NI Presenation Delta

Delta, Delta-Sigma, and Adaptive Delta Modulation and DemodulationJEREMY RUPPERT

AUBURN UNIVERSITY

First, a few definitions…

An analog to digital converter (ADC) changes an analog signal into a digital one. Some examples: voice, temperature, pressure

A quantizer takes a set of input values and maps it to a smaller set of values, usually a predetermined range of voltages.

A limiter is a circuit that allows signals below a specified input power or level to pass unaffected while attenuating the peaks of stronger signals that exceed this threshold to prevent distortion.

Sampling is the reduction of a continuous time signal to a discrete signal, a sequence of quantities.

Pulse code modulation is sampling an analog signal to derive a data stream, a series of 1s and 0s.

Delta Modulation

An analog-to-digital and digital-to-analog signal conversion technique

Simplest form of differential pulse-code modulation (DPCM)

Periodically samples the input message, to make a comparison of the current sample with that preceding it, and outputs a single bit which indicates the sign of the difference between the two samples.

Delta Modulation

Delta Modulated Signal• Note the saw-tooth waveform

• Transmitted data is reduced to a 1-bit data stream.• Each segment of the approximated signal is

compared to the original analog wave to determine the increase or decrease in relative amplitude.

Delta Modulation

Demodulated Delta Signal:

• Input speech message Yellow• Demodulated message Green

Visible noise difference between original message and demodulated message

Delta Modulation - Advantages

SNR – Delta modulation gives a higher signal-to-noise ratio than other conventional modulation techniques

Bandwidth - lower channel bandwidth consumption. Sending one binary bit as a carrier pulse with one sample of digitized data lowers the bandwidth of the transmission channel

Simple circuitry – adder, integrator, quantizer, LPF for demodulation

Delta Modulation - Disadvantages

Slope overload - If the input signal is rising or falling with a slope larger than Δ/T, where T is the sampling time, we say that the sampler is suffering from slope overload.

Granular noise –the output signal must always either increase by a step, or decrease by a step, and cannot stay at a single value. This means that if the input signal is level, the output signal could be oscillatory.

Increased step size to alleviate slope overload

Delta Modulation

Original Message Delta Modulated

Delta-Sigma Modulation

Delta-Sigma Modulated Signal• More closely related to the original wave

Places an integrator in between the source and the summer which obviates the need for an integrator at demodulation, so the demodulator can be a simple LPF.

Adaptation of step size

Delta-Sigma Modulation Advantages

Attempts to alleviate avoid slope overload, reducing quantization error.

Resulting analog signal then added to the input signal

Reduces error introduced by the delta-modulation.

Used in modern electronics

Converters, switched-mode power supplies, motor controllers

Also used in some high-performance data-acquisition devices


Demodulated Delta–Sigma Signal:



Original Message Delta-Sigma Modulated

Adaptive Delta Modulation

Adaptive Delta Modulated Signal

A large step size was required when sampling those parts of the input waveform of steep slope. But a large step size worsened the granularity of the sampled signal when the waveform being sampled was changing slowly. A small step size is needed for when the slope is changing quickly.


Allows for a controllable step size to be implemented

Continuous Variable Slope Delta Modulation (CVSDM)

Encodes the difference between predicted samples and speech samples

Provides a more efficient comparison and reduction in the number of bits per sample.

Commonly used in short-range wireless digital voice transmission for its low implementation cost and robustness in dealing with bit errors


Demodulated Adaptive Delta Signal



Original Message Adaptive Delta Modulated

Summary and Comparison of Noise

Delta sigma modulationDelta modulation Adaptive delta modulation

Sources

• http://www.ni.com/white-paper/11342/en/

• http://www.ti.com/lit/an/slyt423/slyt423.pdf

• http://electronicdesign.com/analog/understanding-delta-sigma-modulators

• http://www.eng.auburn.edu/~troppel/courses/TIMS-manuals-r5/TIMS%20Experiment%20Manuals/Student_Text/Vol-D1/D1-13.pdf

• http://www.eng.auburn.edu/~roppeth/courses/TIMS-manuals-r5/TIMS%20Experiment%20Manuals/Student_Text/Vol-D1/D1-16.pdf

• http://www.eng.auburn.edu/~roppeth/courses/TIMS-manuals-r5/TIMS%20Experiment%20Manuals/Student_Text/Vol-D1/D1-15.pdf

Documents

NI Presenation Delta