INTEGRATED CIRCUIT LOGIC FAMILY ©2009, CE Department

Introduction ICs have made digital systems more reliable by reducing the number of external interconnection from one device to another. ICs have reduced the amount of electrical power needed to perform a given function. IC cannot handle very large currents or voltages because the heat generated in such small spaces would cause temperature to rise beyond acceptable limits ICs are principally used to perform low-power circuit operations that are commonly called information processing. ©2009, CE Department

Introduction Rapidly growth from SSI, with fewer than 12 gates per chip; through MSI, with 12 to 99 equivalent gates per chip Others – LSI, VLSI, ULSI and GSI There are some things IC cannot do – when deal with very large current ©2009, CE Department

Digital IC Terminology VIH (min) – High level input voltage. The minimum level required for a logical 1 at an input. Any voltage below this level will not be accepted as a HIGH by the logic circuit VIL (max) – The maximum input voltage for logic zero VOH (min) – The minimum voltage level at a logic circuit output in the logic 1 state under defined load conditions ©2009, CE Department

Digital IC Terminology (cont.) VOL (max) – Low level output voltage. The maximum voltage level at a logic circuit output in the logical 0 state under defined load conditions IIH – High level input current. The current that flows into an input when a specified high level voltage is applied to that input IIL – Low level input current. The current that flows into an input when a specified low level voltage is applied to that input ©2009, CE Department

Digital IC Terminology (cont.) IOH – High level output current IOL – Low level output current ©2009, CE Department

Exercise Describe the input and output logic for IC 7442 ©2009, CE Department

Fan out Also known as loading factor Defined as the maximum number of logic inputs that an output can drive reliably A logic circuit that specify to have 10 fan out can drive 10 logic inputs ©2009, CE Department

Propagation delay Two types of propagation delay – tPLH , delay time in going from logical 0 to 1; tPHL delay from 1 to 0 ©2009, CE Department

Noise Immunity

Noise Immunity (cont.) The high state noise margin VNH is defined as VNH = VOH (min) – VIH (min) The low state noise margin VNL is defined as VNL = VIL (max) – VOL (max) ©2009, CE Department

Power Requirements Every IC need a certain power requirement to operate This power supply is come from the voltage supply that connected to the pin on the chip labeled VCC(TTL) or VDD(MOS) The amount of power require by ICs is determined by the current that it draws from the VCC The actual power is ICCxVCC ©2009, CE Department

Cont. ICC(avg) = (ICCH + ICCL)/2 PD(avg) = ICC(avg)Xvcc ©2009, CE Department

The TTL Logic Family FIGURE 8-7 (a) Basic TTL NAND gate; (b) diode equivalent for Q1. ©2009, CE Department

TTL NOR gate ©2009, CE Department

TTL Data sheet In 1964, Texas Instruments corporation introduced the first line of standard TTL ICs The 54/74 series, most widely used IC logic families The difference between 54 and 74 series is a range of temperatures IC number is the same with all series produce by different manufactures Each manufacturer however usually used the prefix that represent the special words – Texas Instrument uses the prefix SN, National semiconductor uses DM etc ©2009, CE Department

Supply Voltage and Temperature Range 74ALS series and the 54ALS series use nominal supply voltage (VCC) of 5V, but can tolerate a supply variation of 4.5 to 5.5V. 74ALS series can operate properly in ambient temperatures ranging from 0 to 70 degrees C, while the 54ALS series can handle -55 to +124 degree C. ©2009, CE Department

Voltage Levels Input and output voltage levels can be found on the data sheet. The min and max values shown are for worst case conditions of power supply, temperature and loading conditions

TTL Series Characteristics We have found the type of ICs – 74, 74LS, 74ALS before LS – low power Schottky, ALS – advance low power Schottky The function is same, but the difference is on the characteristic

TTL Data Sheet

TTL Series Characteristics 74 series of TTL – offers a wide variety of gates and flip flops Consist of: a. Standard TTL, 74 series – no longer be use b. Schottky TTL, 74S series c. Low-power Schottky TTL, 74LS Series d. 74AS e. 74ALS and 74F ©2009, CE Department

Schottky TTL, 74S Series 7400 series operates using saturated switching in which many of the transistors, when conducting will be in saturated condition This can causes a storage time delay ts when the transistors switch from ON to OFF and effect the speed 74S series come to solve the speed problem It accomplishes this by using a Schottky barrier diode (SBD) ©2009, CE Department

Schottky TTL, 74S Series (cont.) ©2009, CE Department

Advances Schottky TTL, 74AS series 74AS give more advance on speed switching of TTL ICs at much lower consumption The comparison is shown in the following table for a NAND gate in each series 74S 74AS Propagation delay Power dissipation Speed-power product 3ns 20 mW 60 pJ 1.7ns 8 mW 13.6 pJ ©2009, CE Department

Advanced Low Power Schottky TTL, 74ALS Series Improved on both speed and power dissipation 74S 74AS Propagation delay Power dissipation Speed-power product 9.5 ns 2 mW 19 pJ 4 ns 1.2 mW 4.8 pJ ©2009, CE Department

Example Use table 8-6 to calculate the dc noise margins for a typical 74LS IC. How does this compare with the standard TTL noise margins ? Solution 74LS VNH = VOH(min) – VIH(min) = 2.7 – 2.0 = 0.7 V ©2009, CE Department

TTL Loading and Fan Out ©2009, CE Department