Digital Electronics and Logic Circuit Md. Ebtidaul Karim

References Digital Logic and Computer Design M. Morris Mano Modern Digital Electronics R.P. Jain

Digital Electronics Digital electronics or digital (electronic) circuits are electronics that operate on digital signals. These are discrete signals which are sampled from analog signal. Digital circuits use binary notation for transmission of signal. For Example, a continuous analog audio signal is sampled and converted to Boolean algebra that is, 1’s and 0’s format to be transmitted over digital circuit. High Level Signal: 1 (5V) Low Level Signal: 0 (0V)

Digital Electronics

Digital Electronics Disadvantages: Digital Circuits operate only with digital signals hence, encoders and decoders are required for the process. This increases the cost of equipment. Energy consumption in digital circuit is more than analog circuit for same calculation or signal processing. Production of heat is more due to higher energy consumption. For smaller circuits Digital Circuits are comparatively expensive. Real world is analogue in nature, all quantities such as light, temperature, sound etc. For Digital Systems it is required to translate a continuous signal to discrete which leads to small quantization errors. To reduce quantization errors large amount of data needs to be stored in Digital Circuit.

Sequential Circuit It consists of a combinational circuit to which memory elements are connected to form a feedback path. Now what is combinational circuit??? Combinational circuit is a circuit whose output is dependent only on the state of its inputs. Memory elements are devices capable of storing binary information within them. The binary elements at any given time defines the state of the sequential circuit.

Sequential Circuit

Sequential Circuit Sequential circuit receives binary information from external inputs. These inputs, together with the present state of the memory elements, determine the binary value at the output terminals. The next state of memory element is also a function of external inputs and the present state. Thus a sequential circuit is specified by a time sequence of input, output and internal states.

Classification There are mainly two types of sequential circuit, such as: Synchronous Sequential Circuit Asynchronous Sequential Circuit In synchronous sequential circuit output changes after e certain interval. In synchronous sequential circuits, the state of device changes at discrete times in response to a clock signal. In asynchronous circuits, the state of the device changes in response to changing inputs. Here there is nothing to control time

Classification Synchronization is achieved by a timing device called master clock generator, which generates a periodic train of clock pulse. Clock pulses are applied into AND gates together with the signals that specify the required change in memory elements. Synchronous sequential circuit that use clock pulse in the inputs of the memory elements are known as called sequential circuit. Fig: Clock Signal

Flip Flops The memory element used in clocked sequential circuits are called flip flops. These circuits are binary cell capable of storing one bit of information. It has two outputs. One for the normal value and one for the compliment value of the bit stored in it. A flip flop circuit can maintain a binary state indefinitely, (as long as the power is delivered to the circuit) until directed by an input signal to switch stages. Fig: Clocked Sequential Circuit

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