실험, 06 - 저역통과필터

I. 이론

1. 수동필터 vs 능동필터

ㅇ 저역통과필터

ㅇ 수동필터 vs 능동필터

- 수동 LPF

- 능동 LPF

ㅇ 능동필터의 특징

- Can have gain

- Amplifier: prevents impedance loading of the following stage

Good isolation between stages: hign Zin low Zout

Multiple stages can be combined to tailor the response.

- Inductors are not used: bulky or expensive, especially at audio frequencies

- Filter response tuned with inexpensive R

Tunable over a wide range

- In some active filters, one filter parameter can be adjusted without affecting the others.

- Upper frequencies are limited by the frequency response of the amplifier.

2. 능동 LPF

ㅇ 필터차수

- 필터에 사용된 에너지 저장부품의 개수와 동일

- 차수가 클수록 roll-off 기울기 증가

Roll-off = 20N dB/decade

2.1 1차 LPF

2.2 2차 LPF

ㅇ Multiple feedback topology

- Two poles in the transfer function

ㅇSallen-Key topology

- 특징: 2차 능동필터 구조, VCVS 필터 구조의 일종, 회로단순

- LPF

- HPF

- BPF

ㅇ Biqud filter

-Transfer function: ratio of two quadratic functions

3. 실험회로 해석