konversi data analog ke digital - dina maizana

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Konversi Data analog ke digital

Dr Ir Dina Maizana MT

[email protected]

Mari kita berdoa menurut agama dan kepercayaan masing-masing sebelum kelas dimulai.

Doa dimulai…

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Jadwal Kandungan Jam

Minggu-1 Pendahuluan, penyampaian kontrak kuliah, Konsep-konsep pengukuran, Kesalahan-kesalahan pembacaan alat ukur

Selasa (9.40-12.10 wib) R. III.3 Selasa (19.00-20.30 wib) R. A.II.6

Minggu-2 Satuan pengukuran dan besaran standar listrik, Nilai dan fungsi satuan

Minggu-3 Besaran listrik, Alat ukur dengan termokopel, besi putar, elektrodinamis, elektrostatis dan induksi.

Minggu-4 Instrument penunjuk arus searah, Volt Ammeter DC, Prinsip kerja, Cara kerja, Penggunaan alat ukur DC

Minggu-5 Instrument arus bolak-balik, Voltmeter elektrostatis, Prinsip Kerja,Cara kerja, Penggunaan alat ukur untuk AC

Minggu-6 Pengukuran daya, Wattmeter, Pengukuran daya tanpa Wattmeter, Type alat pengukur daya

Minggu-7 Penggunaan jembatan Wheatstone, Prinsip dari jembatan wheatstone, Contoh dari jembatan wheatstone

Minggu-8 UTS

Minggu-9 Pengukuran dengan alat ukur oscilloscope

Minggu-10 Generator sinyal

Minggu-11 Alat-alat ukur digital

Minggu-12 Trafo Instrumentasi, Trafo arus untuk alat ukur, Trafo tegangan alat ukur, Kwh meter.

Minggu-13 Transduser

Minggu-14 Konversi Data analog ke digital

Minggu-15 Sistem data akusisi

Minggu-16 UAS

Rencangan Pembelajaran Semester (RPS) Sem. A ta 2019/20

CPMK

Mahasiswa mampu menjelaskan Konversi Data analog ke digital

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PRINCIPLES OF DATA CONVERSION OUTLINE

Signal vs data

Digital to Analog Data Convertor (DAC)

-Binary Weighted Resistor

-R-2R Ladder

Analog to Digital Data Convertor(ADC)

-Digital-Ramp ADC

-Successive Approximation ADC

-Flash ADC

Voltage to Frenquency Converter

Frequency to Voltage Converter

Digital instruments

Is more advantages in term of speed, increased accuracy, resolution, reduction in error and the ability to provide automatic measurement in system application

Analog to Digital

Converter

Signal Processing

Display

(Building block of a digital instrument)

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Comparison of digital and analog instruments

Digital instruments are basically the arrangement of logic circuit while the analog is base on fundamental circuit

The comparison of digital and analog instruments are shown in table below

Digital Instruments Analog Instruments

-the outputs are in digital data

-easy to read and to analyze

-more accurate

-the range is more wider

-it has better resolution

-build with triggering circuits

that used for sample speed (3

to 10 samples per second)

-able to read beyond full scale

-the outputs are in analog data

-need to read the analog scale

properly and must has skill to

process the data

-not too accurate

-the range is not wider

-low resolution

-low sample speed with 1 sample

per 1sec or 2sec

Analog and Digital Signals

• Signals can be analog or digital. • Analog signals can have an infinite number of values in a

range. • Digital signals can have only a limited number of values.

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Analog and Digital Data

Data can be analog or digital. Analog data are continuous and take continuous values. Digital data are discrete and take discrete values.

Comparison of analog and digital signals

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• A number may be represented in digital form by simply setting a pattern of voltages on a line high or low. An 8 bit binary pattern is shown below.

Revision of Binary Number

BIT NUMBER 7(28) 6(27) 5(26) 4(25) 3(24) 2(22) 1(21) 0(20)

BIT VALUE 128 64 32 16 8 4 2 1

• Bit zero is called the least significant bit (LSB) and the bit with highest value is called the most significant bit (MSB).

Digital to Analog Data Conversion

1. DAC

What is a DAC? A digital to analog converter (DAC) converts a digital

signal to an analog voltage or current output.

