Chopper-stabilized instrumentation amplifier for impedance measurement

A chopper-stabilized instrumentation amplifier comprising:

• means for generating an alternating current (ac) stimulation current at a clock frequency for application to a load, wherein the application of the stimulation current to the load produces an input signal;
• means for amplifying the input signal to produce an amplified signal;
• means for demodulating the amplified signal at the clock frequency to produce an output signal;
• means for modulating an amplitude of the output signal at the clock frequency;
• and
• means for applying the modulated output signal as a feedback signal to the input signal.

A method comprising:

• generating an alternating current (ac) stimulation current at a clock frequency;
• applying the stimulation current to a load to produce an input signal;
• amplifying the input signal in a mixer amplifier to produce an amplified signal;
• demodulating the amplified signal in the mixer amplifier at the clock frequency to produce an output signal;
• modulating an amplitude of the output signal at the clock frequency to produce a feedback signal;
• and
• applying the modulated output signal as a feedback signal to the input signal via a first feedback path.

A biomedical impedance sensing device comprising:

• an alternating current (ac) source that generates an ac stimulation current at a clock frequency for application to a biological load;
• a mixer amplifier coupled to receive an input signal from the load in response to the stimulation current, wherein the mixer amplifier amplifies the input signal to produce an amplified signal and demodulates the amplified signal at the clock frequency to produce an output signal;
• a modulator that modulates an amplitude of the output signal at the clock frequency;
• and
• a feedback path that applies the modulated output signal as a feedback signal to the input signal.