Bas Basic ic El Elec. ec. En Engr gr. . Lab Lab EC ECS S - - PowerPoint PPT Presentation

• Dr. Prapun Suksompong

prapun@siit.tu.ac.th

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Bas Basic ic El Elec.

• ec. En

Engr gr. . Lab Lab

EC ECS S 204 04/2 /210

Office Hours: BKD 3601-7 Tuesday 9:30-10:30 Friday 14:00-16:00

Lab 8

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 Filter

 Passive LPF  Active LPF  Passive HPF

 Circuit Design

Lab 7.B: Inverting Integrator:

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 The gain at f = 0 is unbounded.

R + + vo

• iC

iin vi V+ V- X C + vC -

1

C

• i

i

Z V V R V R j C                 

Lab 7.B: Inverting Integrator

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 In practical circuit, a large resistor Rp is usually shunted

across the capacitor

 Observe that at f = 0, the gain is finite.

R + C + vo

• iin

vi V+ V- X Rp

/ / 1

C p

• i

p i p

Z R V V R R V R j R C                  

Filter

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 Used in circuits to

 remove unwanted frequency components, or  enhance wanted ones, or  both

 Transfer function

 Magnitude response ( “voltage gain” or “frequency response”)  phase response (“phase shift”) Vin(j)

) (j ) (j ) H(j

in

• ut

V V

   

A Filter

Vout(j)

Filter

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 By Function:

 Low-pass filter (LPF)  High-pass filter (HPF)  Bandpass filter (BPF)

 By Electronic Realization:

 Active

 contain amplifying devices such as transistors and amplifiers

 Passive

Low-pass filter (LPF)

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R C vout vin

Transfer Function

,

1 ( ) 1

LP passive

H j = + j RC  

Cut-off frequency

c c

f RC    2 1 1   

(a) A passive low-pass filter.

vin R1 vout R2 C

Transfer Function

2 , 1 2

1 ( ) 1

LP active

R H j = R + j R C         

Cut-off frequency

2

1 1 2

c c

f R C      

(b) An active low-pass filter

Part A: Passive LPF

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R C vout vin

Transfer Function

,

1 ( ) 1

LP passive

H j = + j RC  

Cut-off frequency

c c

f RC    2 1 1   

(a) A passive low-pass filter.

High-pass filter (HPF)

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R C vout vin

Transfer Function

,

( ) 1

HP passive

j RC H j = + j RC   

Cut-off frequency

c c

f RC    2 1 1   

(a) A passive high-pass filter.

R1 vout R2 C vin

Transfer Function

2 , 1

( ) 1

HP active

j R C H j = + j R C     Cut-off frequency

1

1 1 2 f R C      

(b) An active high-pass filter

Part B: Passive HPF

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R C vout vin

Transfer Function

,

( ) 1

HP passive

j RC H j = + j RC   

Cut-off frequency

c c

f RC    2 1 1   

(a) A passive high -pass filter.

Part C: Active LPF Design

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R1=______ vout R2 =______ C =______ VSS =______ VDD =______

IN OUT

vin

Part D: Bandpass filter (BPF) - Optional

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vout vin R1 C1 C2 R2

High-Pass Filter Low-Pass Filter

Lower cutoff frequency (Determined by HP filter)

1 1 1 1 1

2 1 1 f C R      

Upper cutoff frequency (Determined by LP filter)

2 2 2 2 2

2 1 1 f C R      