Control circuit for use with a four terminal sensor, and measurement system including such a control circuit

A system comprising:

• a sensor having a variable impedance;
• and
• a control circuit, the control circuit configured to provide an excitation signal to the variable impedance and to receive a signal indicative of a voltage across the variable impedance;
• wherein the control circuit includes:
• an multiple-stage amplifier configured to receive the signal and to adjust the excitation current based on a comparison of the signal and a reference voltage;
• and
• a feedback path of a first stage of the multiple-stage amplifier, the feedback path coupled between an input of the first stage and an output of the first stage, and the feedback path configured to provide a zero of a transfer characteristic of the control circuit at a frequency where the gain of the control circuit is greater than unity gain.

A control circuit configured to couple to a biological sensor, the control circuit comprising:

• an excitation output node configured to provide current for a variable impedance of the biological sensor;
• a sensor input configured to receive a signal indicative of a voltage across the variable impedance;
• a multiple-stage amplifier configured to receive the signal and to adjust an excitation voltage at the excitation output node based the signal;
• and
• wherein a first stage of the multiple-stage amplifier includes means for changing phase of a transfer function of the control circuit.