Well, lets think about this buffer for a moment. From your file it calls this buffer: [Model type] I/O_open_sink An open sink buffer does not have a pullup device. The drain (collector) node of the pulldown device is not connected to a pullup device. So, there is no source of current pulling the load up to Vdd. So, if you have a resistance tied to ground such as the 500 Ohm resistor in your example and the pulldown device is on you will have both sides of the resistor at ground potential. If the pulldown device is off then the ground side of the resistor is grounded and the end tied to the buffer is now floating. There is nothing to pull that node to any other voltage other than ground. Conversely, if your 500 Ohm load is tied to Vdd then the pulldown device can make one end of the resistor approach ground potential while the end of the resistor tied to Vdd will remain at Vdd. So, you should see transitions when the load is tied to Vdd but you cannot see any transitions when the load is tied to ground. For the grounded load to have a transition you need to have a path from the power supply through the load to ground and back through the power supply. In electronics there must be a complete circuit of some kind for current to flow. Since the impedance between the supply to the load resistor is high (read open circuit) there is no where for the electrons to flow. Conversely one could compute the current as I = E/R. In your case E = 3.00 Volts in the typical case but the R is an open circuit - R is close to infinity. Thus the current is close to zero. Thus from Ohms Law again (E = IR) 0.0000000000000A * 500 Ohms = 0.000 Volts. 99.9999% of the open sink buffers I have seen do not have a powerclamp or a pullup thus there is no need for the powerclamp or pullup references. Since there is no pullup you do not need to have these two lines: [Rising waveform] 500 0 0 0 NA NA NA NA NA [Falling waveform] 500 0 0 0 NA NA NA NA NA For the ramp section IBIS will take the dV/dT_r from the load to ground and will take the dV/dT_f from the load to Vdd in a push pull buffer. Since you told the conversion program there was rising falling waveforms with the load terminated to ground the program is taking the data that cannot be. If these two lines are not present then for this buffer the dV/dT_r and dV/dT_f will be taken from the rising terminated to Vdd and falling terminated to Vdd. Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@teraspeed.com www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 -----Original Message----- From: lau yy [mailto:tok47@hotmail.com] Sent: Monday, October 17, 2005 5:02 PM To: tom@teraspeed.com; ibis-users@eda.org Subject: regarding the rising n falling waveform again Dear Tom, Is me agian, the guy who asking the rising/falling waveform. This time, I facing another problem, and wish to have your opinion. The recent model that I build, where having pullup problem. The problem is no mather how I change the IN and EN of my IO pins, I cant get the dv/dt_r in positive value although I set my model as I/O_OPEN_SINK. For the falling waveform, although is look fine but also fail for the checker for 0v references. The rising waveform is not working for 0v references and vcc references. The data is state at some value, it do change in a small scale but not showing a rising. Is my model got problem or the circuit itself got problem? or there were other problems? Below were my setting : [Model] IO0 [Model type] I/O_open_sink [Power clamp reference] 3.00 2.70 3.60 [Gnd clamp reference] 0 0 0 [Pullup reference] 3.00 2.70 3.60 [Pulldown reference] 0 0 0 [Rising waveform] 500 0 0 0 NA NA NA NA NA [Rising waveform] 500 3.00 2.70 3.60 NA NA NA NA NA [Falling waveform] 500 0 0 0 NA NA NA NA NA [Falling waveform] 500 3.00 2.70 3.60 NA NA NA NA NA [Vinl] 0.8 [Vinh] 2.10 [Cref] 30pF [Vmeas] 1.50 [Rload] 50 [Model file] hsp.mod hspmin.mod hspmax.mod Here, my ramp data : [Ramp] | variable typ min max dV/dt_r -0.6000m/-0.2000n -1.2000m/0.4000n -0.6000m/-0.2000n dV/dt_f 0.7236/2.6060n 0.4002/4.0761n 1.3476/1.4710n ANd here the error message of my Falling waveform : ERROR - Model IO0: The [Falling Waveform] with [R_fixture]=500 Ohms and [V_fixture_max]=0V has MAX column DC endpoints of 0.00V and 3.40v, but an equivalent load applied to the model's I-V tables yields different voltages ( 0.00V and 0.00V), a difference of 100.00% and 178015.78%, respectively. Thanks rdgs yylau |------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993Received on Mon Oct 17 17:37:26 2005
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