Patent ID: 8866542

Claim:
A low frequency filter, comprising: a non-integrating operational amplifier circuit having an input and an output; a two-integrator loop filter circuit having a first operational amplifier integrator and a second operational amplifier (Op-Amp) integrator fed by the first operational amplifier integrator, the non-integrating operational amplifier circuit feeding the first integrator, the second Op-Amp integrator having an output feeding the input of the non-integrating operational amplifier in a loop path, thereby forming a second-order low pass filter; the first and second integrators each having an inverting input and a non-inverting input; and a first pair of resistors R 1 and R 2 and a second pair of resistors R 3 and R 4 , R 1 and R 2 having a common terminal connected to the non-inverting input of the first Op-Amp integrator and R 3 and R 4 having a common terminal connected to the non-inverting input of the second Op-Amp integrator, R 1 being connected to the output of the non-integrating operational amplifier, R 3 being connected to the output of the first operational amplifier integrator, and R 4 being connected in a feedback path to the input of the non-integrating operational amplifier.