WEBVTT 00:00.520 --> 00:01.320 Hi everyone. 00:01.400 --> 00:03.040 Welcome to esteemed PCB Academy. 00:03.080 --> 00:04.040 My name is Avril. 00:04.160 --> 00:09.040 In our previous video we talked about LVDS and different terminology we use for LVDS. 00:09.040 --> 00:15.920 For example V differential v common and current mode drivers, along with couple of simulations on cadence 00:15.920 --> 00:16.880 security tools. 00:17.680 --> 00:23.040 We have also discussed different IEEE and Ansi standards for LVDS. 00:23.400 --> 00:25.840 In this video we will focus on simulation part. 00:25.880 --> 00:32.640 We will see how to set up the topology of LVDS driver and receiver along with lossy transmission line 00:32.640 --> 00:34.800 on Security Topology Explorer. 00:35.240 --> 00:39.320 Then we will add Stackup information and Ibis models to make it more realistic. 00:39.560 --> 00:43.920 We will see how to do different measurements on output waveform and diagram. 00:44.200 --> 00:45.440 So let's get started. 00:45.640 --> 00:51.800 So before jumping to the simulation of high speed signals, we should be aware of why we are doing pre 00:51.800 --> 00:52.840 layout simulations. 00:53.440 --> 00:55.640 So let's understand that with an example. 00:55.760 --> 00:59.800 Suppose in our case we need 0.4 GB data rate. 01:00.800 --> 01:06.360 So are these drivers good enough to support that data rate with nice and clean waveform at receiver 01:06.360 --> 01:10.520 side or parasitics and losses will destroy the waveform. 01:11.040 --> 01:15.600 So in short, we do pre layout analysis to define constraints and design rules. 01:16.480 --> 01:20.160 Now let me tell you about few of these constraints we simulate for. 01:21.160 --> 01:22.960 First one is length of a transmission line. 01:23.600 --> 01:28.880 So we simulate length of a transmission line to verify the effect of length or propagation delay on 01:28.880 --> 01:30.560 the signal at receiver side. 01:31.680 --> 01:33.560 Second one is impedance discontinuity. 01:34.200 --> 01:40.280 So on our transmission line there can be impedance discontinuity due to stub and vars on the line. 01:41.120 --> 01:43.320 Third one is stack up and material property. 01:43.680 --> 01:49.640 So we basically analyze what stack up and material property are doing with the waveform by doing pre 01:49.640 --> 01:50.640 layout analysis. 01:52.080 --> 01:57.040 Fourth one is different type of losses like dielectric conductors crosstalk etc.. 01:57.560 --> 02:05.160 So now by running sweep analysis on these parameters We need to find the limit or break even points 02:05.320 --> 02:09.120 for design rules, and we implement these design rules while layout. 02:10.160 --> 02:13.960 Now let's talk about topology and requirement for simulating something. 02:14.800 --> 02:19.560 So in our case we are simulating high speed LVDS drivers and receiver. 02:20.240 --> 02:28.240 And for that I am using TS, DDS, LVDS 1047 driver and DDS LVDS 1048 receiver. 02:29.200 --> 02:33.600 And because these driver and receiver follows Ansi standards. 02:34.080 --> 02:41.120 So drivers differential output and receivers differential inputs should have 100 ohm differential impedance. 02:42.560 --> 02:47.160 Plus we need to terminate it with 100 ohm resistor at the receiver's input. 02:47.640 --> 02:51.680 So as you can see in the figure this is what we are going to simulate. 02:52.360 --> 02:58.840 Now let's move to the simulation requirement part to simulate this topology or to make simulation more 02:58.840 --> 02:59.480 realistic. 02:59.480 --> 03:02.510 Instead of just following the default All simulation. 03:03.110 --> 03:07.270 We need few information from chip manufacturer and PCB manufacturer. 03:07.990 --> 03:12.950 And first one is Ibis model or Spice model, or other circuit models in general. 03:13.190 --> 03:17.190 But in our case we need Spice models only. 03:17.230 --> 03:19.350 Second is PCB stack up information. 