WEBVTT 00:01.120 --> 00:03.600 Hi everyone, welcome to SDM, PCB Academy. 00:03.600 --> 00:04.520 My name is Amirul. 00:04.720 --> 00:08.560 In this video we are going to talk about what is high speed AI diagram. 00:08.960 --> 00:13.880 We will see what is the purpose of using it and how to do different measurements on AI diagram. 00:13.880 --> 00:18.880 For example jitter I height, width or the amount of distortion etc.. 00:19.600 --> 00:24.760 We will also discuss what is eye mask along with couple of simulations on cadence Sigrity topology explorer 00:24.760 --> 00:25.880 17.4. 00:26.080 --> 00:27.320 So let's get started. 00:31.240 --> 00:33.440 We will start with very first question. 00:33.800 --> 00:35.920 What is an eye diagram or eye pattern? 00:36.600 --> 00:41.360 An eye diagram is used to get a good idea of signal quality in digital domain. 00:41.360 --> 00:48.840 In other words, we can say eye diagram is superposition of all the data bits on an z or z channel. 00:49.720 --> 00:56.280 Using eye diagram we can do following measurements like amount of distortion, time variation at zero, 00:56.280 --> 00:59.570 crossing Best or worst signal to noise ratio. 01:00.170 --> 01:03.290 Sensitivity of timing using I slopes, etc.. 01:03.530 --> 01:06.530 We'll understand these in more detail later in this video. 01:06.690 --> 01:11.890 But first let's talk about the formation of an eye pattern from data Bits. 01:17.050 --> 01:23.050 Now, before plotting an eye diagram, I just want to explain a few terminologies or basic terms we 01:23.050 --> 01:23.490 use. 01:23.610 --> 01:25.490 Let's say this is a crow screen. 01:25.970 --> 01:29.650 And here on the vertical axis we have amplitude or voltage. 01:29.970 --> 01:32.770 And on the horizontal axis we have time. 01:33.410 --> 01:40.450 And the area where we plot eye diagram we represent it with TB or symbol duration. 01:40.450 --> 01:45.370 We also call it a unit interval or we represent it with one UI. 01:45.850 --> 01:48.250 So I diagram should be within this area. 01:48.970 --> 01:54.890 Now let's say I'm sending following serial bits on a channel which is a polar Non-return to zero channel 01:55.650 --> 01:56.330 for that. 01:56.490 --> 01:59.650 Let's say the voltage scale is plus minus x volt. 02:00.090 --> 02:07.330 Then one bit means we send or receive x volt, and zero means we'll send or receive minus x volt. 02:08.530 --> 02:09.090 All right. 02:09.210 --> 02:14.330 So till here we have drawn a polar energy channel for a particular serial data base. 02:14.810 --> 02:20.730 Now let's plot an eye diagram for a crow for one time duration or one symbol duration. 02:20.850 --> 02:27.650 We represent it with one TB, which will be nothing, just the overlap of all the data bits from polar 02:27.650 --> 02:28.530 energy channel. 02:28.810 --> 02:29.730 So let's do that. 02:29.730 --> 02:35.530 For one it will go to plus x volt, and for zero it will go to minus x volt and all the symbols will 02:35.530 --> 02:36.490 be overlapped. 02:37.490 --> 02:38.210 So that's it. 02:38.210 --> 02:43.410 This is the eye diagram or eye pattern that we have created from energy channel. 02:43.850 --> 02:45.610 And here it is fully open. 02:46.010 --> 02:50.370 Or you can say an ideal eye because there is zero distortion. 02:50.700 --> 02:52.620 or you can say no AC problems. 02:53.380 --> 03:00.100 Similarly, we can create an AI diagram using polar channel in polar return to zero channel. 03:00.260 --> 03:05.620 We represent one with plus x volt and zero with minus x volt. 03:05.620 --> 03:11.860 But the difference is signal should start from zero and return to zero within one sample duration or 03:11.860 --> 03:12.620 one TB. 03:12.660 --> 03:19.420 As you can see in your screen for creating an AI pattern using AWS representation, the process is similar 03:19.420 --> 03:20.300 to NS. 03:20.500 --> 03:23.740 We have to overlap bits from AWS channel. 03:24.260 --> 03:29.260 For example, one will go like this and zero will go to minus x volt and return to zero. 03:30.740 --> 03:36.820 So this is also an ideal AI diagram because of no distortion or no AC problems. 03:37.540 --> 03:42.820 Now I am going to give you one example of non-ideal AI diagram using polar channel. 03:43.300 --> 03:49.540 So as you can see on the screen we have ISI problem on the channel which is represented with highlighted 03:49.540 --> 03:50.020 part. 03:50.540 --> 03:57.300 Now in this case, if I will overlap bits, it will either start before the symbol duration or finish 03:57.300 --> 03:58.540 after symbol duration. 