Upload
leigh-woodard
View
46
Download
0
Embed Size (px)
DESCRIPTION
Lecture 7: Z-Transform. Remember the Laplace transform? This is the same thing but for discrete-time signals! Definition: z is a complex variable:. imaginary. z. r. w. real. Z-transform. What is z -n or z n ? rate of decay (or growth) is determined by r - PowerPoint PPT Presentation
Citation preview
01-Oct, 98 EE421, Lecture 7 1
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Lecture 7: Z-Transform
Remember the Laplace transform? This is the same thing but for discrete-time signals!
Definition:
– z is a complex variable:
n
nznxzX )()(
sincos jrr
rez j
rz
real
imaginary
01-Oct, 98 EE421, Lecture 7 2
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-transform
What is z-n or zn?
– rate of decay (or growth) is determined by r– frequency of oscillation is determined by
njrnr
erznn
njnn
sincos
njrnr
erznn
njnn
sincos
real part imaginary part real part imaginary part
01-Oct, 98 EE421, Lecture 7 3
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
real
imaginary
unit circler = 1
plots of zn
01-Oct, 98 EE421, Lecture 7 4
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
Transfer function:
Notation:
Properties:– linearity– delay
– convolution
n
nznhzH )()(
system impulse response
)()( zXznnx 0nZ0
)()( zXnx Z
)()()()()()( zXzHzYnxnhny Z
01-Oct, 98 EE421, Lecture 7 5
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
Some simple pairs:– finite-length sequence
– impulse
321Z z3z1z213121
n=0
1zznn 0
n
nZ
)()(
01-Oct, 98 EE421, Lecture 7 6
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
The geometric series is important for deriving many z-transforms:
a1aa
a1NNN
Nn
n212
1
01-Oct, 98 EE421, Lecture 7 7
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
– unit step function
– reversed step function
10n
n
n
nZ
z11
zznunu
)()(
only if |Z|>1!
1
1
n
n
n
nZ
z11
zz1nu1nu
)()(
only if |Z|<1!
Do these different functions have the same z-transform?
01-Oct, 98 EE421, Lecture 7 8
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
Region of Convergence
In general, the z-transform is an infinite sum! This means it (the z-transform) may not exist for all values of z. More specifically, it is the value of r = |z| that is important. If x(n) = (0.5)nu(n), then
1
0n
n1
n
0n
n
z5011
z50
z50zX
.
).(
).()(
only if |Z|>0.5 !
0.5
z-plane
ROC
01-Oct, 98 EE421, Lecture 7 9
EE421, Fall 1998Michigan Technological University
Timothy J. Schulz
Z-Transform
Region of Convergence
Here’s what the ROC can look like:
|z|<a b<|z| b<|z|<a all |z|