DAC 100101…

input

output

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In an electronic circuit, a combination of high voltage (e.g. +5V) and low voltage (0V) is usually used to represent a binary number. For example, a binary number 1010 is represented by

Weighting

23

22

21

20

Binary Digit

1

0

1

0

State

+5V

0V

+5V

0V


DACs are used in many other applications, such as voice synthesizers, automatic test system, and process control actuator. In addition, they allow computers to communicate with the real (analog) world.

Reg

iste

r

Voltage

Switch

Resistive

Summing

NetworkAmplifier

Input Binary

Number

Analog Voltage

Output

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Digital to Analog Data Conversion Register: Use to store the digital input (let it remain a constant value) during the conversion period. Voltage switch: Similar to an ON/OFF switch. It is ‘closed’ when the input is ‘1’. It is ‘opened’ when the input is ‘0’. Resistive Summing Network: Summation of the voltages according to different weighting. Amplifier: Amplification of the analog according to a pre-determined output voltage range. For example, an operation amplifier

Types of DACs

Many types of DACs available.

Usually switches, resistors, and op-amps used to implement conversion

Two Types:

Binary Weighted Resistor

R-2R Ladder

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Utilizes a summing op-amp circuit

Weighted resistors are used to distinguish each bit from the most significant to the least significant

Transistors are used to switch between Vref and ground (bit high or low)


-

+

R

2R

4R

2nR

Rf

Vout

I

Vref MSB

LSB

Assume Ideal Op-amp

No current into op-amp

Virtual ground at inverting input

Vout= -IRf

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R

V

R

V

R

V

R

VRIRV

1-n

n321ffout

242

MSB

LSB

I

-

+

R

2R

4R

2n-1R

Rf

Vout

Vref

V1

V2

V3

Vn

MSB

LSB

Voltages V1 through Vn are either Vref if corresponding bit is high or ground if corresponding bit is low V1 is most significant bit (MSB) Vn is least significant bit (LSB)


If Rf=R/2

n

n321fout

2842

VVVVIRV

For example, a 4-Bit converter yields

16

1

8

1

4

1

2

10123refout bbbbVV

Where b3 corresponds to Bit-3, b2 to Bit-2, etc.

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Example 1

Calculate the value of Vo, of a 4-bit weighted –resistor DAC, where Vref = 5V, R = 1kΩ, Rf = 470 Ω, and digital input of 1010 is applied.

Solution:

V

Rb

Rb

Rb

RbVR

Rb

Rb

Rb

RbVRV

reff

reffo

973.210008

)]01()12()04()18[(5470

)]8

1

8

2

8

4

8

8([

)]8

1

4

1

2

11([

0123

0123


Advantages

Simple Construction/Analysis

Fast Conversion

Disadvantages

Requires large range of resistors (2000:1 for 12-bit DAC) with necessary high precision for low resistors

Requires low switch resistances in transistors

Can be expensive. Therefore, usually limited to 8-bit resolution.

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R-2R Ladder

Bit: 0 0 0 0

Each bit corresponds to a switch: If the bit is high, the corresponding switch is connected to the inverting input of the op-amp. If the bit is low, the corresponding switch is connected to ground.

4-Bit Converter

Vout

Vref

Vref V2 V1 V3

R-2R Ladder

Ideal Op-amp

2R 2R

V3

RRR

RRR

22

22eq

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Vref V2 V1 V3

R-2R Ladder

V2 V3

R R

2232

1VV

RR

RV

Likewise,

122

1VV

ref12

1VV

I

IRV out

Vref V2 V1 V3

R-2R Ladder

Results:

ref1ref2ref32

1,

4

1,

8

1VVVVVV

R

Vb

R

Vb

R

Vb

R

VbRV

16842

ref0

ref1

ref2

ref3out

Where b3 corresponds to bit 3, b2 to bit 2, etc. If bit n is set, bn=1 If bit n is clear, bn=0

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R-2R Ladder

16

1

8

1

4

1

2

10123refout bbbbVV

For a 4-Bit R-2R Ladder (R=Rf)

For general n-Bit R-2R Ladder or Binary Weighted Resister DAC

i

n

i

inbVV2

1

1

refout

R-2R Ladder

Advantages

Only two resistor values (R and 2R)

Does not require high precision resistors

Disadvantage

Lower conversion speed than binary weighted DAC

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Example 2 (a)

For the circuit shown above with Vref = 5V and R = Rf = 2kΩ, calculate the output voltage V0 for an input code word 1110.

