PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

570 Practical MATLAB® Applications for Engineers

The OA is basically a voltage amplifi er with a large open-loop gain (about 10^6 ), a

large input impedance (about 2 MΩ), and a small output impedance (about 75 Ω).

The symbol used to represent an OA as well as its typical electrical specs are indi-

cated in Figure 6.5.

R.6.44 Digital fi lters, in contrast, use digital processors to perform numerical operations
on a sequence of discrete (sampled) values representing an analog signal.
The processor can be a powerful computer, a personal computer (PC), or a digital
signal processing (DSP) special chip.
Samplers, analog-to-digital converters and encoders, are used to convert and pro-
cess the analog signal into a discrete signal.
This signal is then represented by a sequence of numbers that are stored and then
processed.

R.6.45 Some of the key features that distinguish digital from analog fi lters are summa-
rized as follows:
Digital fi lters are programmable.
Digital fi lters are implemented using software packages.
Digital fi lters can easily be changed or updated without affecting their cir-
cuitry (hardware).
Digital fi lters can be designed, tested, and implemented on a general-purpose
computer.
Digital fi lters are independent of physical variables such as temperature, toler-
ances of elements, noise, fl uctuations, or interference.
Analog fi lters use elements that are environment dependent, and any fi lter
change is usually hard to implement and a complete redesign is often required.

R.6.46 Let us get back to the normalized passive fi rst-order fi lters. Some simple implemen-
tations of LPF are shown in Figure 6.6.

• • • • • •

FIGURE 6.5
The operational amplifi er.

1

2

Vi(w)^3

Vo(w)

Zo

Zi

OA

Voltage gain = 200,000 (106 db)

Zo = 75 Ω

Zi = 2 MΩ

Output voltage swing = +13 V, − 13 V

Small signal BW = 1 MHz

FIGURE 6.6
Normalized passive fi rst-order LPF.

R = 1 Ω

C = 1 F R = 1 Ω

L = 1 H

Vi(s) Vo(s) Vi(s) Vo(s)

H(s) = Vo(s)

Vi(s)

=^1

s+1

The transfer function of either circuit is