03:19.710 --> 03:23.630 So here I mean detailed stack up including materials, property, etc.. 03:25.430 --> 03:32.110 Third one is fixed or variable parameters like data rate, bit pattern, differential impedance, maximum 03:32.110 --> 03:35.310 length supported, maximum number of vars, etc.. 03:36.910 --> 03:39.710 And last but not the least connector models. 03:39.870 --> 03:45.070 So if we are using any connector in our design, we need to include those as well in our simulation 03:45.070 --> 03:48.710 because those also has parasitics in it. 03:48.750 --> 03:54.470 Now with all this information, we are ready for setting up our topology in Security Topology Explorer. 03:55.310 --> 03:59.830 So in the step one we need to open Security Topology Explorer 17.4. 04:00.230 --> 04:02.110 You will get it with couple of licenses. 04:02.470 --> 04:06.150 I'm just going to use security Aurora license and click over. 04:06.190 --> 04:06.550 Okay. 04:07.870 --> 04:08.430 All right. 04:08.670 --> 04:13.990 So now it is asking either you want to open an existing design or want to create a new one. 04:14.350 --> 04:16.270 I'm just going to create new topology. 04:16.790 --> 04:18.830 So here you can set your topology name. 04:19.270 --> 04:28.310 In our case it is LVDS 1047 and 1048 receiver driver topology. 04:29.670 --> 04:31.590 And I'm just going to save it in desktop. 04:34.150 --> 04:39.350 After selecting the folder you have to select either you want to use some template or just go for the 04:39.350 --> 04:40.270 blank topology. 04:40.670 --> 04:42.910 So in our case we're going to create it from scratch. 04:43.070 --> 04:47.030 So we'll just select blank topology and click over create button. 04:48.630 --> 04:55.150 After creating the new topology we have to place driver block from Add block menu. 04:56.350 --> 05:01.870 And if you'll try to place the driver you'll see it is single ended output as of now. 05:02.350 --> 05:06.830 To make it make a differential output, you have to just select differential from here. 05:07.510 --> 05:10.590 And now we are ready to place differential output driver. 05:11.670 --> 05:15.430 Now in the next step we have to add Ibis model in this transmitter. 05:15.590 --> 05:20.270 To do that you have to just double click to open Edit Property tab. 05:20.910 --> 05:23.150 And here you have to select the Ibis file. 05:23.590 --> 05:26.590 Now it will direct you to this load Ibis section. 05:27.110 --> 05:34.950 So as of now you can see we have a default Ibis model assigned to change this to manufacturer's Ibis 05:34.990 --> 05:35.430 model. 05:35.470 --> 05:37.710 You have to just click over this three dot. 05:39.030 --> 05:43.150 And in our case we have saved the Ibis file in desktop. 05:43.350 --> 05:49.310 So I have to just go there and select the Ibis model for driver and open it. 05:49.310 --> 05:53.670 As soon as you select the Ibis model it will direct you to differential pin tab. 05:53.910 --> 05:57.150 And from here you have to select differential pairs. 05:57.150 --> 05:58.550 So it has four channel. 05:58.790 --> 06:03.550 And I am just going to use doubt four plus and doubt four minus channel. 06:05.790 --> 06:10.590 In case you are going to use multiple channels, you can select multiple differential pairs. 06:11.070 --> 06:12.590 I'm just going to uncheck those. 06:13.230 --> 06:19.190 So for this type of topology what you have to do you have to just select the output pins which differential 06:19.190 --> 06:20.990 pins you want to use for output. 06:20.990 --> 06:24.910 So I'm just going to use ten comma nine and click over okay. 06:26.310 --> 06:29.270 And our driver model is ready to use. 06:30.790 --> 06:33.110 Similarly we can setup the receiver model. 06:33.550 --> 06:36.710 So firstly we have to place our differential receiver model here. 06:38.310 --> 06:39.670 Again double click on this one. 06:39.670 --> 06:40.950 Select the Ibis file. 06:42.270 --> 06:48.110 Click on these three dots and select RDS LVDS 1048 Ibis model. 06:48.910 --> 06:49.910 Click on open. 06:50.750 --> 06:57.990 Now for receiver we are going to use pin number two and pin number one as a differential input of receiver. 