Analog Filter Wizard

Problem:
How does a non-expert designer quickly implement an analog filter?

Solution:
This is the Texas Instruments Filter Wizard. The designer is cautioned that there are many factors that can affect analog design, and this wizard covers only the most common options. Those that are offered will probably satisfy the requirements of 90% of applications. Please contact Texas Instruments Applications department if there are any questions or doubts about the design.

Assumptions:

• The designer is utilizing a single power supply rail.
• The designer is not using current feedback opamps.
• The designer is not using fully-differential opamps.

If these assumptions are not correct, the designer should utilize the Filter Design Expert.

If these assumptions are OK, the designer can use this wizard.

This Wizard utilizes single-supply circuits. The designer, if not familiar with the topics, may want to review Coupling Capacitors (Cin in the schematics) and Virtual Grounding (Vcc/2 in the schematics).

The first question a designer must ask is:

• What frequency (or frequency range) needs to be rejected, and what frequency (or frequency range) needs to be passed?

The process of filtering is the process of passing some frequencies and rejecting others. Once the designer knows exactly what frequencies must be passed and which ones must be rejected, then the designer must classify the filter:

1. Do low frequencies need to be passed and high frequencies rejected? The designer needs to implement a Low Pass Filter.
   
   
2. Do high frequencies need to be passed and low frequencies rejected? The designer needs to implement a High Pass Filter.
   
   
3. Does only a single frequency (or narrow frequency range) need to be passed? The designer needs to implement a Bandpass Filter. Otherwise:
   
   
4. Does a wide frequency range need to be passed with rejection above and below the range? The designer should implement a High Pass Filter, cascaded with a Low Pass Filter.
   
   
5. Does only a single frequency (or narrow frequency range) need to be rejected? The designer needs to implement a Notch Filter.
   
   

If this filter design wizard produces a result that is unacceptable, the designer may utilize the Filter Design Expert, which will give many more options.