US 6,396,343 B2Granted

Low-frequency, high-gain amplifier with high DC-offset voltage tolerance

AssigneeNgee Ann Polytechnic

InventorJohnny Chee

Life of this patent

Estimating the term…

Loading patent…

Abstract

The instrumentation amplifier circuit of the present invention is particularly suited for amplifying ECG signals, rejecting common mode signals and removing a DC offset. The preferred embodiment of the present invention basically comprises a front-stage differential amplifier, and a common-mode rejection circuit. By employing a twin-T network, the front stage differential amplifier is able to simultaneously remove the DC offset and achieve high gain using standard off-the-shelf components. The common mode differential gain, however, is zero, which is the desired result. The common-mode rejection circuit removes the common-mode signal to yield only the amplified ECG signal. The present amplifier circuit has a much greater DC offset tolerance than the prior art amplifier while the Common Mode Rejection Ratio (CMRR), residual noise at the output, and the input dynamic range is comparable to that of the prior art amplifier. Moreover, it requires fewer operational amplifiers.

Claims12

Dependent claims

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 “T” with the capacitor Cp and the resistor Rp, and where the resistors R1 and R3 form the second “T” 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.

5 more elements

Dependencies are inferred from the claim text.