03:58.980 --> 04:02.980 And in result we can see clearly the distortion on the eye pattern. 04:03.540 --> 04:05.700 So this was ISI problem on the channel. 04:06.660 --> 04:07.220 All right. 04:07.220 --> 04:12.300 In the next step I am going to demonstrate a good and bad eye pattern on Security Topology Explorer. 04:12.300 --> 04:14.620 And then we will talk about measurements in detail. 04:19.740 --> 04:22.660 For that let's open Topology Explorer 17.4. 04:23.660 --> 04:25.140 This is LVDS topology. 04:25.260 --> 04:28.860 And I am following all the design guidelines for the signaling scheme. 04:29.420 --> 04:35.780 So let's run the transient analysis and expected eye pattern should be clear with minimum distortion. 04:36.140 --> 04:39.340 So let's click here to check the eye pattern. 04:39.340 --> 04:42.660 And as you can see the distortion is very minimum here. 04:42.700 --> 04:46.670 On the other hand I am I am going to simulate a topology with impedance discontinuity. 04:46.870 --> 04:48.230 So let's do that as well. 04:48.950 --> 04:53.270 As you can see here in this topology we have impedance discontinuity on the transmission line. 04:53.910 --> 04:55.870 And we have added a VI as well. 04:56.070 --> 04:58.470 So let's run the transit analysis and see the results. 04:59.830 --> 05:02.030 So as you can see the waveform is also not good. 05:02.230 --> 05:03.670 Let's plot for eye diagram. 05:04.230 --> 05:07.990 And as expected the eye is collapsed due to impedance discontinuity. 05:09.430 --> 05:14.630 Now in the next step I am just going to talk about all the measurements that we can do on eye diagrams. 05:19.710 --> 05:24.150 In this section I'm going to talk about different measurements we can perform on eye diagram. 05:24.550 --> 05:26.430 First one is amount of distortion. 05:26.630 --> 05:32.710 So distortion on eye diagram is due to ISI or due to noise appears as closure of eye patterns. 05:33.070 --> 05:36.710 So it should be less on eye diagram as you can see on your screen. 05:37.470 --> 05:42.600 Another measurement that we can perform on eye I diagram is time variation at zero crossing. 05:42.640 --> 05:49.120 We also call it timing jitter which measures the time deviation from ideal timing of a data base. 05:49.480 --> 05:51.120 So we represent it with delta t. 05:51.160 --> 05:57.640 As you can see on the diagram for calculating the timing jitter peak to peak percentage we use a formula 05:57.680 --> 05:59.600 delta t divided by TB. 05:59.800 --> 06:04.040 So here TB is symbol duration multiplied by 100. 06:04.080 --> 06:07.120 Third one is signal to noise ratio at sampling point. 06:07.120 --> 06:13.080 So it is nothing but the ratio of desired signal level 0 to 1 divided by levels of background noise, 06:13.120 --> 06:14.640 plus any distortion on it. 06:15.400 --> 06:20.200 So either you can use this formula to calculate the signal to noise ratio at sampling point, or you 06:20.200 --> 06:23.280 can directly measure it on I diagram as shown in the figure. 06:24.640 --> 06:29.200 Fourth, measurement that we can perform on I diagram is sensitivity in timing errors. 06:29.560 --> 06:33.560 It is the rate at which eye closes and the sampling time varies. 06:34.560 --> 06:38.520 Using this rate we got to know the know the possibility of timing errors on the channel. 06:39.120 --> 06:42.120 Measurements of sensitivity in timing errors is very simple. 06:42.240 --> 06:43.640 We need to measure this slope. 06:43.720 --> 06:45.200 As you can see in the figure. 06:45.320 --> 06:49.920 To estimate timing errors and error increase as slope becomes more flat. 06:50.960 --> 06:52.280 Next is mean of signal. 06:52.400 --> 06:55.400 It is half of ideal signal or peak to peak amplitude. 06:55.440 --> 06:57.280 As you can see in the eye diagram. 06:58.440 --> 07:01.840 Another measurement that we can perform on eye diagram is eye width. 07:01.960 --> 07:07.640 So if width is very important measurement, it tells us the time over which signal can be successfully 07:07.680 --> 07:08.320 sampled. 07:09.600 --> 07:15.120 From this measurement we can verify the measure time with minimum sampling time given on the data sheet 07:15.160 --> 07:16.040 of receiver. 07:17.400 --> 07:23.200 Last but not the least is amplitude jitter or amplitude noise, which is the noise at one crossing. 07:23.240 --> 07:24.960 As you can see in the eye diagram. 07:26.720 --> 07:28.080 So that's it for this video. 07:28.160 --> 07:34.000 In the next video I will talk about eye mask and how to create and apply an eye mask using data sheet.