06:58.870 --> 07:03.550 And we are going to place couple of single data pins which will be enable pins. 07:04.340 --> 07:09.820 Just select those and we're not going to change anything on pin mapping and click on okay. 07:11.220 --> 07:11.700 Alright. 07:11.700 --> 07:13.860 So our receiver model is also ready to use. 07:14.820 --> 07:18.980 So now in both case as of now I am seeing pin numbers on pins. 07:19.300 --> 07:21.020 I just want to change it to net name. 07:21.980 --> 07:25.820 It will be easy to identify which pin is for what purpose. 07:26.620 --> 07:29.620 So I'm just going to slide it down here. 07:31.820 --> 07:37.620 And just arrange positive and negative pins in front of each other. 07:38.580 --> 07:39.100 All right. 07:39.220 --> 07:43.780 And if you zoom in to receiver side we have to enable receiver. 07:44.700 --> 07:45.140 To do that. 07:45.140 --> 07:50.380 You have to just right click over enable pin and connect it to power. 07:51.740 --> 07:55.020 Double click over power and change it to 3.3V. 07:55.500 --> 08:02.420 Similarly, for enable asterisk you have to just connect it to ground and our receiver side is enabled 08:02.420 --> 08:02.660 now. 08:03.900 --> 08:08.340 Alright, so till now we have set up our driver and receiver model. 08:09.420 --> 08:14.540 Now in the next step we have to add trace between transmitter and receiver. 08:15.340 --> 08:21.420 To do that again make sure this differential block is selected and click over trace. 08:24.420 --> 08:26.060 Now to edit the trace property. 08:26.540 --> 08:33.940 As you can see it is 5000 mil longer trace which has 118.673Ω differential impedance. 08:34.540 --> 08:39.340 To edit the trace property, you have to just select it and click over Trace Editor. 08:39.780 --> 08:45.820 Now inside this trace editor, we have to add the stackup that we are going to use in our PCB. 08:46.380 --> 08:50.060 So we'll get this information from our PCB manufacturer. 08:51.340 --> 08:58.940 In my case I'm just going to use this Stackup which is a four layer 1.6mm thick Stackup. 08:59.500 --> 09:01.060 So I'm just going to add it quickly. 09:08.580 --> 09:09.260 All right. 09:09.260 --> 09:13.380 So till here we have added our stack up in this trace editor. 09:14.060 --> 09:18.460 Now in the next step I'm just going to place these tracks on the bottom layer. 09:19.220 --> 09:26.100 To do that you have to just go to that layer name column and double click here and select bottom. 09:28.060 --> 09:30.900 So you can see the traces are shifted to the bottom layer. 09:31.940 --> 09:35.660 Now in the next step again I'm going to change the unit to mill. 09:36.660 --> 09:42.100 So as of now if you see the impedance it is 104.917. 09:42.140 --> 09:47.860 We have to make it more precise to 100 ohm characteristic impedance of differential pair signals. 09:48.180 --> 09:51.380 To do that we have to change the trace width and spacing. 09:52.180 --> 09:57.740 So I have already calculated what should be the trace width and spacing for this stackup from cross 09:57.740 --> 10:00.980 section editor of PCB editor 17.4 tool. 10:01.660 --> 10:03.740 So let's put that value here quickly. 10:05.020 --> 10:09.740 So I have changed the trace width to five mil and spacing to 7.5 mil. 10:10.260 --> 10:15.420 And again, if you're going to calculate the transmission line parameters here you can see the impedance 10:15.420 --> 10:17.460 is very much close to 100 ohm. 10:18.340 --> 10:23.180 Now in the next step you can put the length of the transmission line and change its reference plane 10:23.180 --> 10:23.940 if you want. 10:23.980 --> 10:29.260 So in our case, the reference plane is the nearest plane to bottom layer which is power plane. 10:29.620 --> 10:31.700 So let it be power plane and length. 10:31.700 --> 10:34.220 We are going to simulate for 5000 mil. 10:35.100 --> 10:39.060 Now you can save this trace editor and stack up value. 