Advantages of Delta Modulation
The delta modulation has certain advantages over PCM as under :
- Since, the delta modulation transmits only one bit for one sample, therefore the signaling rate and transmission channel bandwidth is quite small for delta modulation compared to PCM .
- The transmitter and receiver implementation is very much simple for delta modulation. There is no analog to digital converter required in delta modulation.
Disadvantages of Delta Modulation
The delta modulation has two major drawbacks as under :
- Slope overload distortion
- Granular or idle noise
Now, we will discuss these two drawbacks in detail.
Slope Overload Distortion
This distortion arises because of large dynamic range of the input signal.
We can observe from fig.1 , the rate of rise of input signal x(t) is so high that the staircase signal can not approximate it, the step size ‘Δ’ becomes too small for staircase signal u(t) to follow the step segment of x(t).
Hence, there is a large error between the staircase approximated signal and the original input signal x(t).
This error or noise is known as slope overload distortion .
To reduce this error, the step size must be increased when slope of signal x(t) is high.
Since, the step size of delta modulator remain fixed, its maximum or minimum slopes occur along straight lines. Therefore, this modulator is known as Linear Delta Modulator (LDM) .
2. Granular or Idle Noise
Granular or Idle noise occurs when the step size is too large compared to small variation in the input signal.
This means that for very small variations in the input signal, the staircase signal is changed by large amount (Δ) because of large step size.
Fig.1 shows that when the input signal is almost flat , the staircase signal u(t) keeps on oscillating by ±Δ around the signal.
The error between the input and approximated signal is called granular noise.
The solution to this problem is to make the step size small .