Voltage sensing system with input impedance balancing for electrocardiogram (ECG) sensing applications
First Claim
1. An apparatus for sensing signals relative to a voltage at a ground node, the apparatus comprising:
- first, second, third, fourth, control, and ground nodes;
a first series impedance providing a first gain between the first and third nodes;
a first shunt impedance between the third and ground nodes;
a second series impedance providing a second gain between the second and fourth nodes;
a second shunt impedance between the fourth and control nodes;
a differential amplifier having inputs coupled to the third and fourth nodes and an output representative of a differential signal;
a common mode amplifier having inputs coupled to the third and fourth nodes and an output representative of a common mode signal; and
a control circuit, coupled to the differential amplifier output to receive the differential signal and coupled to the common mode amplifier to receive the common mode signal, the control circuit also coupled to the control node for providing a control signal such that a first gain between the first and third nodes approximately matches a second gain between the second and fourth nodes.
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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.
43 Citations
30 Claims
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1. An apparatus for sensing signals relative to a voltage at a ground node, the apparatus comprising:
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first, second, third, fourth, control, and ground nodes;
a first series impedance providing a first gain between the first and third nodes;
a first shunt impedance between the third and ground nodes;
a second series impedance providing a second gain between the second and fourth nodes;
a second shunt impedance between the fourth and control nodes;
a differential amplifier having inputs coupled to the third and fourth nodes and an output representative of a differential signal;
a common mode amplifier having inputs coupled to the third and fourth nodes and an output representative of a common mode signal; and
a control circuit, coupled to the differential amplifier output to receive the differential signal and coupled to the common mode amplifier to receive the common mode signal, the control circuit also coupled to the control node for providing a control signal such that a first gain between the first and third nodes approximately matches a second gain between the second and fourth nodes. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for sensing signals relative to a voltage at a ground node, the apparatus comprising:
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first, second, third, fourth, control, and ground nodes;
a first series impedance providing a first phase between the first and third nodes;
a first shunt impedance between the third and ground nodes;
a second series impedance providing a second phase between the second and fourth nodes;
a second shunt impedance between the fourth and control nodes;
a differential amplifier having inputs coupled to the third and fourth nodes and an output representative of a differential signal;
a common mode amplifier having inputs coupled to the third and fourth nodes and an output representative of a common mode signal; and
a control circuit, coupled to the differential amplifier output to receive the differential signal and coupled to the common mode amplifier to receive the common mode signal, the control circuit also coupled to the control node for providing a control signal such that a first phase between the first and third nodes approximately matches a second phase between the second and fourth nodes. - View Dependent Claims (8, 9, 10, 11, 12)
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13. An apparatus for sensing signals relative to a voltage at a ground node, the apparatus comprising:
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first, second, third, fourth, control, and ground nodes;
a first series impedance providing a first gain between the first and third nodes;
a first shunt impedance between the third and ground nodes;
a second series impedance providing a second gain between the second and fourth nodes;
a second shunt impedance between the fourth and control nodes;
a differential amplifier having inputs coupled to the third and fourth nodes and an output representative of a differential signal;
a common mode amplifier having inputs coupled to the third and fourth nodes and an output representative of a common mode signal; and
a means, coupled to the differential amplifier output to receive the differential signal and coupled to the common mode amplifier to receive the common mode signal, the means also coupled to the control node, for providing a control signal such that a first gain between the first and third nodes approximately matches a second gain between the second and fourth nodes. - View Dependent Claims (14, 15, 16, 17, 18)
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19. An apparatus for sensing signals relative to a voltage at a ground node, the apparatus comprising:
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first, second, third, fourth, control, and ground nodes;
a first series impedance providing a first phase between the first and third nodes;
a first shunt impedance between the third and ground nodes;
a second series impedance providing a second phase between the second and fourth nodes;
a second shunt impedance between the fourth and control nodes;
a differential amplifier having inputs coupled to the third and fourth nodes and an output representative of a differential signal;
a common mode amplifier having inputs coupled to the third and fourth nodes and an output representative of a common mode signal; and
a means, coupled to the differential amplifier output to receive the differential signal and coupled to the common mode amplifier to receive the common mode signal, the means also coupled to the control node, for providing a control signal such that a first phase between the first and third nodes approximately matches a second phase between the second and fourth nodes. - View Dependent Claims (20, 21, 22, 23, 24)
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25. An apparatus for sensing signals relative to a voltage at a ground node, the apparatus comprising:
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first, second, third, fourth, control, and ground nodes;
a first series impedance providing a first gain and a first phase between the first and third nodes;
a first shunt impedance between the third and ground nodes;
a second series impedance providing a second gain and a second phase between the second and fourth nodes;
a second shunt impedance between the fourth and control nodes;
a differential amplifier having inputs coupled to the third and fourth nodes and an output representative of a differential signal;
a common mode amplifier having inputs coupled to the third and fourth nodes and an output representative of a common mode signal; and
a control circuit coupled to the differential amplifier for receiving the differential signal and coupled to the common mode amplifier for receiving the common mode signal, the control circuit also coupled to the control node for providing a control signal such that a first gain and phase between the first and third nodes approximately matches a second gain and phase between the second and fourth nodes. - View Dependent Claims (26, 27, 28, 29, 30)
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Specification