10:40.020 --> 10:47.220 Just name it stack up for LVDS and save it. 10:48.180 --> 10:53.100 So after setting all this value, you have to just click over this generate element model. 10:53.780 --> 10:56.820 And you can see we have implemented all the changes in trace. 10:57.660 --> 11:04.500 Now after setting all the trace parameters, we have to just connect those to connect driver and trace. 11:04.500 --> 11:12.740 You have to just click over or double click over this driver pin and connect it to a pin of the trace. 11:13.300 --> 11:16.340 And similarly we can connect it to receiver. 11:17.940 --> 11:19.060 Let's do that quickly. 11:22.700 --> 11:22.980 Alright. 11:22.980 --> 11:26.140 Why I'm connecting like this I'll tell you in a few seconds. 11:26.900 --> 11:33.420 So once it is done now in the next step we have to add a termination register at the receiver side. 11:34.100 --> 11:38.820 So to place a register you have to just select Ideal Elements. 11:39.100 --> 11:42.340 Right click and select the register element. 11:43.180 --> 11:43.860 To rotate it. 11:43.860 --> 11:45.700 You have to again right click and click over. 11:46.020 --> 11:51.340 Either you can rotate it left side or right side and place it here. 11:52.940 --> 11:55.740 So as you can see as of now, it is not connected to any pin. 11:56.100 --> 11:58.980 To connect it again you have to follow the same process. 12:02.140 --> 12:05.380 So till now register element is also connected to receiver side. 12:05.980 --> 12:07.970 Now we have to change its value to 100 ohm. 12:08.010 --> 12:12.330 To do that, you have to just select the resistor, go to the Edit Properties section and change it 12:12.330 --> 12:14.650 to 100 and enter. 12:16.770 --> 12:17.290 All right. 12:17.290 --> 12:21.050 So as you can see as of now the topology is ready to simulate. 12:21.610 --> 12:25.050 But before running the simulation we have to add analysis options. 12:26.690 --> 12:32.450 For that you have to just click over set analysis option tab from Workflow or Topology Explorer. 12:33.490 --> 12:35.170 And here you will see three columns. 12:35.810 --> 12:39.170 Data rate number of bits and stimulus pattern. 12:41.010 --> 12:51.530 If you open the data sheet of DDS LVDS 1047, they will find this driver supports up to 0.4 GB data 12:51.530 --> 12:51.930 rate. 12:52.290 --> 12:54.690 So we are going to use the same value here. 12:54.770 --> 12:59.250 As of now and number of bits we can change it to 32 bits. 13:00.450 --> 13:03.210 And for setting the stimulus pattern you have to right click here. 13:03.650 --> 13:05.570 Then left click over define pattern. 13:06.570 --> 13:10.890 Make sure you have selected random from Data Pattern and click over preview. 13:11.730 --> 13:19.410 So these 32 random bits we are going to send over driver differential line and click over okay. 13:20.890 --> 13:28.570 Now in the next step at the receiver side make sure write receiver IO model assigned to write signal 13:28.570 --> 13:36.370 name for example are in one positive should have R in positive receiver model and negative should have 13:36.370 --> 13:37.810 R in minus receiver model. 13:39.330 --> 13:43.330 Now in the next step we need to check the connectivity between transmitter and receiver. 13:44.170 --> 13:51.210 To do that you have to click over check connectivity from Workflow of Topology Explorer and click over 13:51.250 --> 13:51.970 check button. 13:53.290 --> 14:00.810 So as you can see the simulation is ready to use and RX pin two comma one are connected to transmitter 14:00.810 --> 14:03.570 pin or driver pin 910. 14:04.530 --> 14:09.010 Now we can close these menus and we can go for the simulation part. 14:10.170 --> 14:14.410 To simulate this topology, we have to click over Start transient analysis. 14:14.730 --> 14:15.850 Let's click on that. 14:18.810 --> 14:25.610 So as of now we can see three waveforms in this C viewer. 14:26.210 --> 14:27.850 One is for Enable and Enable assist. 14:27.850 --> 14:29.210 We're just going to disable it. 14:29.970 --> 14:34.370 And the other waveform is for R in one plus minus r in one minus. 