Chopper-stabilized instrumentation amplifier for impedance measurement
First Claim
1. A medical device comprising:
- a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, wherein the current source comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current;
an amplifier configured to amplify the input signal to produce an amplified signal; and
a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.
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Abstract
This disclosure describes a chopper stabilized instrumentation amplifier. The amplifier is configured to achieve stable measurements at low frequency with very low power consumption. The instrumentation amplifier uses a differential architecture and a mixer amplifier to substantially eliminate noise and offset from an output signal produced by the amplifier. Dynamic limitations, i.e., glitching, that result from chopper stabilization at low power are substantially eliminated through a combination of chopping at low impedance nodes within the mixer amplifier and feedback. The signal path of the amplifier operates as a continuous time system, providing minimal aliasing of noise or external signals entering the signal pathway at the chop frequency or its harmonics. The amplifier can be used in a low power system, such as an implantable medical device, to provide a stable, low-noise output signal.
158 Citations
24 Claims
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1. A medical device comprising:
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a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, wherein the current source comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current; an amplifier configured to amplify the input signal to produce an amplified signal; and a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A medical device comprising:
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means for applying a modulated current at a modulation frequency across a load to produce an input signal, wherein the means for applying comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current; means for amplifying the input signal to produce an amplified signal; and means for demodulating the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A method for sensing impedance of a load, the method comprising:
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switching, with a medical device, a current produced by a voltage source at a modulation frequency to produce a modulated current; applying, with the medical device, the modulated current at the modulation frequency across a load to produce an input signal; amplifying, with the medical device, the input signal with an amplifier to produce an amplified signal; and demodulating, with the medical device, an amplitude of the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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Specification