WEBVTT 00:00.400 --> 00:05.640 In our previous lectures, you learned about Boolean algebra expressions and how to implement them using 00:05.640 --> 00:06.480 logic gates. 00:07.000 --> 00:11.000 And in this lecture, you will learn how to implement logic gates directly in a hardware. 00:11.760 --> 00:14.440 Now transistor we will start with transistors here. 00:15.080 --> 00:20.880 These are solid state electronic devices that act as tiny electronic switches controlling the flow of 00:20.880 --> 00:22.280 electrical signals. 00:22.320 --> 00:29.920 Now, we have already discussed the idea of on off switches here in our previous lectures conceptually. 00:30.320 --> 00:33.880 And now we will explore how these switches are physically built. 00:34.160 --> 00:40.600 Now, to help you fully understand how transistors operate, we will start with a simple and clear introduction 00:40.600 --> 00:41.920 to basic electronics. 00:42.640 --> 00:50.120 And after that you will see how transistors can be connected together in pairs or groups to make faster, 00:50.120 --> 00:53.520 more efficient switches that use less electrical power. 00:53.800 --> 00:59.640 And finally, we will discuss some practical tips and considerations when using transistors to build 00:59.640 --> 01:01.520 actual logic gates. 01:01.560 --> 01:06.630 Now you don't need to be an electrical engineer to understand how logic gates are built at the hardware 01:06.630 --> 01:07.270 level. 01:07.350 --> 01:13.910 However, having a basic understanding of how few simple electronic concepts will make learning much 01:13.910 --> 01:14.550 easier. 01:14.590 --> 01:20.070 Now, in this lecture, we will provide you with a quick and friendly overview of the key concepts you 01:20.070 --> 01:20.750 need to know. 01:21.390 --> 01:25.110 And let's begin with the two fundamental definitions. 01:25.670 --> 01:28.270 What is current now? 01:28.790 --> 01:32.070 Current refers to the movement of electrical charge. 01:32.750 --> 01:39.830 Electrical charge is measured in units called coulombs, written as Si. 01:40.630 --> 01:50.510 Now, if a flow of one coulomb of charge passes a point in one second, which is one coulombs second, 01:50.790 --> 02:02.310 that flow is defined as one amp, ampere or uppercase A, often simply called as amp. 02:03.030 --> 02:06.210 Now current can flow through an Electrical circuit. 02:06.250 --> 02:17.890 If there is a completely connected path from one side of the battery or some power source to the other, 02:18.690 --> 02:24.930 if the circuit is broken at any point, no current can flow. 02:25.730 --> 02:26.450 Voltage. 02:27.010 --> 02:27.730 Voltage. 02:28.010 --> 02:35.730 Also called potential difference, which refers to the difference in electrical energy per unit charge 02:35.730 --> 02:38.490 between two points in an electrical circuit. 02:39.090 --> 02:46.930 Now, one volt is defined as the potential difference between two points. 02:47.170 --> 02:58.610 When a current of one ampere flowing through a conductor results in the dissipation of one watt of power. 02:59.130 --> 03:06.730 In simple words, voltage is like the pressure pushing the electrical current through the circuit. 03:07.560 --> 03:14.840 A computer at its lowest level, it's made from a combination of different electronic components. 03:15.280 --> 03:20.040 Here are the main types the power sources. 03:20.800 --> 03:25.280 These provide the electrical power needed to run the circuits. 03:26.000 --> 03:27.400 Passive components. 03:28.120 --> 03:35.080 These affect current flow and voltage levels, but cannot be controlled or changed by other electronic 03:35.080 --> 03:35.920 components. 03:36.400 --> 03:39.560 Examples include resistors and capacitors. 03:40.360 --> 03:42.600 Active components. 03:43.320 --> 03:50.120 These are components that can switch between different states like on, off, or other configurations 03:50.600 --> 03:53.320 under the control of other electronic signals. 