Decibel | Dokumen 471 DECIBEL

(1)

Pengertian Gain, Attenuasi dan

Decibels

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(2)

Gain, attenuation, dan

Decibel

•

Gain = penguatan, atau dikatakan

sebagai perbandingan output dan input

dimana

output lebih besar daripada input

.

•

Attenuation = redaman, dikatakan

sebagai perbandingan output dan input

dimana

output lebih kecil daripada input.

(3)

Gain = amplification

in out v

V

input

output

A



in out p

P

input

output

A



in out

(4)

Contoh soal

000

.

25

10

30

10

750

6 3







_



in out v

V

A

mW

W

P

A

P

therefore

P

A

in

p out in

in out p

75

075

.

0

80

6



1. Berapa penguatan tegangan sebuah penguat yang menghasilkan

tegangan keluaran 750 mV dari sumber masukan 30



V ?

(5)

Contoh soal

W

P

A

P

therefore

P

A

out in p out in out p p

8

.

6

)

10

40

(

170

17

2

5

3 3 2 1

















20

3

/

60

3

60

,

3

60

10

25

10

5

.

1

2 2 1 2 1 6 3















_ 

A

and

A

then

A

if

A

P

A

p in out p

3. Three cascaded amplifiers have power gain of 5, 2, and 17.

The input power is 40 mW. What is the output power?

4. A two stage amplifier has an input power of 25



W and an output

(6)

Attenuation = redaman













2 1

2

R

V

_out _in

in out

V

input

output

A

n

attenuatio



V_in

R₁=200

R₂=100

0

.

3333

300

100

2 1

2















R

A

Loss stage

Loss circuit

Loss component

V_in _V

out

A₁=0,2 A₂=0,9 A₃=0,06

A_T= A₁ x A₂ x A₃ = 0.2 X 0.9 x 0.06 = 0.0108

(7)

Redaman

25

,

0

1000

250

1

)

4

(

25

,

0

)

250

750

(

250

1

2 1 1







A

_T

V_in

R₁=750

R₂=250

A₂= 4

V_out = V_in

Loss stage

V_in = 1.5 V 0.15V 1.5V 0.45V Vout = 6.75 V

A₁= 0.1 A₂= 10 A₃= 0.3 A4= 15

(8)

Contoh soal

045

.

0

470

,

10

470

1 2

1







A

R

A

3

.

22

045

.

0

1

045

.

0

1



A

₂

A

₂



A voltage divider like that shown in Fig. 2-5 has values of R1 = 10 k and

R2 = 470 .

a. What is the attenuation?

b. What amplifier gain would you need to offset the loss for an overall gain of 1 ?

A_T = A₁A₂

where A₁ is attenuation and A₂ is the amplifier gain

Note:

(9)

Contoh soal

An amplifier has a gain of 45,000, which is too

much for the application. With an input voltage of

20



V, what attenuation factor is needed to keep

the output voltage from exceeding 100 mV?

Let

A1

= amplifier gain = 45,000;

A2

=

attenuation factor;

AT

= total gain.

1111

.

0

000

,

45

000

,

5

000

,

5

10

20

10

100

1 2

2 1

6 3







_



A

therefore

A

V

A

T T

(10)

Decibel (dB)

)

3

(

log

10

)

2

(

log

20

)

1

(

log

20

in out

P

dB

I

dB

V

dB



Formula (1) untuk menyatakan penguatan (gain) atau

redaman (attenuation)

tegangan

dari suatu rangkaian.

Formula (2) untuk penguatan atau redaman

arus

Formula (3) untuk penguatan atau redaman

daya

It is common for electronic circuits and systems to have extremely high gains or attenuations, often in excess of 1 million.

Dengan mengubah angka di atas menjadi decibel (dB) akan

(11)

Contoh

4

.

64

)

22

.

3

(

20

67

.

1666

log

20

003

.

0

5

log

20



dB



0

.

04



10

(

1

.

398

)

13

.

98

log

10

50

2

log

10















dB

a. An amplifier has an input of 3 mV and an output of 5 V. What is

the gain in decibels?

b. A filter has a power input of 50 mW and an output of 2 mW.

What is the gain or attenuation?

(12)

dB (decibel)

Adalah satuan factor penguatan jika nilainya positif, dan

pelemahan/redaman/loss jika nilainya negative.

Jika input = 1 watt, output = 100 watt maka terjadi

penguatan (G) 100 kali, maka G = 10 log 100/1 = 20 dB

Jika input = 100 watt, output = 50 watt maka terjadi

redaman/loss daya (G), maka G = 10 log 50/100 = -3 dB

(13)

•

dBW (Decibel Watt ) dan dBm

adalah satuan level

daya

•

dBW :

adalah satuan level daya dengan

referensi daya 1 watt

P(dBW) = 10 Log P(watt)/1

watt

dBm:

adalah satuan level daya dengan referensi

daya 1 mW = 10-3 watt

•

P (dBm) = 10 Log P(watt)/10-3 watt

•

10 Watt = P (dBW) = 10 Log 10 Watt/1 Watt (= 10 Log

10 = 10 dBW)

•

1000 Watt = P (dBW) = 10 Log 1000 Watt /1 Watt (=

10 Log 1000 = 30 dBW)

•

10 Watt = P(dBm) = 10 Log 10/10-3 = 10 Log 104 =

10*4 = 40 dBm

•

100 Watt = P(dBm) = 10 Log 100/10-3 = 10 Log 105

= 10*5 = 50 dBm

•

1000 Watt = P(dBm) = 10 Log 1000/10-3 = 10 Log

(14)

• Terlihat bahwa dari dBw ke dBm terdapat selisih 30 dB

sehingga dapat dirumuskan :

P (dBm) = P (dBW) + 30 atau, P (dBW) = P (dBm) – 30

Contoh :

1. Sebuah Amplifier mempunyai gain = 20 dB, jika

diberi input 10 dBm berapa output amplifier

tersebut? Jawab :

Pout (dBm) = Pin(dBm) + G =

10 + 20 = 30 dBm.

2.

Sebuah Amplifier dengan gain 30 dB, jika

outputnya sebesar 45 dBm berapa level

inputnya? Jawab :

Pout(dBm) = Pin (dBm) + G =?

Pin = Pout G = 45 - 30 = 15 dBm

3.

Output amplifier sebesar 30 dBm akan dilewatkan

kabel dengan redaman / loss 2 dB. Berapa level

sinyal setelah melewati kabel?

(15)

Loss stage

A₁=15dB A₂= - 20dB A₃= 35dB

A

_T

= A

₁

+ A

₂

+ A

₃

A

_T

= 15 – 20 + 35 = 30 dB

gain

(

redaman

)

total:

(16)

Contoh soal

1. A power amplifier with a 40 dB gain has an output power of 100 W. What is the input power?

2. A power amplifier has a gain of 60 dB. If the input voltage is 50V,

what is the output voltage?

mW

P

anti

P

dB

P

dB

out in in out in out in out in out in out

10

000

,

10

100

000

,

10

4

log

10

40

log

10

log

10

4





(17)

dBm

dan

dB



dBm adalah ratio logaritmik dengan acuan 1 mW



untuk daya

dB



adalah ratio logaritmik dengan acuan 1



Volt



untuk

tegangan

V

dB

dan

mW

P

dBm

x x



1

log

20

1

log

10



Contoh:

1. Nyatakan 20 dBm dalam watt.

2. Nyatakan 40 dB dalam volt.

Daya = 100 mW

Tegangan = 100 V

Loss stage

A₁= 30dB A₂= - 10dB A₃= 3dB

1mW ???