Delta modulation, delta-sigma modulation, and adaptive delta modulation are analog-to-digital conversion techniques. Delta modulation samples an input signal and outputs a single bit indicating the sign of the difference between samples. It has higher SNR than other techniques but can suffer from slope overload and granular noise. Delta-sigma modulation places an integrator between the source and quantizer, reducing quantization error and more closely matching the original wave. Adaptive delta modulation uses a variable step size to better handle rapidly changing slopes and slow changes, improving quality.

1. Delta, Delta-Sigma, and
Adaptive Delta Modulation
and Demodulation
JEREMY RUPPERT
AUBURN UNIVERSITY

2. 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.

3. 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.

4. 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.

5. Delta Modulation
Demodulated Delta Signal:
• Input speech message  Yellow
• Demodulated message  Green
Visible noise difference
between original message and
demodulated message

6. 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

7. 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

8. Delta Modulation
Original Message Delta Modulated

9. 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

10. 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

11. Delta-Sigma Modulation
Demodulated Delta–Sigma Signal:
• Input speech message  Yellow
• Demodulated message  Green

12. Delta-Sigma Modulation
Original Message Delta-Sigma Modulated

13. 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.

14. Adaptive Delta Modulation
 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

15. Adaptive Delta Modulation
Demodulated Adaptive Delta Signal
• Input speech message  Yellow
• Demodulated message  Green

16. Adaptive Delta Modulation
Original Message Adaptive Delta Modulated

17. Summary and Comparison of Noise
Delta sigma modulationDelta modulation Adaptive delta modulation

18. Sources
• http://www.ni.com/white-paper/11342/en/
• http://www.ti.com/lit/an/slyt423/slyt423.pdf
• http://electronicdesign.com/analog/understandi
ng-delta-sigma-modulators
• http://www.eng.auburn.edu/~troppel/courses/TI
MS-manuals-
r5/TIMS%20Experiment%20Manuals/Student_Te
xt/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