Continuous time signal, Discrete time signal and Digital signal

Definitions of Continuous time signal , Discrete time signal  and Digital signal

• Continuous Time Signal: In Continuous time signal output value (Dependent variable value e.g. Amplitude) is continuous with respect to Independent variable i.e. time for time signal. Output occurs for each and every value of input variable time (t tends form – ∞ to +∞). It is also called Analog Signal. Continuous time signal is represented as:

        X(t)= exp(-5t)u(t) ;    Where u(t) is unit step function.

•   Discrete Time signal: In discrete time signal output value (Dependent variable value e.g. Amplitude) is continuous with respect to Independent variable i.e. time. But here time is discrete i.e. time axis is not continuous. The discrete time signal is obtained by sampling a continuous time signal with standard sampling techniques. E.g. Nyquist sampling technique. Discrete Time signals are represented as :

       X(nTs) = exp(-5[nTs]) or X(n) = exp(-5[n])   ; if Ts = 1.

• Digital Signal: A digital signal defined as the signal whose both Independent Variable (Time axis) and dependent variable (e.g. Amplitude) have finite discrete levels. Time axis is discretised with standard sampling technique and also amplitude or output is discretizing with quantization technique. Generally Output variable have few discrete quantize levels.  And Independent variable may have more no of discrete level. Digital signal are generally represented in binary coding. Each Output quantize level is represented with a unique binary code. i.e. if output is quantize to 256 discrete levels the each level is represented with 8 bit long bit sequence e.g. 10010100 = X(n).