problem with filter
Posted: Tue May 05, 2009 7:00 am
Hello Lubin,
When I put an analog signal on the Ao port of the 30f4013 and I connect an oscilloscope on a low pass filter after the OC pins, everything is working correct. (the frequency on the output is exact the same as the input). See the model in the attachment.
At least, with a filter from the expolorer16 model. This filter is working very well.
But when I design a filter with the FDatool (I tried a lot of designs) the system is not working. (So far as I know I can’t design with the FDatool a filter in the way of a discrete transfer Fcn).
I use a very simple function generator (XR2206, home made) which I have connected to an anti-alias filter (made from opamps, 5poles, Low Pass). Cut off frequency of this filter: 600Hz= {(Fs = 1200)/2}
I have connected a Schmitt trigger (74HC14) to this analog filter. The output from this 74HC14 is connected with the Ao port of the 30f4013.
I have connected the OC1 pin of the 30f4013 with a low pass filter (5 poles) of 200Hz.
Xr2206 – Low Pass filter 600Hz – 74HC14 – 30f4013 – Low Pass filter 200Hz
As I mentioned in the beginning: when I connect the output from this last filter with an oscilloscope, the frequency is exact the same as the input form the analog function generator (XR2206). The discrete transfer Fcn filter is working very well. But any other filter designed with the FDatool is, till now, not working.
Casparus
When I put an analog signal on the Ao port of the 30f4013 and I connect an oscilloscope on a low pass filter after the OC pins, everything is working correct. (the frequency on the output is exact the same as the input). See the model in the attachment.
At least, with a filter from the expolorer16 model. This filter is working very well.
But when I design a filter with the FDatool (I tried a lot of designs) the system is not working. (So far as I know I can’t design with the FDatool a filter in the way of a discrete transfer Fcn).
I use a very simple function generator (XR2206, home made) which I have connected to an anti-alias filter (made from opamps, 5poles, Low Pass). Cut off frequency of this filter: 600Hz= {(Fs = 1200)/2}
I have connected a Schmitt trigger (74HC14) to this analog filter. The output from this 74HC14 is connected with the Ao port of the 30f4013.
I have connected the OC1 pin of the 30f4013 with a low pass filter (5 poles) of 200Hz.
Xr2206 – Low Pass filter 600Hz – 74HC14 – 30f4013 – Low Pass filter 200Hz
As I mentioned in the beginning: when I connect the output from this last filter with an oscilloscope, the frequency is exact the same as the input form the analog function generator (XR2206). The discrete transfer Fcn filter is working very well. But any other filter designed with the FDatool is, till now, not working.
Casparus