Delta Modulation & Demodulation Technique
A comprehensive guide to 1-bit quantization and efficient bandwidth utilization.
Delta Modulation Overview
Another name for delta modulation is a 1-bit quantizer. As a result, compared to PCM or DPCM, less bandwidth is needed here.
We know that bandwidth (BW):
Where:
- n = number of bits per sample
- fs = Frequency of Sampling
To avoid under-sampling, fs cannot be decreased to reduce bandwidth. We must maintain:
In delta modulation, bandwidth is minimized by picking the lowest possible value of n = 1 bit/sample.
If data rate Rb = nfs, then:
Bit rate = Pulse rate = Sampling rate
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Explore Modulation ToolsThe Modulation Process
Since we allocate 1 bit/sample, the number of levels is L = 2¹ = 2. The highest level is '+∆' and the lowest is '-∆'.
We compare the current sample value to the prior sample value. If the difference (error) exceeds the threshold, the output is '1'. If it falls below, the output is '0'.
Fig: Delta Modulation Block Diagram
Input of the quantizer:
Where:
- m(nTs) = current sample
- m^(nTs) = previous sample
Delta Demodulation
If the error value is between 0 and +∆ Volt, we convert it to bit '1'. For values between 0 and -∆ Volt, we translate to bit '0'.
Fig: Diagram of DM Quantizer
Fig: DM Encoder System
Decoding Process Logic
In the decoding process, we track the summation of current and previous samples:
At t = Ts: 0 + ∆ = +∆
At t = 2Ts: +∆ + ∆ = +2∆
At t = 3Ts: +2∆ + ∆ = +3∆
At t = 4Ts: +3∆ - ∆ = +2∆
At t = 5Ts: +2∆ - ∆ = +∆
Fig: DM Decoder at Receiver Side
Fig: Staircase Waveform Reconstruction
