Data conversion system with time division multiplexing

What is time division multiplexing?

Time division multiplexing means that each input channel is sequentially connected to the multiplexer for a certain time.(the input signals are not applied to the multiplexer continuously but are connected in turns to the multiplexer thereby sharing time in between them). The time of sharing the output is controlled by the unit called control unit. This control unit controls the sampling and hold circuits.

Importance of a D.C. system

D.C. systems are generally used for common resistance transducers such as potentiometer and resistance strain gauges. A.C. systems have to be used for variable reactance transducer and systems where signals have to be transmitted via long cables to connect the transducers to the signal conditioning equipment. After this physical quantities like temperature, pressure upon the system, strain in it, acceleration of the system during operation and many more have been transduced into their analogue electrical forms and amplified to a sufficient level of current and voltages. These levels can be generalized as 1 V to 10 V and they are further processed by electronic circuits. In some indicating or recording or may be control instruments. But many applications involves further processing of the signals which involves the linear and non linear operations, these have been mentioned earlier.

The input signal is applied to sampling and hold circuits which has been shown in the following figure with the help of circuit diagram and block diagram.

This may be fed to an analogue multiplexer and and analogue to digital convertor (called A/D convertor). Here it is to be mentioned that a multiplexer is and electronic device which make it possible to transmit a number of signal through a signal transmission line by the property of time sharing but under the control of control lines. There can mainly two types of multiplexer i.e. analogue and digital multiplexer as the name suggests analogue multiplexer multiplexes an analogue signal while in case of digital multiplexer the multiplexing is done with digital data i.e. a stream of 0s and 1s.

If the signal is in digital form it can be applied to a variety of digital systems this involves computers, digital controller, digital data logger or a digital data transmitter.

The figure which has been mentioned earlier is of an ideal sampling and hold circuit which samples the different inputs at a specific time and then hold the voltage levels at their output while analogue multiplexer performs the time division multiplexing (called TDM) operation between different data inputs.