12/8/2023 0 Comments Ttl 7432 transistor diagramCircuit (a), symbol (b), and Truth Table (c) of a simple inverting digital buffer. The arrowhead indicates the direction of signal flow, and the small circle on the symbol’s output indicates the inverting action.įIGURE 2. Figures 2 through 7 show a selection of very simple logic circuits that are designed around discrete components.įigure 2(a) shows a simple inverting digital buffer (also known as a NOT logic gate), consisting of an unbiased transistor wired in the common-emitter mode, and Figure 2(b) shows the international symbol that is used to represent it. Digital logic circuits come in a variety of basic types and can be built using a variety of discrete or integrated technologies. If a large sine-wave signal is connected to the input of this circuit, it produces an output that (ideally) is of purely digital form, as shown in Figure 1(b).ĭigital ICs are available in a variety of rather loosely defined categories such as memory ICs, electronic delay-line ICs, and microprocessor support ICs, etc., but the most widely used category is that known as the “logic” type, in which the ICs are designed around fairly simple logic circuits such as digital buffers, inverters, gates, or flip-flop elements. One simple type of digital IC element is the non-inverting buffer. Their outputs similarly have only two basic states, either low or high (logic-0 or logic-1). When a large input sine wave is fed to the input of a linear buffer (a), it produces a sine-wave output, but when fed to the input of a digital buffer (b), it produces a purely digital output. Digital ICs, on the other hand, are effectively blind to the precise amplitudes of their input signals, and simply recognize them as being in either a low or a high state (usually known as logic-0 and logic-1 states, respectively).įIGURE 1. If a large sine-wave signal is connected to the input of this circuit, it produces a low-impedance output of almost identical form and amplitude, as shown in Figure 1(a). One of the simplest types of linear IC elements is the unity-gain buffer. Linear ICs are widely used as pre-amplifiers, power amplifiers, oscillators, and signal processors, etc., and give a basic output that is directly proportional to the magnitude (analog value) of the input signal, which itself may have any value between zero and some prescribed maximum limit. ICs come in both “linear” and “digital” forms. An IC can be made fully functional by wiring it to a suitable power supply and connecting various pins to appropriate external input, output, and auxiliary networks. Digital Logic IC BasicsĪn IC can be described as a complete electronic circuit or “electronic building block,” integrated into one or more semiconductor slices (or “chips”) and encapsulated in a small, multi-pin package. This opening article concentrates on digital logic IC basics. This four-part mini-series explains the basic principles and usage rules of each of these three digital logic families, and provides practical usage guidance for the vast range of ICs available in each of these families. Each of these families has its own particular advantages and disadvantages, and its own special set of usage rules. Modern digital logic ICs are widely available in three basic types: TTL devices (typified by the 74LS00 logic family), “slow” CMOS devices (typified by the “4000” logic family), and “fast” CMOS devices (typified by the 74HC00 and 74AC00 logic families).
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