Need programmable cutoff LP filter

[Amanda Robin]

Hi all,

Does anyone have a recommendation for a digitally programmed low-pass
filter like Maxim's 270/271 except with a lower range for the cutoff
frequency?

I need an adjustable cutoff from about 200 - 2000 Hz (the 270's range is
1 - 25 kHz). I would prefer not to use a programmable filter that uses
resistors or pots because I need high precision. I'll have at least 5 of
these, and the cutoff frequencies have to match to +- 2 Hz or so (audio
application).

My other option I guess is to get filters for which you adjust the
cutoff with an external clock, have one clock serve all, and adjust the
clock frequency.

But I'd sure like to know about any easily programmable low-pass filter
chips.

Thanks in advance,
Amanda

 

[Rene Tschaggelar]

Hi all,

Does anyone have a recommendation for a digitally programmed low-pass
filter like Maxim's 270/271 except with a lower range for the cutoff
frequency?

I need an adjustable cutoff from about 200 - 2000 Hz (the 270's range is
1 - 25 kHz). I would prefer not to use a programmable filter that uses
resistors or pots because I need high precision. I'll have at least 5 of
these, and the cutoff frequencies have to match to +- 2 Hz or so (audio
application).

My other option I guess is to get filters for which you adjust the
cutoff with an external clock, have one clock serve all, and adjust the
clock frequency.

But I'd sure like to know about any easily programmable low-pass filter
chips.

2Hz accuracy ... The concept of filter slope
and dB is known ? What order should these
filters have ?

Rene

 

[Ken Smith]

Hi all,

Does anyone have a recommendation for a digitally programmed low-pass
filter like Maxim's 270/271 except with a lower range for the cutoff
frequency?

I need an adjustable cutoff from about 200 - 2000 Hz (the 270's range is
1 - 25 kHz). I would prefer not to use a programmable filter that uses
resistors or pots because I need high precision. I'll have at least 5 of
these, and the cutoff frequencies have to match to +- 2 Hz or so (audio
application).

2Hz/2000Hz = 0.1%

You really need to go digital with this if you don't want a lot of
trimming to be needed.

Since you are making a low pass, going digital can work quite nicely.
ADCs and DACs that do 24 bits for the audio band are getting common. You
don't really needs one that good however. You can follow the DAC with a
fixed low pass filter at, lets say, 5KHz.