**Active Filters**

In general, the following graphics are taken from Electronics Tutorials and from Circuits Today.

**First Order Low Pass Filter**

**Second Order Low Pass Filter**

**Filter Phase Shift (Bode Plot)**

**Roll-off by order of filter**

**First Order High-Pass Filter**

**Second Order High-Pass Filter**

**Simple Band Pass Filter**

**Band Pass Filter Response**

**Inverting Band Pass Filter**

**Narrow Infinite Gain Multiple Narrow**

**Band**

**Pass Filter**

**Narrow Band Pass Filter Response**

**Wide Band Stop Filter (Band Reject Filter)**

**All Pass Filter**

Wikipedia states this "is a signal processing filter that passes all frequencies equally in gain, but changes the phase relationship between various frequencies. It does this by varying its phase shift as a function of frequency. Generally, the filter is described by the frequency at which the phase shift crosses 90° (i.e., when the input and output signals go into quadrature – when there is a quarter wavelength of delay between them).

They are generally used to compensate for other undesired phase shifts that arise in the system, or for mixing with an unshifted version of the original to implement a notch comb filter.

They may also be used to convert a mixed phase filter into a minimum phase filter with an equivalent magnitude response or an unstable filter into a stable filter with an equivalent magnitude response.