symmetrical output if the threshold (reference) is exactly in the middle of the sinewave.

    The TLV3601 can go up to 5V - that is your best bet. The TLV380x is 4.2V max. Higher speeds require smaller devices, and smaller devices have lower breakdowns - so the supply voltage is reduced.

    Again, what is the input (VOH and VOL) of the input sinewave? What output levels do you need? 5V is going to be difficult to get cleanly.

  • 0 in reply to Paul Grohe
    TI__Guru 52236 points

    Oops.. I meant ±1.5mV - not 1.5V.

  • 0
    Prodigy 100 points

    Hi, 

    The found TLV3603 can offer the function I need. Just curious... Can I use the two small, fast invertors to build high speed buffer circuit? I guess that could work as well?  can you suggest the small, high speed invertor or small, high speed buffer IC? 

    Input VIH=5/5.5V, VIL=0V, VOH=5/5.5V, VOL=0V.  I would like the simulate for all three cases at 100MHz, 150MHz, and 200MHz.   

    thanks,

  • 0 in reply to Hua Chen
    Guru 267140 points

    There are fast buffers, but the fastest logic family, AUC, does not work above 2.5 V.

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    hello, Clemens,

    So, does TI have 5V MOSFET high speed logic simple Invertors(1N+1P) or Buffer(2N+2P)? thanks

  • +1 in reply to Hua Chen
    Guru 267140 points

    The fastest 5 V logic family is LVC. The SN74LVC1GU04 is an unbuffered inverter, but its worst-case propagation delay still is 3 ns or more.

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    SN74LVCGU04 seems to be the same as SN74LVCG04.(The pspice models are the same). Looks like, the LTSPICE can read this model. I would like to simulate it with cadence virtuoso, but Iooks to me, cadence tool cannot read some syntax (such as subcircuit and math functions). I remember the gate drive LMG12XX famliy pspice or spectre model works with cadence. how come this one cannot? can you provide a cadence compatible spice model for SN74LVCGU04?   thanks!

  • +1 in reply to Hua Chen
    TI__Expert 3590 points

    Hi Hua,

    Could you make a new post with the SN74LVCG04 such that the responsible team could get back to you about the modeling? 

    Thanks,

    Ho