K305(2004) 查看數據表（PDF） - STMicroelectronics

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K305
(Rev.:2004)

550 MHz, Low Noise Current Feedback Amplifier

STMicroelectronics 

Active Filtering

8 Active Filtering

Figure 35: Low-pass active filtering, Sallen-Key

C1

R1

IN

R2

+

C2

_

Rfb

RG

OUT

100Ω

TSH350

From the resistors Rfb and RG we can directly calculate the gain of the filter in a classical non-inverting

amplification configuration:

AV = g = 1 + R--R---f-g-b--

We assume the following expression as the response of the system:

Tjω = V---V--o--i--un---j-t-ωj--ω--- = 1-----+-----2----ζ----ω-j----ω--g--c-----+-------(--ω--j----ω---c-----)--2---2----

The cut-off frequency is not gain-dependent and so becomes:

ωc

=

------------------1-------------------

R1R2C1C2

The damping factor is calculated by the following expression:

ζ = 12-- ωc(C1R1 + C1R2 + C2R1 – C1R1g)

The higher the gain, the more sensitive the damping factor is. When the gain is higher than 1, it is

preferable to use some very stable resistor and capacitor values. In the case of R1=R2=R:

ζ = 2----C-----2-----–----C-----1----R---R------f---g-b-----

2 C1C2

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