LinearDigital ICs

1
Linear-Digital ICs

• By
• Marlou Jake E. Montaño
• BSCS-4

2
Introduction

• The Linear or Digital ICs
• - Comparator Units
• - Digital / Analog Converters
• - Interface Circuits
• - Timer Circuits
• - Voltage-Controlled Oscillator (VCO)
• - Phase-Locked Loops

3
Comparator Circuit

• one to which a linear input voltage is
• compared to another reference voltage.
• the output being a digital condition
• representing whether the input voltage
• exceeded the reference voltage.

4
Digital / Analog Converters

• circuits that convert digital signals into
• an analog or linear voltage.
• convert a linear voltage into a digital
• value.
• aerospace and automotive equipment
• and compact disk (CD) players.

5
Interface Circuits

• used to enable connecting signals of
• different digital voltage levels from
• - different types of output devices
• - different impedances
• so that both the driver stage and the
• receiver stage operate properly.

6
Timer Circuits

• provide linear and digital circuits to use
• in various timing operations
• - car alarm
• - home timer
• - circuit in electromechanical
• equipment.
• to provide proper timing to match the
• intended unit operation.

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Voltage-Controlled Oscillator

• provides an output clock signal whose
• frequency can be varied or adjusted by
• an input voltage.
• popular application is in phase-locked
• loop units.

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Phase-Locked Loops (PLLs)

• an electronic circuit that consist of a
• phase detector.
• used in various communication
• transmitters and receivers
• - frequency demodulation
• - frequency synthesis
• - FSK (Frequency-Shift Keyed)
• decoders

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Comparator Unit Operation

• a comparator circuit accepts input of
• linear voltages and provides a digital
• output that indicates when one input
• is less than or greater than the second.

10
V
V (10 V)
Vref (2V)
- input
output
output
input
Vin
( a )
( b )
-V
-V (-10 V)

• Figure 1 Comparator Unit
• Basic unit
• - the output is a digital signal that stays
  at high voltage level when the non-inverting
• (-) input, and switches to a lower voltage
  level when the non-inverting input voltage
• goes below the inverting input voltage.
• (b) Typical application
• - shows a typical connection with one input
  connected to a reference voltage level of
• 2 V, the output remains at a low voltage
  level (near -10 V).

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Vo
V
Vsat
2
7
t
6
Output, Vo
3
-Vsat
Input, Vi
4
( b )
( a )
V-
Figure 2 Operation of 741 op-amp as comparator
With reference input (at pin 2) set to 0 V, a
sinusoidal signal applied to the
noninverting input (pin3) will cause the output
to switch between its two output states, as shown
in figure (b). The input Vi going even a fraction
of a millivolt above the 0-V reference level will
be amplified by the very high voltage gain
(typically over 100,000) so that the
output arises to its positive output saturation
level and remains there while the input stays
above Vref 0 V. When the input drops below the
0 V reference level, the output is driven to
its lower saturation level and stays there while
the input remains below Vref 0 V. In general
use, the reference level need not be 0 V but can
be any desired positive or negative voltage.
Also, the reference voltage may be connected to
either plus or minus input and the input signal
then applied to the other input.
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Use of Op-Amp as Comparator
12 V
Figure 3 ( a )
10 k?
10 k?
Vi
470 ?
-12 V
LED on when Vi goes above Vref ( 6 V )
LED
Figure 3 ( a ) shows a circuit operating
with a positive reference voltage connected to
the minus input and the output connected to an
indicator LED. The reference voltage is set at
Vref
10 k?
(12 V) 6 V
10 k? 10 k?
13
Use of Op-Amp as Comparator
12 V
10 k?
Figure 3 ( b )
Vi
Vo
10 k?
470 ?
-12 V
LED on when Vi goes below Vref ( 6 V )
LED
Figure 3 ( b ) With this connection the
input signal going below the reference level
would cause the output to drive LED on. The LED
can thus be made to go on when the input signal
goes above or below the reference level,
depending on which input is connected as signal
input and which as reference input.