introduction to digital signal processing n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
INTRODUCTION TO DIGITAL SIGNAL PROCESSING PowerPoint Presentation
Download Presentation
INTRODUCTION TO DIGITAL SIGNAL PROCESSING

Loading in 2 Seconds...

play fullscreen
1 / 16

INTRODUCTION TO DIGITAL SIGNAL PROCESSING - PowerPoint PPT Presentation


  • 95 Views
  • Uploaded on

INTRODUCTION TO DIGITAL SIGNAL PROCESSING. Dr. Hugh Blanton ENTC 4347. TOPICS. Impact of DSP Analog vs. digital: why, what & how Digital system example Sampling & aliasing ADCs: performance & choice Digital data formats. Limitations. Advantages.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'INTRODUCTION TO DIGITAL SIGNAL PROCESSING' - niveditha


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
topics
TOPICS
  • Impact of DSP
  • Analog vs. digital: why, what & how
  • Digital system example
  • Sampling & aliasing
  • ADCs: performance & choice
  • Digital data formats

Dr. Blanton - ENTC 4347 - From analog to digital domain 2 / 30

digital vs analog

Limitations

Advantages

  • A/D & signal processors speed: wide-band signals still difficult to treat (real-time systems).
  • Finite word-length effect.
  • Obsolescence (analog electronics has it, too!).
  • More flexible.
  • Often easier system upgrade.
  • Data easily stored.
  • Better control over accuracy requirements.
  • Reproducibility.
Digital vs Analog

Digital Signal Processing

Dr. Blanton - ENTC 4347 - From analog to digital domain 3 / 30

impact of dsp on modern living
Impact of DSP on Modern Living

Cellular/mobile telephony Speech and channel coding Voice and data processing Power management Multipath equaliztion

Digital audio Stereo and surround sound Audio equalization and mixing Electronic music

Medical electronics Critical/intensive care monitors Digital X-rays ECG analyzers Cardiac monitors Medical imaging

Automotive Digital Audio Digital Radio Personal communication systems Active suspension

Personal computer Sound cards Data storage and retrieval Error correction/concealment Multimedia Modems

Dr. Blanton - ENTC 4347 - From analog to digital domain 4 / 30

analog digital signals

Analog

Digital

Discrete function Vk of discrete sampling variable tk, with k = integer: Vk = V(tk).

Continuous function V of continuous variable t (time, space etc) : V(t).

Uniform (periodic) sampling. Sampling frequency fS = 1/ tS

Analog & digital signals

Dr. Blanton - ENTC 4347 - From analog to digital domain 5 / 30

dsp aim tools

Predicting a system’s output.

  • Implementing a certain processing task.
  • Studying a certain signal.

Applications

  • General purpose processors (GPP), -controllers.
  • Digital Signal Processors (DSP).
  • Programmable logic ( PLD, FPGA ).

Hardware

Fast

Faster

real-time DSPing

  • Programming languages: Pascal, C / C++ ...
  • “High level” languages: Matlab, Mathcad, Mathematica…
  • Dedicated tools (ex: filter design s/w packages).

Software

DSP: aim & tools

Dr. Blanton - ENTC 4347 - From analog to digital domain 6 / 30

digital system example

General scheme

ANALOG DOMAIN

FilterAntialiasing

FilterAntialiasing

Sometimes steps missing

- Filter + A/D

(ex: economics);

- D/A + filter

(ex: digital output wanted).

A/D

A/D

DIGITAL DOMAIN

Digital Processing

Digital Processing

D/A

ANALOG DOMAIN

Topics of this lecture.

FilterReconstruction

Digital system example

Dr. Blanton - ENTC 4347 - From analog to digital domain 7 / 30

digital system implementation

ANALOG INPUT

Antialiasing Filter

1

2

3

A/D

Digital Processing

• Digital format.

What to use for processing?

See slide “DSPing aim & tools”

DIGITAL OUTPUT

Digital system implementation

KEY DECISION POINTS:

Analysis bandwidth, Dynamic range

•Sampling rate.

• Pass / stop bands.

• No. of bits. Parameters.

Dr. Blanton - ENTC 4347 - From analog to digital domain 8 / 30

sampling

1

*

Ex: train wheels in a movie.

25 frames (=samples) per second.

