[Maths Class Notes] on Z Transform Formula Pdf for Exam

In order to define z transform, it is simply a mathematical mechanism of going from the discrete time domain to the z domain also referred to as the complex frequency domain. Under the discrete time domain, a signal is generally described as a series of real or complex numbers which is then converted to the z-domain by the mechanism of z-transform.

Z Transform Formula

The formula applied in order to convert a discrete time signal x[n] to X[z] is as below:

X(Z)|z = e^jω = F. T[x(n)]

Where,

x[n] represents Finite length signal

[0, N] represents Sequence support interval

z  represents Any complex number

N represents Integer

X[z] represents the z-transform of the discrete time signal.

Now here is to notify that the z-transform comes in two parts. The first part is the formula as given above while the second part is to describe a region of convergence (ROC) for the z-transform. Both parts are required for a complete z-transform as a z-transform unaccompanied by ROC would not be of much assistance in signal processing. Moreover, though the z-transform is acquired by directly using this formula, the inverse z-transform needs some mathematical manipulations which are linked to the power series and geometric series.

Z Transformation Relation To Discrete-Time Fourier Transform (DTFT)

There is a close connection between DTFT and z-transform. In fact, each of their respective formulas are also pretty similar, which is most commonly overlooked. Thus, let’s take a look at the formulas for both the DTFT and the z-transform for a signal x[n].

A.   DTFT Formula:

ω = nω₀ and X(ω)=T_cn

B.   Z Transform Formula List

1. Bilateral Z Transform Formula

[X(z)=Zleft { x[n] right }=sum_{n=-infty}^{infty }x[n]z^{-n}] 

2. Unilateral Z Transform Formula

[X(z)=Zleft { x[n] right }=sum_{n=0}^{infty }x[n]z^{-n}]

Solved Z Transform Examples On How to Find Z Transform

Example: Express the z-transform for a finite series as given below.

x = {-2, -1, 1, 2, 3, 4, 5, 6, 7, 8}

Solution:

Known sequence of sample numbers x[n] = is x = {-2, -1, 1, 2, 3, 4, 5, 6, 7, 8}

Z-transform of x[n] can be mathematically expressed as:

X (z) = -2z0 – z-1 + z-2 + 2z-3 + 3z-4 + 4z-5 + 5z-6+ 6z-7+ 7z-8+ 8z-9

This can be further simplified as below.

X (z) = -2 – z-1 + z-2 + 2z-3 + 3z-4 + 4z-5 + 5z-6+ 6z-7+ 7z-8+ 8z-9