Automatic input impedance balancing for electrocardiogram (ECG) sensing applications
First Claim
1. An apparatus for sensing a difference between first and second input voltages, the apparatus comprising:
- a reference circuit, where the reference circuit includes an input receiving an amplified signal based on first input voltage, and an output providing a reference voltage;
a compensation circuit, where the compensation circuit includes an input receiving an amplified signal based on the second input voltage, and an output providing a compensated voltage based on reference voltage;
a first amplification circuit, where the first amplification circuit includes a first input receiving a signal based on the reference voltage, a second input receiving a signal based on the compensated voltage, and an output providing a differential output signal based on a difference between the signals of the first and second inputs of the first amplification circuit;
an averager circuit, where the averager circuit includes a first input receiving a signal based on the reference voltage, a second input receiving a signal based on the compensated voltage, and an output providing a common mode (CM) output signal based on the signals at the first and second inputs of the averager circuit; and
an impedance circuit means for adjusting an impedance of the compensation circuit, based on the signals received from the outputs of the first amplification circuit and the averager circuit for reducing an impact of the CM output signal on the output of the first amplification circuit.
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Abstract
A voltage sensing system includes input impedance balancing for electrocardiogram (ECG) sensing or other applications, providing immunity to common-mode noise signals while capable of use with two electrodes. Signals are received at first and second electrodes having associated impedances. An impedance circuit includes a feedback controller that adjusts an effective impedance associated with the second electrode based on a difference signal, a common mode signal, a phase-shifted (e.g., quadrature common mode) signal, and an impedance associated with the first electrode. As a result, signals associated with each electrode undergo a similar degree of gain/attenuation and/or phase-shift. This reduces common mode noise and enhances the signal-to-noise characteristics of a desired ECG or other output signal, without requiring the use of more than two electrodes.
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Citations
23 Claims
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1. An apparatus for sensing a difference between first and second input voltages, the apparatus comprising:
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a reference circuit, where the reference circuit includes an input receiving an amplified signal based on first input voltage, and an output providing a reference voltage;
a compensation circuit, where the compensation circuit includes an input receiving an amplified signal based on the second input voltage, and an output providing a compensated voltage based on reference voltage;
a first amplification circuit, where the first amplification circuit includes a first input receiving a signal based on the reference voltage, a second input receiving a signal based on the compensated voltage, and an output providing a differential output signal based on a difference between the signals of the first and second inputs of the first amplification circuit;
an averager circuit, where the averager circuit includes a first input receiving a signal based on the reference voltage, a second input receiving a signal based on the compensated voltage, and an output providing a common mode (CM) output signal based on the signals at the first and second inputs of the averager circuit; and
an impedance circuit means for adjusting an impedance of the compensation circuit, based on the signals received from the outputs of the first amplification circuit and the averager circuit for reducing an impact of the CM output signal on the output of the first amplification circuit. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for sensing a difference between first and second input voltages, the apparatus comprises:
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a first input circuit, providing a first buffered input voltage based on a signal received from a first electrode;
a second input circuit, providing a second buffered input voltage based on a signal received from a second electrode;
a reference circuit, providing a reference voltage signal based on the first buffered input voltage;
a compensation circuit, providing a compensated voltage signal based on the reference voltage signal;
a first amplification circuit means for providing a differential output signal based on the reference and compensated voltage signals;
an averager circuit, providing a common mode (CM) output signal based on the reference and compensated input voltages; and
impedance circuit means for approximately matching at least one of a gain/attenuation or a phase of the reference circuit and the first electrode to at least one of a respective gain/attenuation or a phase of the compensation circuit and the second electrode based on the differential and CM output signals. - View Dependent Claims (8)
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9. A method of detecting first and second input signals, the method comprising the steps of:
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receiving the first input signal from a first electrode;
receiving the second input signal from a second electrode;
buffering the first input signal using impedance bootstrapping at a first input;
obtaining a difference signal based on the first and second input signals;
obtaining a common mode (CM) signal based on the first and second input signals;
