Why you put resistors 62k||68k instead of 240k||100k which are the feedback resistors ?
* MFB-BP.asc
R1 N002 N001 32.43k
R2 N001 0 150
V1 N002 0 AC 0
C1 N001 N003 1n
C2 N001 Out 1n
R3 Out N003 70.58k
E1 Out 0 N004 N003 1e5
V2 N004 0 AC 1
.ac dec 2000 35e3 75e3
.end
To illustrate a previous comment about the role of filter topologies, I see that a Sallen Key biquad with similar Q (≈10) and also equal cap dimensioning has a noise gain around 60, 1/4 of the MFB variant. Besides better noise performance, the OP GBW requirements are reduced by the same factor.
I understand, that the topology doesn't fit your virtual ground design that well.
Two comments on the FilterPro design:I simulate with filter-pro (TI Software) and receive that the last stage (#4) need Min of GBW of 136.97MHz, this value is the same for MFB and SK !
The parameters of the filter: Fc=50KHz, BW=5KHz, Ripple=1dB
Activating both sources doesn't serve a purpose. With V2 of 1V, you are determining noise gain.I simulate according your data and receive G of 234, If V1 is disable or enble with voltage of 1V there is no effect on G=234, the calculation of the gain done with V2.
Activating both sources doesn't serve a purpose. With V2 of 1V, you are determining noise gain.
About which circuit are you talking?
The FilterPro design also has about factor 4 noise gain difference between MFB and SK. But they don't consider it in the specified "GBW requirement", apparently because they use a simplified criterion.
Hi TXRX,
just one reminder: In case noise is a critical issue, you also could consider some filter topologies other than the cascade approach (active realization of a passive ladder structure or PRB approach)
There's no exact minimum. The Q enhancement due to finite GBW can be determined analytically, you can also adjust the filter parameters according to real OP properties. Some commercial filter tools like Nuhertz Filter Solutions have the option.Do you have any idea how to calculate the minimum GBW or other software that you are familiar.
Hi LvM,
Thanks, I simulate and check your design of GIC.
What is the name of the Filter-free software ?
If we define noise gain = |1/β| (inverse feedback factor) it doesn't depend on GBW respectively available loop gain. The actual noise gain will be sligthly reduced (as well as signal gain) if the available loop gain at the frequency of interest is low.Is the Noise Gain depend on GBW parameter ?