 Hello everyone, my name is Ms. Shweta Yaspatil, working as an assistant professor in electronics and telecommunication engineering department at Walshchand Institute of Technology, Solar Pool. Today's topic for the discussion is the parameters of digital IC. Learning Outcomes At the end of the session, the learners will be able to explain the characteristic of a detailed logic family with typical values. Let us begin and explain the terms associated with the TTL gate. Contents First is the semiconductor digital ICs, advantages of digital ICs, third is the classification of digital ICs, fourth is the characteristic or parameters of digital ICs. Semiconductor Digital ICs The digital systems like digital measuring instruments, computers or microprocessor chips require hundreds of logic gates in the form of switches. If the mechanical switches are used in such systems, then the operation will be quite complex, which requires more power and big circuit because mechanical switches are tangible switches which require some manual work and big circuit because there is a driver required for the mechanical switches. These difficulties are reduced by using semiconductor technology such as diodes, transistors and MOSFETs. All these are used as electronic switches instead of mechanical switches. These semiconductor devices are much faster and they are manufactured on single chip or in a single package. Advantages of ICs First high speed, second is the small size, third is the lightweight of the IC, fourth is the low power consumption and more reliable. Because of these all advantages, digital ICs are used. Specification of digital ICs In unipolar logic family, there is a p-channel MOSFET, n-channel MOSFET and complementary MOSFET. In non-saturated bipolar logic family, there is a Scotky TTL emitter coupled logic. In saturated bipolar logic family, there is a resistor transistor logic, diode transistor logic and transistor transistor logic, parameters of the digital ICs. The performance and the quality of integrated chip or IC depend on their characteristics. Similarly, the popularity and the cost of semiconductor family depends on various characteristics. The manufacturer specifies these characteristics in the manual or data sheet so that user can select that chip for a particular application. There are total seven characteristics. Propagation delay that is speed of operation, power dissipation, figure of merit, fan in and fan out, voltage parameters, noise immunity or noise margin, operating temperature. Cost propagation delay This is the input waveform given with respect to time and at the output we get this waveform with respect to time. The propagation delay is defined as the time required to change the output from one logic state to other logic state after input is applied and it is denoted by T to the base P. TP HL, delay required to change from high to low state is nothing but the TP HL and it is known as turn off delay because at the output from high state to low state output is changed we get zero output. TP LH, delay required to change from low to high state is known as TP LH that is turn on delay. At the output we get the high signal for example for TTL logic family TP is equal to 10 nanosecond. It takes 10 nanosecond time to change the output from one state to other state. Higher is the propagation delay, lower is the speed. Rise time and fall time do not have to be the same. Power dissipation is the second characteristic. The characteristic which is indirectly related with the propagation delay is power dissipation of logic family. The low power dissipation is desirable because it generates less heat and therefore it avoids cooling, power supply and cost problem. Low power dissipation means it should operate with the minimum voltage and the minimum current. Example, a gate takes 2 milliampere current and it is operated with 5 volt supply then its power dissipation per gate is calculated as 2 milliampere into 5 volt is equal to 10 milliwatt figure of merit. It is defined as the product of propagation delay and power dissipation of the gate. Mathematically we can write like this. For the example FM is equal to 10 nanosecond into 10 milliwatt we get 100 tico joule. The lowest figure of merit indicates the best performance. Both these characteristics that is propagation delay and power dissipation are expressed in terms of figure of merit. The required current can be adjusted by increasing the resistance but it increases the time because t is equal to r into c. If resistance of the circuit is increased to reduce the current or power dissipation then propagation delay this t increases. In opposite way if propagation delay this t is reduced to make it faster by reducing the resistance then more current is drawn by the gate which increases the power dissipation. Fan-in and fan-out. Fan-in is the number of inputs to a gate. The capacity of driving the load of a gate is expressed in terms of fan-out. Why fan-out is defined as the number of gates from the same family which are driven reliably. Fan-out is also known as loading factor. Example of that in case of TTL fan-in and fan-out is 10. That is maximum 10 TTL gates can be connected to output terminal of a TTL gate. Voltage parameter. This is the input profile and voltage parameters are shown in this diagram. From 2V to 5V is VIH. IH means high level input voltage and VIH minimum. It is the minimum input voltage which is recognized by the gate as logic 1 or high. VIH is the low level input voltage. And VIH max it is the maximum input voltage which is recognized by the gate as logic 0 or low. This is the output profile for the IC or chip. Here VIH is nothing but the high level output voltage. VIH minimum is the output voltage which is recognized by the gate as logic 1. VIH is from 2.4V to 5V. VIH minimum is always 2.4V. Because of 2.4V IC can recognize the logic 1. The range for the VIH is from 0V to 0.4V. That is low level output voltage. VIH max it is the maximum output voltage which is recognized by the gate as logic 0. And it is always 0.4V. Noise immunity. Here 2 gates are shown as N1 and N2. This N1 is called as driver gate and this N2 is called as load gate. Here for this output is considered VOL max is equal to 0.4V. And for this gate N2 gate VIL max is considered that is 0.8V. Because of this noise voltage is generated that is 0.4V maximum. Noise margin is defined as the maximum noise voltage a device can withstand without making a false change in output. VOL max is equal to 0.4V driver output and VIL max is equal to 0.8V load input. The difference between these 2 is known as noise immunity. Noise immunity can be written as VIL max minus VOL max VOH minimum minus VIH minimum. Operating temperature. In commercial application IC plastic package with temperature range of 0 degree Celsius to 70 degree Celsius is used. Although some sub families have an extended range of minus 40 degree Celsius to plus 125 degree Celsius. These are the references. Thank you.