obtaining a quadrature common mode (QCM) signal that is phase-shifted from the CM signal; and
varying an impedance at a second input in order to approximately match a gain/attenuation or a phase-of the second input signal to a respective gain/attenuation or a phase of the first input signal, based on the difference between the CM and QCM signals. - View Dependent Claims (10)
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11. A system, comprising:
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a first input circuit, providing a first input voltage based on a signal received from a first electrode;
a second input circuit, providing a second input voltage based on a signal received from a second electrode;
amplification circuit means for providing an electrocardiogram (ECG) output signal based on the first and second input voltages;
a right leg feedback electrode, operatively coupled to the amplification circuit to reduce common mode (CM) noise generated at the first and second electrodes; and
a switch means for operatively coupling the amplification circuit and the right leg feedback electrode and for selectively turning-off parasitic feedback coming from a right leg feedback electrode cable, when the right leg electrode is not being used. - View Dependent Claims (12, 13, 14)
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15. A method of using an electrocardiogram (ECG) system, comprising the steps of:
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receiving a first input signal from a first electrode;
receiving a second input signal from the second electrode;
inverting and multiplying a common mode drive signal received from a right leg feedback electrode when the right leg electrode is being used;
disconnecting a right leg drive signal from a right leg ECG cable when the right leg feedback electrode is not being used;
obtaining a difference signal based on the first and second input signals; and
displaying the difference signal as ECG output signal. - View Dependent Claims (16, 17)
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18. An apparatus for sensing a difference between first and second input voltages, comprising:
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a first amplification circuit, including a first input receiving a signal based on a first input voltage, a second input receiving a signal based on a second input voltage, and an output providing a differential output signal based on a difference between the signals at the first and second inputs of the amplification circuit;
an averager circuit, including a first input receiving a signal based on the first input voltage, a second input receiving a signal based on the second input voltage, and an output providing a common mode (CM) output signal based on the signals at the first and second inputs to the averager circuit;
an automatic gain control circuit means, including a first input for receiving the common mode output signal from the averager circuit, and an output for providing an amplitude regulated common mode signal;
a phase-shifter circuit, operatively coupled to the output of the automatic gain control circuit to receive the amplitude regulated CM output signal, and provide a quadrature common mode (QCM) output signal; and
an impedance circuit means, coupled for receiving signals from the outputs of the first amplification and the phase-shifter circuits, and where the impedance circuit means is adapted for adjusting an impedance, coupled to the second input voltage, based on the signals received from the outputs of the first amplification circuit and the phase-shifter circuit. - View Dependent Claims (19)
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20. A method of detecting a voltage between first and second electrodes, the method comprising the steps of:
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receiving a first input voltage from the first electrode;
receiving a second input voltage from the second electrode;
obtaining a difference signal based on the first and second input voltages;
obtaining a common mode (CM) signal based on the first and second input voltages where the CM signal includes a transient response time;
regulating amplitude of the CM signal such that the transient response time is essentially constant over input noise levels;
obtaining a quadrature common mode (QCM) signal that is phase shifted from the regulated CM signal;
multiplying components of the regulated common mode signal with the difference signal to provide a first control signal;
multiplying components of the difference signal with the components of the QCM signal to provide a second control signal; and
varying an impedance coupled to the second electrode to approximately match a gain/attenuation or a phase of the second control signal to at least one of respective gain/attenuation or phase of the first control signal, based on a difference between regulated CM and QCM signals. - View Dependent Claims (21)
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22. A method of using an electrocardiogram to detect first and second input signals, the method comprising the steps of:
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receiving the first input signal from a first electrode;
receiving the second input signal form a second electrode obtaining a difference signal based on the first and second input signals;
obtaining a common mode (CM) signal based on the first and second input signals;
regulating amplitude of the CM signal to keep a transient response time essentially constant for input noise levels;
obtaining a quadrature common mode (QCM) signal that is phase-shifted from the CM signal; and
matching at least one of a gain/attenuation or a phase of the second input signal to at least one of respective gain/attenuation or phase of the first input signal, based on a difference between regulated CM and QCM signals. - View Dependent Claims (23)
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Specification