4 Replies Latest reply on Sep 14, 2012 10:52 AM by weston_beal

    Difference between stuck high and stuck low

    sudhagar_k

      Hi,

       

           Am using hyperlynx 8.0. As per my understanding,when i assign "stuck low'  to a  victim net in crosstalk analysis,it means that the victim net should be(in ideal case) zero.But due to crosstalk it will pick up some noise. Now what am confused is why would we use "stuck high",i dont understand the point in simulating for the nominal voltage and seeing how much noise it will pick up,definetly the noise should be the same i.e for ex am using a 3.3LVTTL line as victim. In stuck low mode,the ideal voltage should be zero but it picks up "X"mV as noise,while in stuck high mode the ideal voltage should be 3.3V but it should be "3.3+0.X" V.

       

      But in simulation during stuck low mode,am seeing a noise of nearly 240mV. But in stuck high mode,for the same scenario,the maximum voltage is 3.53.

       

      Kindly advise on the difference .

       

      Regards,

       

      Sudhagar

        • 1. Re: Difference between stuck high and stuck low
          yu.yanfeng

          Victim net's driver state is important to do crosstalk analysis because the nature of low impedance for driver will refect crosstalk signal. So you have to check crosstalk on both stuck high and stuck low. Driver's impedance is a little of differant on high state than which on low state, That's why you see different crosstalks on two states.

          Yanfeng

          • 2. Re: Difference between stuck high and stuck low
            sudhagar_k

            Hi Yanfeng,

             

                                In the IBIS model,the pull up is VCC .i.e. 3.3V and the pull down is ground. What i understand is, the driver impedance depends on pullup voltage and pulldown voltage during stuck high and low respectievely. THen how does it vary,am not able to work out the relation between crosstalk,change in driver impedance in different level and  pullup/down voltage level. I guess am confusing a bit.

                                Kindly clarify.

             

            Regards,

             

            Yanfeng

            • 3. Re: Difference between stuck high and stuck low
              yu.yanfeng

              We can calculate driver's impedance based on the V-I curve. For most of drivers, you will find the impdances be little of differance between pullup (stuck high) and pulldown(stuck low). Differance in vitim net's drive impedance make differant crosstalk.

               

              Yanfeng

              • 4. Re: Difference between stuck high and stuck low
                weston_beal

                The driver impedance depends more on the physics of the transistors. This is slightly affected by the pullup or pulldown voltage, but not much. The greater effects are the material doping and geometries. The impedance is a measure of the semiconductor between the pin and the voltage (either Vcc or ground).

                 

                Also, the crostalk is not proportional to the clock frequency. It is more closely related to the rising or falling time of the signal transistions.

                 

                Weston