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

Bas Basic ic El Elec. ec. En Engr gr. . Lab Lab EC ECS S 204 04/2 /210 Dr. Prapun Suksompong prapun@siit.tu.ac.th Office Hours: BKD 3601-7 Tuesday 9:30-10:30 Friday 14:00-16:00 1

Lab 8  Filter  Passive LPF  Active LPF  Passive HPF  Circuit Design 2

Lab 7.B: Inverting Integrator: + v C - i C C   Z   R C V+ V  V o i   R X i in +   v i V 1    v o + i      - R j C V-  The gain at f = 0 is unbounded. 3

Lab 7.B: Inverting Integrator  In practical circuit, a large resistor R p is usually shunted across the capacitor R p   Z / / R   C p  V V C o i   R R V+   R V    p i   X     i in R j R C 1 + p v i v o + - V-  Observe that at f = 0, the gain is finite. 4

Filter  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”) A Filter  V (j ) V in ( j  ) V out ( j  )   out H(j )  V (j ) in 5

Filter  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 6

Low-pass filter (LPF) R Transfer Function 1  ( ) H j = + j RC  LP passive , 1 v in v out C Cut-off frequency 1 1      2 f  c c RC (a) A passive low-pass filter. C Transfer Function R 2   R 1   2   H ( j ) = R 1  LP active ,   R 1 + j R C 1 2 Cut-off frequency 1 1 v in      v out 2 f  c c R C 2 7 (b) An active low-pass filter

Part A: Passive LPF R Transfer Function 1  H ( j ) = + j RC  LP passive , 1 v in v out C Cut-off frequency 1 1      2 f  c c RC (a) A passive low-pass filter. 8

High-pass filter (HPF) Transfer Function C  j RC  H ( j ) = + j RC  HP passive , 1 v in v out Cut-off frequency R 1 1      2 f  c c RC (a) A passive high-pass filter. R 2 Transfer Function  j R C   2 H ( j ) = C R 1  HP active , 1 + j R C 1 Cut-off frequency v in v out 1 1      2 f  R C 1 (b) An active high-pass filter 9

Part B: Passive HPF Transfer Function C  j RC  H ( j ) = + j RC  HP passive , 1 v in v out Cut-off frequency R 1 1      2 f  c c RC (a) A passive high -pass filter. 10

Part C: Active LPF Design C =______ R 2 =______ V SS =______ R 1 =______ IN OUT v in v out V DD =______ 11

Part D: Bandpass filter (BPF) - Optional High-Pass Filter Low-Pass Filter C 1 R 2 v in v out C 2 R 1 Lower cutoff frequency Upper cutoff frequency (Determined by HP filter) (Determined by LP filter) 1 1 1 1           2 f 2 f   1 1 2 2 R C R C 1 1 1 2 2 2 12