03:53.840 --> 03:57.920 Transistors are the most important active components. 03:58.600 --> 03:59.440 Conductors. 04:00.200 --> 04:06.120 These are materials, usually wires, that connect all the components together and allow electrical 04:06.120 --> 04:07.320 signals to flow. 04:08.080 --> 04:14.300 Next, we will dive deeper into how each of these components behaves and how they are used to create 04:14.340 --> 04:17.740 real working logic gates inside your computer. 04:18.460 --> 04:25.860 In almost all countries, electrical power comes in the form of alternating current a c. 04:26.060 --> 04:34.220 Now for AC, a plot of the magnitude of the voltage versus time shows a sinusoidal wave shape. 04:34.860 --> 04:43.780 Now, computer circuits use direct current DC power, which, unlike AC, does not vary over time. 04:44.060 --> 04:49.260 As you can see here, the AC has sinusoidal, but the DC has just a long line. 04:49.980 --> 04:59.820 Now, if a power supply is used to convert AC to DC as shown in this diagram here. 05:00.580 --> 05:08.020 Now batteries also provide DC electrical power when drawing circuits. 05:08.140 --> 05:12.690 We use the symbol for a battery to designate a DC power supply. 05:13.010 --> 05:20.090 The power supply in the example provides five volt DC five v DC. 05:20.770 --> 05:27.730 And here you can see here it's a circuit symbol for five volt DC. 05:28.570 --> 05:33.050 Now in our previous lectures you have seen that everything that happens inside the computer is based 05:33.050 --> 05:36.690 on a system of ones and zeros. 05:37.130 --> 05:44.490 But you may ask here how are these ones and zeros physically represented? 05:44.850 --> 05:52.730 Now computer circuits distinguish between two different voltage levels to represent logical zeros and 05:52.730 --> 05:54.130 logical ones. 05:54.970 --> 06:09.890 Now logical zero for example may be represented as zero volt DC as this means logical 0 or 5 v DC as 06:09.930 --> 06:21.030 a logical 1 or 0 v The sea as logical 0 or 3.3 V, which is common in computers. 06:21.870 --> 06:24.870 One logical one here. 06:25.630 --> 06:36.150 Now the reverse could also be implemented like the five v DC as logical 0 or 0 v, this as logical one. 06:36.710 --> 06:42.990 Now the only requirement is that the hardware design remains consistent throughout. 06:43.350 --> 06:47.310 Now luckily programmers don't need to worry about the actual voltages used. 06:47.350 --> 06:53.830 This is handled by the computer hardware engineers, which in future I hope it will be you. 06:54.670 --> 07:01.430 Also, keep in mind that electronic devices are designed to operate reliably within a certain range 07:01.430 --> 07:02.230 of voltages. 07:02.270 --> 07:11.870 Now, for example, a device, for example, meant to a device meant to operate at a nominal five volts 07:12.630 --> 07:25.980 typically has a tolerance of plus or 5%, which meaning it can safely operate between 4.75V. 07:26.740 --> 07:32.860 True, maximum volt is going to be 5.25V. 07:33.340 --> 07:38.980 Now, the components inside the computer circuit are constantly switching between these two voltage 07:39.180 --> 07:39.900 levels. 07:40.300 --> 07:47.780 Now each switch takes a tiny amount of time, and this time limits how fast a circuit can complete operations. 07:48.180 --> 07:55.140 As you will see later in the transistors lectures now, trying to switch faster requires more electrical 07:55.140 --> 07:57.100 power, which creates heat. 07:57.900 --> 08:03.700 Now, excessive heat can damage the components and limits the overall speed and calculations, and the 08:03.700 --> 08:07.100 time dependent behavior of electronic components is critical. 08:07.100 --> 08:10.380 Design concentration for hardware engineers. 08:10.900 --> 08:16.380 Now next, we will dive deeper into how each of these components behaves and how they are used to create 08:16.380 --> 08:19.140 real working logic gates inside your computer.