14:34.890 --> 14:38.890 So this is the output or differential output of received differential signal. 14:39.290 --> 14:44.250 Now to edit the property of this waveform you can just left click over here. 14:44.770 --> 14:48.570 And here you can add the add different styles. 14:48.690 --> 14:52.810 And if you want to add some marker on it you can do that. 14:53.690 --> 14:55.410 And from here you can change the color. 14:55.610 --> 15:02.770 Let's make it red and change the width to two unit and click on okay. 15:03.490 --> 15:05.530 So now this waveform will be like more visible. 15:06.370 --> 15:09.770 Apart from that you can do certain measurements on this one. 15:09.770 --> 15:16.130 Let's suppose I want to measure the rise time and fall time, let's say 10 to 90% of the waveform. 15:16.810 --> 15:23.330 To do that, let's just right click go to measure and click over rise and fall time. 15:25.690 --> 15:26.290 Now here. 15:26.490 --> 15:31.090 So here you will see all the waveform selected from this menu. 15:32.930 --> 15:36.410 And this is the minimum and maximum voltage of this waveform. 15:37.450 --> 15:39.050 And here you can add the percentage. 15:40.290 --> 15:45.090 So when we measure the rise time and fall time for a particular waveform we get two information. 15:45.090 --> 15:49.130 One is what is the rise time or fall time for 10 to 90%. 15:49.650 --> 15:53.050 And what is the rise time and fall time for 20 to 80%. 15:53.290 --> 15:56.490 Now, to do that measurement you have to just click over apply button. 15:57.370 --> 16:02.010 And here you will get the minimum and maximum rise time and fall time for this particular waveform. 16:02.690 --> 16:07.410 Similarly using the markers you can do amplitude measurement. 16:08.370 --> 16:11.240 So we have to just select the vertical voltage measurement. 16:11.440 --> 16:11.840 Okay. 16:13.240 --> 16:15.720 And add these markers at the maximum value. 16:15.840 --> 16:23.440 So from where we'll get peak to peak value of this particular waveform which is 0.671689. 16:24.240 --> 16:27.960 Similarly you can measure the overshoot and undershoot on this waveform. 16:28.520 --> 16:32.360 Now this all the measurement was for receiver output. 16:32.720 --> 16:39.200 Similarly you can do certain measurements for receiver input and driver output. 16:39.960 --> 16:45.040 Because we have added our longer transmission line between driver and receiver. 16:45.960 --> 16:49.920 So we'll see some propagation delay between driver and receiver waveform. 16:50.600 --> 16:52.920 So you can set the marker at a particular voltage. 16:53.280 --> 16:55.920 And from there you will get the delay value. 16:56.080 --> 17:01.480 To do that you have to just select a particular section of the waveform. 17:02.000 --> 17:07.520 Right click go to Measure Difference and this time uncheck vertical. 17:10.200 --> 17:13.440 Now let's set this marker at 1.25V. 17:16.520 --> 17:23.880 And here you can see the clear time difference is 780 5.9 picoseconds. 17:24.160 --> 17:28.160 And you can compare these measurements with the information given on the datasheet. 17:29.400 --> 17:33.400 So this is one kind of waveform measurements. 17:33.840 --> 17:38.800 Or from these measurements we can maintain the signal integrity of the waveform. 17:39.520 --> 17:42.560 There is one more way to measure the signal integrity of the waveform. 17:43.080 --> 17:44.400 And that is eye diagram. 17:44.920 --> 17:49.520 We are going to learn more about eye diagram and jitter in the next video. 17:50.320 --> 17:52.360 So I will add this project in the description. 17:52.360 --> 17:53.440 You can download it. 17:54.800 --> 18:00.320 And to run this simulation you need the free trial of Sigrity Aurora and other security tools. 18:00.760 --> 18:02.560 I have added a link in the description. 18:02.560 --> 18:05.720 You can go there and register for getting the free trial. 18:06.640 --> 18:08.520 And there you can run these simulations. 18:09.040 --> 18:10.400 So see you in the next video.