16

1248 0123 bbbbVV refo

Example 2 (a)

Vref = 5V

R=Rf = 2kΩ

input code word 1110

Vo = -5 [(8x1)+(4x1)+(2x1)+(1x0) /16]

= - 5 * (8 + 4 + 2) / 16

= - 4.375 volts

16

1248 0123 bbbbVV refo

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Example 2 (b)

Find the output voltage for the R-2R DAC shown below. The digital input is 110.

Example 2 (b)

AmAmAI

I

mAk

V

R

VI

mAk

V

R

VI

ref

refin

33.830833.02

1667.0

2

1667.030

5

2

333.015

5

21

2

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Example 2 (b)

VkmARIV

mAmAmAIII

AmAmAI

I

fTo

T

75045.31525003.0

25003.00833.01667.0

66.4104166.02

0833.0

2

12

10

Pros & Cons

Binary Weighted R-2R

Pros Easily understood

Only 2 resistor values

Easier implementation

Easier to manufacture

Faster response time

Cons

Limited to ~ 8 bits

Large number of resistors

Susceptible to noise

Expensive

Greater Error

More confusing analysis

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3. Selection of DAC

For the selection of a DAC, there are several parameters that can determine the suitability of a particular device.

Resolution It is the smallest possible change in the analog output as a result of the change in digital input. Resolution should be as high as possible.

Example 3:

A 4 bit D/A converter have an output range of 0 to 1.5 V. Define its resolution. Solution: Given, n = 4 = number of bits Full scale output, VOFS = 1.5V

Thus the output voltage can have 16 different values including zero. Resolution: Thus, an input change of 1 LSB changes the output by 100 mV.

LSBmVV

Rn

OFS/100

15

5.1

116

5.1

12

1622 4 n

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Output Voltage Range This is the difference between the maximum and minimum output voltages expressed in volts.

Example 4: Calculate the output voltage range of a 4-bit DAC if the output voltage is +4.5V for an input of 0000 and +7.5V for an input of 1111. Solution: Output voltage range = 7.5 – 4.5 = 3.0V


Accuracy It indicates how close the analog output is to its theoretical value. It is the deviation of actual output from the theoretical value. Linearity The relation between the digital input and analog output should be linear.

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Settling time The time taken for the applied digital input to be converted to an analog output. Typical period can be as low as 100ns, making DA conversion a very fast process compared with those of AD conversion.

Input coding The digital input can be in binary format or it can be in binary coded decimal format depending on the application. Binary format is more commonly used.


Binary-coded decimal, or BCD, is a method of using binary digits to represent the decimal digits 0 through 9. A decimal digit is represented by four binary digits, as shown below:

BCD Decimal 0000 0

0001 1 0010 2

0011 3

0100 4

0101 5

0110 6

0111 7 1000 8

1001 9

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It should be noted in the table above that the BCD coding is the binary equivalent of the decimal digit. However, BCD and binary are not the same. For example,

4910 in binary is 1100012, but

4910 in BCD is 01001001BCD. Each decimal digit is converted to its binary equivalent.

Analog to Digital Data Conversion

2. ADC

Many types of ADC

Digital-Ramp ADC

Successive Approximation ADC

Flash ADC

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Digital-Ramp ADC

Conversion from analog to digital form inherently involves comparator action where the value of the analog voltage at some point in time is compared with some standard point.

A common way to do that is to apply the analog voltage to one terminal of a comparator and trigger a binary counter which drives a DAC.

Digital-Ramp ADC

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Digital-Ramp ADC

The output of the DAC is applied to the other terminal of the comparator.

Since the output of the DAC is increasing with the counter, it will trigger the comparator at some point when its voltage exceeds the analog input.

The transition of the comparator stops the binary counter, which at that point holds the digital value corresponding to the analog voltage.

Successive approximation ADC

Illustration of 4-bit SAC with 1 volt step size

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Successive approximation ADC

Much faster than the digital ramp ADC because it uses digital logic to converge on the value closest to the input voltage.

