Patent ID: 6396343
Filing Date: 2002-05-28
Classification: H03F

Abstract:
An amplifier circuit comprising:a first operational amplifier having a non-inverting input, an inverting input, and a differential output e4, said non-inverting input receiving a differential input signal e2; a second operational amplifier having a non-inverting input, an inverting input, and a differential output e3, said non-inverting input receiving a differential input signal e1; a twin T-feedback network including R1, R2, R3, R4, Rp, Cp, where the resistors R2 and R4 form the first â€œTâ€  with the capacitor Cp and the resistor Rp, and where the resistors R1 and R3 form the second â€œTâ€  with the resistor Rp and the capacitor Cp; and a resistor RC and a capacitor Cc connected in series, wherein the resistor R4 is connected to the output e4 of the first operating amplifier, the resistor R3 is connected to the output e3 of the second operating amplifier, the resistors R2 and Rc are connected to the inverting input of the first operating amplifier, and the resistor R1 and the capacitor Cc are connected to the inverting input of the second operating amplifier, and wherein said e2 and e1 is a low frequency, low amplitude differential signal having a relatively high DC offset, and wherein values for R1, R2, R3, R4, Rp, RC, Cc, and Cp are chosen to give said circuit a high gain at the differential outputs e3 and e4 and a cut-off frequency sufficient to remove said DC offset.