Signal Common Mode Cancellation For Handheld Low Voltage Testing Device
An apparatus for monitoring bioelectric signals of a patient which includes a processing system and an interface for receiving external electrical signals representative of a condition of the patient. The interface is configured to convey a representation of the received external signals to the processing system, and includes a common mode cancellation amplifier circuit which is adapted to reduce common mode signal noise present in the external signals.
1 . Apparatus for monitoring bioelectric signals of a patient, comprising:
a processing system;
an interface coupled to said processing system for receiving external electrical signals representative of a condition of the patient and for conveying a representation of said received external signals to said processing system, said interface including a common mode cancellation amplifier circuit configured to reduce common mode signal noise present in said external signals, and at least one amplifier circuit configured to alter an amplitude of said external signals; and
wherein said processing system is configured for processing representations of said received external signals with at least one software algorithm to generate at least one index value representative of a patient condition.
2 . The apparatus of claim 1 wherein said interface includes a first stage gain amplifier for amplifying a received electrical signal, said first stage gain amplifier operatively coupled to a gain setting network; and
wherein said gain setting network is a resistor network configured to provide a gain setting for said first stage gain amplifier and to provide a common-mode signal to said common mode cancellation amplifier circuit.
3 . The apparatus of claim 2 wherein said interface further includes an input radio-frequency interference filter circuit coupled between a source of said received external electrical signals and said first stage gain amplifier, said input radio-frequency interference filter circuit including at least one resistive component and at least one capacitive component configured to reduce differential and common-mode radio frequency interference present in said received electrical signals.
4 . The apparatus of claim 1 wherein said interface further includes a second amplifier circuit coupled between said first amplifier circuit and said processing system, said second amplifier circuit configured to provide a bandpass filter and gain function for said representation of said electrical signals.
5 . The apparatus of claim 4 wherein said second amplifier circuit includes a first amplification stage and a second amplification stage, said first stage having a gain of 300× and said second stage having a gain of 2×.
6 . The apparatus of claim 4 wherein said second amplifier circuit is configured to include passband corners of 2 Hz and 1000 Hz.
7 . The apparatus of claim 2 wherein said common mode cancellation amplifier circuit includes a high-pass filter circuit for receiving said common mode signal, a unity gain buffer operatively coupled to receive an output of said high-pass filter circuit, and a low-pass filter and gain stage operatively coupled to said unity gain buffer, said low-pass filter and gain stage configured to output a reference signal for cancelling common-mode voltage present at a source of said external electrical signals.
8 . The apparatus of claim 1 wherein external signals include at least one signal selected from a set of external signals including an EEG signal, an ECG signal, and an AEP signal.
9 . The apparatus of claim 1 wherein said digital hardware is further configured with said at least one software algorithm to generate an index value representative of a patient EEG and an index value representative of a patient AEP.
10 . The apparatus of claim 1 wherein said processing system is further configured for processing said representations of said received external signals utilizing wavelet signal processing procedures.
11 . The apparatus of claim 1 further including an isolated power supply module.
12 . The apparatus of claim 11 wherein said isolated power supply module includes a DC-DC converter having a switching frequency selected to minimize interference in the frequency bandwidth of signals acquired from the patient.
13 . The apparatus of claim 1 wherein said external signals are received from an integrated sensor suite, said integrated sensor suite configured to receive at least one external signal selected from a set of external signals including an EEG signal, and ECG signal, and AEP signal, and a pulse oximetry signal.
14 . The apparatus of claim 1 wherein said interface includes a circuit supplying an impedance check signal.
15 . The apparatus of claim 14 wherein said impedance check signal circuit is configured to enable automated checking of a patient electrode/skin interface impedance.
16 . The apparatus of claim 15 wherein said interface is operatively coupled to a patient with a low effective impedance to reduce signal noise caused by alternating current potentials.
17 . The apparatus of claim 1 wherein said interface is an analog interface; and wherein said processing system includes an analog to digital converter for digitizing signals received from said interface.
18 . The apparatus of claim 1 further including a battery power supply operatively coupled to supply power to said processing system and to said interface.
19 . The apparatus of claim 18 wherein said battery power supply, said processing system, and said interface are contained within a handheld enclosure.