Train starts wheels ‘go’ clockwise.

Train accelerates wheels ‘go’ counter-clockwise.

*Sampling: independent variable (ex: time) continuous  discrete.

Quantisation: dependent variable (ex: voltage) continuous  discrete.

Here we’ll talk about uniform sampling.

Sampling

How fast must we sample a continuous signal to preserve its info content?

Why?

Frequency misidentification due to low sampling frequency.

Dr. Blanton - ENTC 4347 - From analog to digital domain 9 / 30

sampling 2

1

__ s(t) = sin(2f0t)

s(t) @ fS

f0 = 1 Hz, fS = 3 Hz

__ s1(t) = sin(8f0t)

__ s2(t) = sin(14f0t)

s(t) @ fS represents exactly all sine-waves sk(t) defined by:

sk (t) = sin( 2 (f0 + k fS) t ) , k 

Sampling - 2

Dr. Blanton - ENTC 4347 - From analog to digital domain 10 / 30

the sampling theorem

1

Example

Condition on fS?

F1

F2

F3

fS > 300 Hz

F1=25 Hz, F2 = 150 Hz, F3 = 50 Hz

fMAX

The sampling theorem

A signal s(t) with maximum frequency fMAX can be recovered if sampled at frequency fS > 2 fMAX .

Theo*

*Multiple proposers: Whittaker(s), Nyquist, Shannon, Kotel’nikov.

Naming gets

confusing !

Nyquist frequency (rate) fN = 2 fMAXor fMAXor fS,MINor fS,MIN/2

Dr. Blanton - ENTC 4347 - From analog to digital domain 11 / 30

frequency domain hints

1

Example

Ear + brain act as frequency analyser: audio spectrum split into many narrow bands low-power sounds detected out of loud background.

  • Bandwidth: indicates rate of change of a signal. High bandwidth signal changes fast.

BOOM !

minus 50 Hz ??

Frequency domain (hints)
  • Time & frequency: two complementary signal descriptions. Signals seen as “projected’ onto time or frequency domains.

Warning: formal description makes use of “negative” frequencies !

Dr. Blanton - ENTC 4347 - From analog to digital domain 12 / 30

sampling low pass signals

1

(a)Band-limited signal:

frequencies in [-B, B] (fMAX = B).

(a)

(b)

(b)Time sampling frequency repetition.

fS > 2 B no aliasing.

(c)

(c)fS 2 B aliasing !

Aliasing: signal ambiguity in frequency domain

Sampling low-pass signals

Dr. Blanton - ENTC 4347 - From analog to digital domain 13 / 30

antialiasing filter

1

(a)

(a),(b)Out-of-band noise can aliase into band of interest. Filter it before!

(c)Antialiasing filter

(b)

  • Passband: depends on bandwidth of interest.
  • Attenuation AMIN : depends on
  • ADC resolution ( number of bits N).
  • AMIN, dB ~ 6.02 N + 1.76
  • Out-of-band noise magnitude.
  • Other parameters: ripple, stopband frequency...

(c)

Antialiasing filter

Dr. Blanton - ENTC 4347 - From analog to digital domain 14 / 30

under sampling hints

1

m , selected so that fS > 2B

Example

Advantages

  • Slower ADCs / electronics needed.
  • Simpler antialiasing filters.

fC = 20 MHz, B = 5MHz

Without under-sampling fS > 40 MHz.

With under-sampling fS = 22.5 MHz (m=1);

= 17.5 MHz (m=2); = 11.66 MHz (m=3).

Under-sampling (hints)

Using spectral replications to reduce sampling frequency fS req’ments.

Dr. Blanton - ENTC 4347 - From analog to digital domain 15 / 30

over sampling hints

1

Oversampling : sampling at frequencies fS >> 2 fMAX .

Over-sampling & averaging may improve ADC resolution

( i.e. SNR, see )

fOS = over-sampling frequency,

w = additional bits required.

2

fOS = 4w· fS

Each additional bit implies over-sampling by a factor of four.

Caveat

  • It works for:
  • white noise with amplitude sufficient to change the input signal randomly from sample to sample by at least LSB.
  • Input that can take all values between two ADC bits.
Over-sampling (hints)

Dr. Blanton - ENTC 4347 - From analog to digital domain 16 / 30