LMF100 switched capacitors filter.
I intend to use it for an f0 =10 Hz thus fCLK to drive the filter (ratio 100:1) should be 10*100 =1000Hz but I have available only 120 Hz. The micro in charge cannot provide 1KHz what would make my life easier.
To use it in Mode 3 as a LPF where I can adjust the fCKLK / f0 ratio via resistors R2 and R4, I calculate:
Asuming R1 =18K and HOLP =1, R4 is also =18K.
To have a relationship 100:1, I calculate R2 as per the equation
fo = fCLK/100 * SQRT (R2/R4), obtaining
R2 = 1250000 ohms for a ratio of 1000/120 =8.33333...
My questions:
a) Is it actually appropriate to use R1 =18K? How to find out that?
b) R2 seems to be quite high (!) Is it convenient for this kind of circuit?
c) To make R2 smaller I should make R1 also smaller. Is that convenient as well? If yes, how much less?
Datasheet here:
https://www.google.com.ar/url?sa=t&rct=j&q=lmf100%20datasheet&source=web&cd=1&ved=0CCMQFjAA&url=http%3A%2F%2Fwww.swarthmore.edu%2FNatSci%2Fecheeve1%2FRef%2FDataSheet%2FLMF100.pdf&ei=oumqTojPCcLq0gGXt7GGDw&usg=AFQjCNGEdtviaBKR6vBPoKNYZc9PBKlkng
Help appreciated.
I intend to use it for an f0 =10 Hz thus fCLK to drive the filter (ratio 100:1) should be 10*100 =1000Hz but I have available only 120 Hz. The micro in charge cannot provide 1KHz what would make my life easier.
To use it in Mode 3 as a LPF where I can adjust the fCKLK / f0 ratio via resistors R2 and R4, I calculate:
Asuming R1 =18K and HOLP =1, R4 is also =18K.
To have a relationship 100:1, I calculate R2 as per the equation
fo = fCLK/100 * SQRT (R2/R4), obtaining
R2 = 1250000 ohms for a ratio of 1000/120 =8.33333...
My questions:
a) Is it actually appropriate to use R1 =18K? How to find out that?
b) R2 seems to be quite high (!) Is it convenient for this kind of circuit?
c) To make R2 smaller I should make R1 also smaller. Is that convenient as well? If yes, how much less?
Datasheet here:
https://www.google.com.ar/url?sa=t&rct=j&q=lmf100%20datasheet&source=web&cd=1&ved=0CCMQFjAA&url=http%3A%2F%2Fwww.swarthmore.edu%2FNatSci%2Fecheeve1%2FRef%2FDataSheet%2FLMF100.pdf&ei=oumqTojPCcLq0gGXt7GGDw&usg=AFQjCNGEdtviaBKR6vBPoKNYZc9PBKlkng
Help appreciated.