I used the suggested design from the filter design tool.
But the simulation in LTspice got abnormal results.
Hey Lin,
Here is an extraction and an improved RC value set using the OPA348 for analysis purposes ( as I do not have the TLV6001 in my MFB design tool right now) this flow has adjusted off perfect gain of 1 slightly to get better Fo =1.5kHz and Q= .707 match, The RC numbering is slightly different, but the schematic shows that.
You are not showing your supply values, if single 5V you are probably clamped against the negative supply causing sim problems, try +/-2.5V supply for sim.
Hi Jerry,
Here is the design data.
I changed the cutoff frequency as 7.5kHz.
The simulation result still abnormal.
The value of Vcc is 5V.
Vee connected to ground.
Hey Lin,
Your issue is the DC bias point.
With an input of 2.5Vdc in the inverting side, the output is trying to force to -2.5V. This can be seen in the below circuit where the supplies are shifted down, and the DC input is shifted down slightly.
Changing your Voff to -2.5 will give you a proper output in the linear range of the amplifier.
Best,
Jerry
The RC values I gave you were coming out of a more recent tool I developed for the online Intersil active filter designer, not the TI tool. The TI solution flows are coming from the old (1987) BurrBrown Filterpro tool. Here are the 7.5kHz cutoff RC values, one of the improvements in my flow is to reduce the noise gain peaking internal to the filter, slightly reduces integrated noise.
Without running a TINA sim on this, here is a LG plot I produce inside my tool to make sure the op amp is adequate BW, for your design I am getting about 37dB min loop gain using the OPA348 GBP - which is really good
As long as I had this open, I can drop in the values you showed out of the TI tool still using the same op amp, not a huge change(about 1dB lower min LG in band) but kind of free dynamic range,
