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sine to square circuit

zohar livny
Prodigy 10 points

Other Parts Discussed in Thread: LMV7219, LMK00105

hello,

i have come across a reply given by mr alan ocampo concerning the use of the LMV7219 comparator as a sine to square converter for a 10 mhz signal.

also, included was a formula for calculating the input jitter dependence on the slewing rate and the hysteresis.

i have an application for an input signal at 100mhz.

i have the following questions:

1 can i use the LMV7219?

2 what would be the current consumption at 100mhz 5v and 8 pf load?

3 the above mentioned formula for the jitter is counter my intuition, can an more elaborate explanation be given?

thank you in advance

zohar livny

  • 0
    TI__Mastermind 32575 points

    Hi Zohar,

    A1: Based on 1.3 ns output edge time at 5 V supply, it should be able to support 100 MHz toggle rate.  But you should verify this on an evaluation board to ensure it meets your requirements. For high speed CMOS clock buffer/level translator, you may also consider LMK00105 fanout buffer. 

    A2: Ptotal = Pstatic + Pdyn = Is*Vcc + Cload*Freq*Vcc^2 = 2.4mA*5V + 8pF*100Mhz*(5V)^2 = 32 mW @ max static supply current over temp

    A3: The sinusoidal input frequency determines its slew rate which affects how fast the signal passes through the comparator's trigger threshold.  If there is a fixed amount of thermal noise on the internal input stage of the comparator, then the slew rate gets converted into timing uncertainty, which degrades the inherent additive jitter of the Comparator (broadband noise floor increases as input slew rate decreases).  This slew rate impact can be observed on any device that has a comparator switching threshold, such as ADC clock inputs, clock buffers, etc. In fact, the LMK00105 datasheet shows typical plots of how its output RMS jitter and phase noise floor degrade at lower input slew rates. 

    Regards,

    Alan