Delta modulation is basically analog to digital and a digital to analog signal conversion technique which is mainly used for data transfer. This type of modulation technique is used by the satellite business system, and it is also known as Differential pulse code modulation. This modulation technique is used to achieve high signal to noise ratio. Delta Modulation is basically of three types that are Adaptive Delta Modulation(ADM), Delta-sigma Modulation, and differential modulation. The ADM is a type of Delta Modulation in which the step size is variable, also known as continuously variable slope Delta Modulation.
What is Adaptive Delta Modulation?
Definition: This is a type of delta modulation technique. In digital modulation, there is a problem in determining the step size, which may have an influence on the quality of the wave, which is produced as output. We require a larger step size in the steep slope of the modulating signal, and a small step size is required when the message has a small slope. This kind of detail is ignored in Delta Modulation techniques. So, we need to have control over the step size according to our requirements so that we are able to obtain the sample output in the required fashion. This is the main concept behind adaptive Delta Modulation.
Block Diagram of ADM
The block diagram of adaptive delta modulation is shown below which includes an ADM transmitter & receiver. The transmitter has a summer, a quantizer, a delay circuit, and a logic circuit. Here, the step size is kept fixed between some predefined maximum and minimum values.
The upper limit is used to control the slope overload distortion and the lower limit is used to control the granular noise. The step size increase or decreases based on a certain set of rules.
The above figure represents an ADM receiver. The ADM receiver has two parts. The first part is used to produce the step size from the incoming bits. The bits are then applied to the second part of the receiver which contains an accumulator. The function of the accumulator is to build up the staircase waveform. The signal is then passed through a low pass filter which is used to smoothen the staircase waveform and reconstruct the original signal.
Adaptive Delta Modulation Theory
An Adaptive Delta Modulator is basically used to quantize the difference between the current signal value and the predicted value of the following signal. It uses variable step height in order to predict the consequent values. In ADM, the voltage gain which is controlled by the amplifier is adjusted by the output signal which is produced from the sampler.
The step size is determined by the amplifier gain. This is because the step size is proportional to the amplifier gain. So, we can say that ADM is basically a type of delta modulation. It is mainly used to overcome slope overload distortion and granular noises which occurs in delta modulation. Here, the step size of the quantifier varies according to the time.
Differences between Delta Modulation & Adaptive Delta Modulation
The differences between these two include the following.
- In delta modulation, the step size cannot be varied. It remains fixed for the entire signal. However, in the case of ADM, the step size can be varied according to the variation of the signal.
- In delta modulation, slope overload distortion and granular noise can be present but in ADM, quantization noise is present. The other types of errors are mainly avoided.
- This modulation utilizes the bandwidth a lot more efficiently as compared to that of delta modulation.
- It has a wider dynamic range than delta modulation.
The advantages of adaptive delta modulation include the following.
- This modulation can be used to reduce the slope error which is present in delta modulation.
- This can be used to remove the granular noises from the signal.
- It has an improved signal to noise ratio as compared to that of delta modulation.
- ADM has a low pass filter that can be used to remove the quantization noise.
- It has a higher dynamic range as compared to delta modulation.
There is no need for error detection in the case of adaptive delta modulation.
The applications of adaptive delta modulation include the following.
- It is effectively used in audio communications.
- It can be used in systems that require improved voice quality.
- It is used in voice coding.
- It is used in television signal transmission.
- The SECURENET line of Motorola uses 12kbit/sec adaptive delta modulation.
- It is used by NASA for different communications between spacecraft and mission control.
- The US Army also uses adaptive delta modulation in order to conserve bandwidth over various tactical links.
1). What is granular noise in Delta Modulation?
Granular noise is generated when the step size is quite large as compared to the variations in the input signal. It is basically the error between the approximated signal and the input signal. The problem of granular noise in delta modulation is rectified in adaptive delta modulation.
2). What is the advantage of delta modulation over PCM?
The major advantage of delta modulation as compared to that of PCM is that it provides the benefit of data delivery feedback to the transmitters. This increases the robustness of the signal.
3). What is the linear delta modulation?
Delta modulation is a digital modulation technique in which the signals can be encoded into a single bit. In the case of delta modulation, the step size is fixed. Hence, its maximum and minimum slopes will occur along a straight line. This type of modulation is called linear delta modulation.
4). What is step size in Delta Modulation?
The step size in delta modulation is basically the voltage difference between the present signal and the next signal.
5). What is slope overload in Delta Modulation?
Slope overload distortion is the distortion that occurs when there is a large dynamic range of the input signal. It is a major drawback of delta modulation.
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So, this was all about an overview of adaptive delta modulation. It is a modulation technique which is being used in recent times in various high-tech systems. This modulation technique is used to produce good quality output and it also enables fast encoding. In what other fields is the adaptive delta modulation technique used?