Chopper-stabilized instrumentation amplifier for impedance measurement
First Claim
1. A biological impedance sensing device comprising:
- a current source configured to generate a modulated current at a modulation frequency for application across a biological load to produce an input signal;
an amplifier configured to amplify the input signal to produce an amplified signal;
a demodulator configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load;
a modulator configured to modulate an amplitude of the output signal at the modulation frequency to produce a modulated output signal; and
a feedback path that applies the modulated output signal as a feedback signal to the input signal.
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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.
107 Citations
25 Claims
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1. A biological impedance sensing device comprising:
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a current source configured to generate a modulated current at a modulation frequency for application across a biological load to produce an input signal; an amplifier configured to amplify the input signal to produce an amplified signal; a demodulator configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load; a modulator configured to modulate an amplitude of the output signal at the modulation frequency to produce a modulated output signal; and a feedback path that applies the modulated output signal as a feedback signal to the input signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A biological impedance sensing device comprising:
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means for applying a current modulated at a modulation frequency across a biological load to produce an input signal; means for amplifying the input signal to produce an amplified signal; means for demodulating an amplitude of the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load; means for modulating an amplitude of the output signal at the modulation frequency to produce a modulated output signal; and means for applying the modulated output signal as a feedback signal to the input signal. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A method for sensing impedance of a biological load, the method comprising:
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applying a current modulated at a modulation frequency across a biological load to produce an input signal; amplifying the input signal with an amplifier to produce an amplified signal; demodulating an amplitude of the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load; modulating an amplitude of the output signal at the modulation frequency to produce a modulated output signal; and applying the modulated output signal as a feedback signal to the input signal. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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23. An implantable medical device comprising:
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a therapy delivery module configured to deliver a therapy to a patient; a sensor comprising; a current source configured to generate a modulated current at a modulation frequency for application across a biological load to produce an input signal, an amplifier configured to amplify the input signal to produce an amplified signal, a demodulator configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load, a modulator configured to modulate an amplitude of the output signal at the modulation frequency to produce a modulated output signal, and a feedback path that applies the modulated output signal as a feedback signal to the input signal; and a processor configured to control the therapy delivery module and process a representation of the output signal produced by the sensor. - View Dependent Claims (24, 25)
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Specification