Chopper-stabilized instrumentation amplifier for impedance measurement

A biological impedance sensing device comprising:

• 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.

A method for sensing impedance of a biological load, the method comprising:

• 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.

An implantable medical device comprising:

• 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.