Circuit for impedance measurements

An impedance sensor comprising:

• a front-end circuit;
• and
• two electrodes, whereby one of the two electrodes is connected to the first input-terminal and the other of the two electrodes is connected to the second input-terminal and whereby the front-end circuit is arranged in a sensor head and the two electrodes are arranged in a sensor body and whereby the sensor head is mounted to the sensor body;
• wherein the front-end circuit comprises:
• a. an excitation-terminal, intended to receive an excitation signal relative to a common ground;
• b. a first and a second input-terminal, intended to be connected to two electrodes;
• c. an operational amplifier comprising:
• i. an inverting input;
• and
• ii. an Op-Amp output;
• d. a switching unit, wherein a state of the switching unit determines an operation of the operational amplifier;
• wherein the front-end circuit is configured to, when in use such that electrodes are connected to the first and the second input terminal while a sample is arranged between the electrodes and while the excitation signal is received at the excitation-terminal:
• cause, by the excitation signal and depending on the state of the switching unit, one of:
• 1. A current flowing through the electrodes and the sample, and
• 2. a voltage across the electrodes and the sample.

A front-end circuit for impedance measurement comprising:

• a. an excitation-terminal, intended to receive an excitation signal relative to a common ground;
• b. a first and a second input-terminal, intended to be connected to two electrodes;
• c. an operational amplifier comprising:
• i. a non-inverting input connected to the common ground,
• ii. an inverting input, and
• iii. an Op-Amp output;
• d. a switching unit, wherein a state of the switching unit determines an operation of the operational amplifier, and wherein the switching unit comprises a first and a second mode selection-switch-unit, wherein:
• i. the first mode selection-switch-unit comprises:
• 1. A first mode switch-input connected to the Op-Amp output, and
• 2. a second mode switch-input connected to the excitation-terminal,
• ii. the second mode selection-switch-unit comprises:
• 3. the first mode switch-input connected to the excitation terminal, and
• 4. the second mode switch-input connected to the Op-Amp output, and
• iii. each of the first and second mode selection-switch-unit comprises a switch-output, wherein a state of the mode selection-switch-unit determines whether the first mode switch-input or the second mode switch-input is connected to the switch-output,
• e. a first and a second output-terminal, wherein:
• i. the switch-output of the first mode selection-switch-unit is connected to the first input-terminal and the first output-terminal, and
• ii. the switch-output of the second mode selection-switch-unit is connected to a first resistor terminal of a reference resistor and the second output-terminal;
• and
• f. the reference resistor comprising the first resistor terminal and a second resistor terminal, wherein the second resistor terminal of the reference resistor is connected to the inverting input of the operational amplifier and the second input-terminal.