Signal Conditioningmohammad iqbal� iqbal.umk@gmail.com

Teknik Elektro

Universitas Muria Kudus

2

Signal Conditioning

1. Introduction to signal conditioning

2. Bridge circuits

3. Amplifiers

4. Filters

3

Amplifiers

4

Op amp characteristic

5

Summing amplifier

+−= 2

3

21

1

2 VR

RV

R

RVout

6

Noninverting amplifier

inout

outinin

VR

RV

R

VV

R

V

II

+=

=−+

=+

1

2

21

21

1

0

0

7

Exercise 7

Design a high impedance

amplifier with a voltage

gain of 42 if R1 = 1 kΩ is

chosen.

8

Differential amplifier

( )CMRRCMRA

ACMRR

VVV

cm

bacm

10log20

2

=

=

+=

( )baout VVAV −=• The transfer function;

• Common mode rejection;

( )121

2 VVR

RVout −=

9

Voltage-to-Current converter

( )

( )

543

354

42531

31

2

RRR

RI

VRR

R

RRRRR

VRR

RI

m

sat

ml

in

++

−+

=

=+

−=

10

Current-to-Voltage converter

IRVout −=

11

Integrator

tRC

KV

dtVRC

V

dt

dVC

R

V

out

inout

outin

−=

−=

=+

∫1

0

12

Exercise 8

Use an integrator to

produce a linear ramp

voltage rising at 10 V per

ms. Determine the R and C.

13

Differentiator

dt

dVRCV

R

V

dt

dVC

inout

outin

−=

=+ 0

14

Linearization

( )

=

=+

R

VGV

VIR

V

inout

outin 0

15

Linearization

( ) ( )

( ) ( )RIVV

VIVI

eincout

outout

0

0

log1

log1

exp

αα

α

−=

=

16

Filters

17

Filters

• Filter : a circuit that is designed to pass signals with desired frequencies and reject or attenuate others

• 4 types of filters:

1. Low-pass filter: passes low frequencies and stops high frequencies

2. High-pass filter: passes high frequencies and rejects low frequencies

3. Band-pass filter: passes frequencies within a frequency band and blocks or attenuates frequencies outside the band

4. Band-reject filter: passes frequencies outside a frequency band and blocks or attenuates frequencies within the band

18

Low-pass RC filter

19

Low-pass RC filter

• Critical frequency:

• Output-to-input voltage ratio:

RCfc π2

1=

( )2/11

cin

out

ffV

V

+=

20

Exercise 9

A measurement signal has a frequency less than

1 kHz, but there is unwanted noise at about 1

MHz. Design a lowpass filter that attenuates the

noise to 1% if a capacitor 0.01 µF has been

used. What is the effect on the measurement

signal at its maximum of 1 kHz?

21

High-pass RC filter

22

High-pass RC filter

• Critical frequency:

• Output-to-input voltage ratio:

RCfc π2

1=

( )( )2/1/

c

c

in

out

ff

ff

V

V

+=

23

Exercise 10

Pulses for a stepping motor are

being transmitted at 2000 Hz.

Design a highpass filter to reduce

60 Hz noise and reduce the pulses

by no more than 3 dB.

24

Design Methods

1. Determine critical frequency, fc

2. Select standard capacitor (µF – pF)

3. Calculate required resistance (1 kΩ - 1 MΩ)

4. Use nearest resistance standard value to

calculated value

5. Consider tolerance in resistors and capacitors

25

Practical considerations

1. Very small resistance -> lead to large currents and

loading effects -> avoid large capacitance

(R= kΩ -MΩ, C= µF – pF)

2. The exact fc is not important, choose R and C of

approximately to the fc

3. Isolation filter input/output with voltage follower

4. Cascade RC filters to improved fc sharpness ->

consider loading

26

Band-pass RC filter

27

Band-pass RC filter

• Critical frequency:

• Output-to-input voltage ratio:

HHL CR

fπ2

1=

( ) ( )[ ]

L

H

HLLH

H

in

out

R

Rr

ffrffff

ff

V

V

=

+++−=

2222 1

LLH CR

fπ2

1=

28

Exercise 11

A signal conditioning system uses a frequency

variation from 6 kHz to 60 kHz to carry

measurement information. There is considerable

noise at 120 Hz and at 1 MHz. Design a

bandpass filter to reduce the noise by 90%.

What is the effect on the desired passband

frequencies if r = 0.01? Determine all the

resistors and capacitors.

29

Band-pass RC filter

30

Band-reject RC filter

31

Twin-T notch filter

32

Twin-T notch filter

• Critical frequency:

• Grounding resistor and capacitor:

cn ff 785.0= RCfC π2

1=

cH ff 57.4=cL ff 187.0=

101R

Rπ=

πC

C10

1 =