WEBVTT 00:00.520 --> 00:01.200 Hello everyone! 00:01.200 --> 00:02.960 Welcome to Typekit YouTube channel. 00:03.000 --> 00:09.080 My name is Amirul and in a previous video I talked about what is impedance and how to bridge real and 00:09.080 --> 00:12.800 ideal world to get better results on modeling and simulation. 00:13.160 --> 00:18.680 And we have also discussed why we don't want any impedance discontinuity on our transmission line. 00:18.920 --> 00:24.680 Now further on this today we will talk about what is single ended impedance and how to estimate impedance 00:24.680 --> 00:29.200 profile for one or more than one tracks using cadence cross section editor. 00:29.400 --> 00:30.640 So let's get started. 00:31.320 --> 00:33.520 We will start with very first question. 00:33.520 --> 00:35.320 What is single ended impedance? 00:35.760 --> 00:41.760 Single ended impedance is same as instantaneous and characteristic impedance of a single ended signal, 00:42.800 --> 00:46.840 and single ended signals are signals which are not coupled with any adjacent signal. 00:49.160 --> 00:54.200 Now in the next topic, let's talk about types of single ended signals and their impedances. 00:54.560 --> 01:00.600 First one is microstrip single ended signal, which has signal on the top layer and return plane on 01:00.600 --> 01:06.680 the bottom layer to estimate the characteristic impedance of this type of signal, you can use this 01:06.680 --> 01:09.760 equation or you can use cross section editor to estimate it. 01:09.840 --> 01:12.560 I'll show you later in this video. 01:12.600 --> 01:16.120 Second one is Stripline single ended signals on a strip line. 01:16.120 --> 01:20.920 We have signals sandwiched between two return plane and to estimate the characteristic impedance, you 01:20.920 --> 01:24.560 can use this equation or you can simply use cross section editor. 01:25.480 --> 01:29.040 Apart from these two, there are two more types of single ended signals. 01:29.720 --> 01:33.720 One is embedded microstrip and another one is asymmetric stripline. 01:33.720 --> 01:35.280 For that you can refer this image. 01:35.280 --> 01:39.720 And here they have given their formulas for calculating characteristic impedance. 01:40.960 --> 01:46.360 Let's move to demonstration part of single ended impedance using cadence PCB editor and cross section 01:46.360 --> 01:49.320 editor for that open PCB editor 17.4. 01:50.200 --> 01:53.400 And this is the board file on which we are going to route a couple of tracks. 01:53.680 --> 01:59.800 So as you can see all these unrouted tracks are 50 ohm impedance track here and here. 01:59.920 --> 02:02.160 So we have four tracks that we need to route. 02:02.480 --> 02:08.920 Let's start with width calculation for these 50 ohm tracks for that open cross section editor. 02:12.040 --> 02:13.680 And click over Primary View. 02:15.160 --> 02:23.440 Now if you go to the left side here you will find an tab or column which is signal integrity. 02:23.680 --> 02:24.760 Just click over here. 02:25.200 --> 02:25.800 All right. 02:27.040 --> 02:32.880 And here you will find we have added a impedance value. 02:33.080 --> 02:36.160 Based on that we are getting width for example. 02:36.240 --> 02:40.440 So as you can see here as of now we have added 50 ohm impedance. 02:40.560 --> 02:43.440 If I change it to 100 ohm the width will vary. 02:43.640 --> 02:51.280 So using this calculator we can able to calculate what should be the width of track in a mill for a 02:51.280 --> 02:52.960 particular target impedance. 02:53.200 --> 02:55.760 So in our case we are going to route a 50 ohm track. 02:55.760 --> 03:02.600 So that's why I have noted down these three values for all the 50 ohm impedances on different layers. 03:03.760 --> 03:08.040 Now as you can see for the top layer the value is manufacturable. 03:08.120 --> 03:15.120 The width is manufacturable, but for layer two and bottom layer it is little bit at the high end side, 03:15.120 --> 03:17.800 which is 110 and 124mm. 03:18.160 --> 03:18.760 All right. 03:19.000 --> 03:23.240 So that means this width is too high for routing a track. 03:23.480 --> 03:27.720 So that is how we got to know on which layer we are going to route for a particular stackup. 03:27.920 --> 03:31.120 So we are going to route our 50 ohm track on top layer. 03:31.760 --> 03:34.440 Now we'll click over apply and okay. 03:35.640 --> 03:41.280 Now in the next step we'll going to define constraint set for these four nets. 03:41.560 --> 03:42.040 All right. 03:42.080 --> 03:44.040 To do that open constraint manager. 03:45.840 --> 03:49.520 And here you have to go to physical and all layers. 03:50.480 --> 03:52.720 And under this we have to define the constraint. 03:52.760 --> 03:55.280 To do that you have to right click over DSN. 03:56.280 --> 03:59.080 Go to create and create physical Cset. 04:00.160 --> 04:02.120 You can name it 50 ohm. 04:03.680 --> 04:04.480 And okay. 04:04.960 --> 04:10.920 So after creating constraint set of 50 ohm Under that, we'll get all the layer information that we 04:10.960 --> 04:13.000 have defined during layer Stackup. 04:13.280 --> 04:19.840 But in our case, we have to put all the information for top layer L1 and bottom layer for linewidth 04:19.840 --> 04:23.320 that we have calculated during the impedance calculation. 04:23.400 --> 04:25.040 So I'm just going to put that quickly. 04:29.000 --> 04:35.520 So once you have added all the details for top layer L1 and bottom layer we'll just close it and click 04:35.520 --> 04:37.760 over knit all layers. 04:37.960 --> 04:45.800 Now here we have to find all the four nets that we we are going to route and change its constraint set 04:45.840 --> 04:47.720 from default to 50 ohm. 04:48.600 --> 04:49.760 So there are four nets. 04:49.840 --> 04:53.520 One is P4 and p5. 04:54.480 --> 04:55.520 So these are the two. 04:55.960 --> 04:58.720 And here if you select you will get 50 ohm option. 04:58.720 --> 04:59.920 You have to just select it. 05:00.280 --> 05:06.720 So once you select 50 ohm you will get all the three layer track widths are already defined here. 05:06.720 --> 05:09.760 And same will do for P5. 05:09.760 --> 05:09.800 Five. 05:10.840 --> 05:13.040 Another two nets are net. 05:13.920 --> 05:14.800 R 34. 05:14.920 --> 05:15.760 Underscore two. 05:17.120 --> 05:19.080 So it should be somewhere here. 05:19.400 --> 05:23.720 This is the one and one is R 36. 05:23.760 --> 05:24.720 Underscore two. 05:25.840 --> 05:26.440 All right. 05:26.440 --> 05:32.360 So here we have assigned the correct constraint set to all these nets. 05:32.680 --> 05:33.920 Now let's close it. 05:33.920 --> 05:36.920 And we are okay to route to route it. 05:36.920 --> 05:40.480 First you have to just zoom in a little bit. 05:40.520 --> 05:46.360 Just click over all on select the pad and press F3 on your keyboard. 05:46.480 --> 05:52.200 So it will automatically pick the correct width that we have defined on Constraint Manager. 06:01.880 --> 06:05.720 So this is how we can route a 50 ohm controlled impedance tracks. 06:06.640 --> 06:08.600 I'll put that project link in the description. 06:08.600 --> 06:12.720 You can download it from there and practice whatever we have learned in this video.