Principles of communication
The sampling frequency of a signal should be higher than the Nyquist frequency, to obtain better sampling. If this sampling interval in a differential PCM (DPCM) is drastically reduced, the sample-to-sample amplitude difference is very small, as if the difference is 1-bit quantization , then the size not very small, that is to say Δ (delta).
What is Delta modulation?
The type of modulation, where the sampling frequency is much higher and the step after quantization is smaller Δ , such modulation is called delta modulation .
Characteristics of delta modulation
An oversampled input is used to make full use of signal correlation.
The quantization design is simple.
The input sequence is much higher than the Nyquist rate.
The quality is average.
The design of the modulator and demodulator is simple.
The stepped approximation of the output waveform.
The step size is very small, that is Δ (delta).
The bit rate can be decided by user.
This requires a simpler implementation.
Delta modulation is a simplified form of the DPCM Technique, also considered a 1-bit DPCM scheme. When the sampling interval is reduced, the signal correlation will be higher.
The Delta Modulator includes a 1 bit quantizer and a delay circuit with two summer circuits. Here is the block diagram of a delta modulator.
An approximate waveform in a cage of 'stair will be the output of the delta modulator with the step size in delta ( Δ ). The quaThe output unit of the waveform is medium.
The delta demodulator includes a low step filter, a summer and a delay circuit. The predictor circuit is eliminated here and therefore no assumed input is given to the demodulator.
Here is the block diagram of the delta demodulator.
The low pass filter is used for many reasons , but the main one is noise eliminating out-of-band signals. The step size error that can occur at the transmitter is called granular noise , which is eliminated here. 'there is no noise, then the output of the modulator is equal to the input of the demodulator.
Advantages of DM over DPCM
- 1 bit quantizer
- Very simple design of modulator and demodulator
However, there is some noise in DM and here are the noise types.
- Slope Overload distortion (when Δ is small)
- Granular noise (when Δ is largeand)
Adaptive Delta Modulation
In digital modulation, we have some problems in determining the step size, which influences the quality of the output wave .
The larger step size is needed in the steep slope of the modulation signal and a smaller step is needed when the message has a small slope. As a result, the smallest details are missed. Therefore, it would be better if we could control the adjustment of the step size, according to our need in order to get the sampling in the desired way. This is the concept of Adaptive Delta Modulation (ADM) .