A comparator and a DAC are used in the process.

Flash ADC

It is the fastest type of ADC available, but requires a comparator for each value of output.

(63 for 6-bit, 255 for 8-bit, etc.)

Such ADCs are available in IC form up to 8-bit and 10-bit flash ADCs (1023 comparators) are planned.

The encoder logic executes a truth table to convert the ladder of inputs to the binary number output.

Illustrated is a 3-bit flash ADC with resolution 1 volt

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Flash ADC

The resistor net and comparators provide an input to the combinational logic circuit, so the conversion time is just the propagation delay through the network - it is not limited by the clock rate or some convergence sequence.


T y p e o f A D C S p eed P r ice N o ise

Im m u n ity

C o n v ersio n

T im e

V o lta g e to

freq u en cy

C o n stan t

D u a l s lo p e V ary

S ta irca se

ra m p

V ary

fT

n2max

S u ccess iv e

a p p ro x im a tio n

C o n stan t

f

nT

P a ra lle l (o r

fla sh )

N o t feas ib le

fo r h igh

reso lu tio n

C o n stan t

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4. Selection of ADC

The parameters used in selecting an ADC are very similar to those considered for a DAC selection.

• Error/Accuracy: Quantizing error represents the difference between an actual analog value and its digital representation. Ideally, the quantizing error should not be greater than ± ½ LSB.

• Resolution: DV to cause 1 bit change in output • Output Voltage Range Input Voltage Range • Output Settling Time Conversion Time • Output Coding (usually binary)


To measure an AC voltage at a particular instant in time, it is necessary to sample the waveform with a ‘sample and hold’ (S/H) circuit.

Hold

Sample

Input Output to

ADC

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5. Worked Examples

If the clock rate is 2MHz, calculate the maximum conversion time of

(a) a 8-bit staircase ramp ADC.

(b) a successive approximation ADC.

Solution:

(a) For a 8-bit staircase ramp ADC, the maximum number of count is

nc = 28 = 256

Therefore, the maximum conversion time is

ssf

nT c

c 12810128102

256 6

6


(b) For a 8-bit successive approximation ADC, the conversion time is constant and equal to

ssf

nTc 4104

102

8 6

6

It can be noted that the conversion speed of successive approximation ADC is much faster than the staircase ramp type.

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Frequency to Voltage Converter & Voltage to Frequency Converter

Where an instrumentation system is based mainly on capturing voltage signals (analogue multiplexer and A/D) it may be inconvenient to provide separate inputs for pulse or frequency signals. They can be converted to a voltage by a Frequency to Voltage converter circuit, F/V.

(Conversely some systems are designed to capture pluses or frequencies for them voltages can be converted to frequencies, V/F. The integrated circuits used are often the same.)

Frequency to Voltage converter

The LM331 is a V/F used here as F/V. A pulse train or square wave of at least 3v amplitude. 10kHz produces an output of 10v the linearity is good. However, the circuit has a slow response to input changes

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Frequency to Voltage converter

The operating principle here can be applied to any monostable circuit. The zero crossings of the pulse of frequency signal are used to trigger the monostable, whose fixed width pulses are integrated by the RC filter to produce a dc voltage. The higher the frequency the higher the voltage. A simple circuit like this will need calibration.

Voltage to Frequency Converter

In some circumstances sending a analogue signal into a measurement system is not the best solution to a problem, there may be excessive noise or a long distance between sensor and system or simply all the other signals may be digital. One solution is to convert the analogue voltage to a frequency.

It is possible to use Op Amps or other common ICs (e.g. 555 Timer) but a better performance comes from specialist ICs.

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The LM331again, this time

as F/V, it offers a highly linear conversion, 0.01% max and wide frequency range, 1to 100kHz in a single simple to use package.

The output is a digital pulse train that is easily interfaced to digital measurement systems.


Typical applications are as shown.

The output of a single sensor (photo-transistor, temperature sensor) is converted to a frequency for transmission to a measurement system.

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The internal circuitry is complex and difficult to emulate using simpler devices.

Other V/F:F/V integrated circuit are AD650 and LM2907

Thank you for coming

• .

konversi data analog ke digital - dina maizana

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