Something about Active Filters

[Crowbar]

I've decided to use an active filter in my scheme. An active filter must be frequency variable(no matter what kind of filter we use: Unity Gain Sallen-Key or Unity Gain State Variable). So there are some idеas(we whant to have some kind of variable resistor): to use Digitally controled potentiometer(such as X9C104), to use AD532 or to use CA3080(I won't use resistor arrays with switches because it's a stone age ). Of course the better linearability the better the tuning. What do you think?

[Bojidar]

Right choice !!!

Hi Crowbar,

That is a right choice!For design filter I use Filterlab (that is free software from Microchip).I will use DS1267 dual pot for GEB and DISK.I don't like to control pot's via I2C.Active filter have better perfomance,and you can change freq. in some time Good Luck

[Crowbar]

Good software. I'm using Don Lancaster's Active filter cookbook, and let me to recommend this book

[porkluvr]

FilterPro

Another very good, quick-and-dirty filter design program is available from Texas Instruments. FilterPro is good for custom Sallen-Key and MFB filter design. It even gives a readout of recommended amplifier bandwidth - very welcome when designing filters with gain. http://focus.ti.com/docs/toolsw/fold...filterpro.html

If you need a good low power amplifier, take a look at Analog Devices OP162 . Although no one spec is exceptional, the whole package looks very nice. Available at Digikey, but SO-8 only, and no duals (OP2162) yet. Lets hope that changes!
http://www.analog.com/en/prod/0%2C28...P162%2C00.html