Reconfigurable sensor circuit

1. A reconfigurable sensor circuit comprising:

an input stage including a first input terminal and a second input terminal, and

an amplification stage including:

a first amplifier having a non-inverting input, an inverting input, and an output, the output of the first amplifier connected to the inverting input of the first amplifier via a first resistor,

a second amplifier having a non-inverting input, an inverting input, and an output, the output of the second amplifier connected to the inverting input of the second amplifier via a second resistor, and

first switching circuitry adapted to be arranged in a first state, wherein the amplification stage is in a differential amplifier configuration, and in a second state, wherein the amplification stage is in a transimpedance amplifier configuration,

wherein, in the differential amplifier configuration, the first amplifier and the second amplifier are together configured as a differential amplifier connected to the first and the second input terminals, wherein the non-inverting input of the first amplifier is connected to the first input terminal and the non-inverting input of the second amplifier is connected to the second input terminal, and the inverting input of the first amplifier is connected to the inverting input of the second amplifier via at least one resistor, and

wherein, in the transimpedance amplifier configuration, at least the first amplifier is configured as a transimpedance amplifier connected to the first input terminal.

2. A circuit according to claim 1 , wherein, in the transimpedance amplifier configuration, the inverting input of the first amplifier is connected to the first input terminal.

3. A circuit according to claim 1 , further comprising:

an analog-to-digital conversion stage having a first input and a second input, and

second switching circuitry adapted to be arranged in a first state wherein the first input of the analog-to-digital conversion stage is connected to the output of the first amplifier and the second input of the analog-to-digital conversion stage is connected to the output of the second amplifier, and in a second state wherein the first input of the analog-to-digital conversion stage is connected to the output of the first amplifier and the second input of the analog-to-digital conversion stage is connected to a voltage reference input.

4. A circuit according to claim 1 , further comprising a DC voltage buffer arranged to output a DC voltage via a terminal of the circuit.

5. A circuit according to claim 1 , further comprising a controlled DC voltage source switchably connected, via said first switching circuitry, to the non-inverting input of the first amplifier.

6. A circuit according to claim 1 , further comprising:

a first current source arranged to feed an AC current to a current output terminal, and

a second current source arranged to draw an AC current from a current input terminal.

7. A circuit according to claim 1 , further comprising a demodulator connected to the first input terminal and the second input terminal.

8. A circuit according to claim 1 , further comprising a first high-pass filter switchably connected to the first input terminal and a second high-pass filter switchably connected to the second input terminal.

9. A system for electrical measurements on a body of a user, comprising:

a circuit according to claim 1 ;

a set of skin electrodes connected to the terminals of the circuit.

10. A system according to claim 9 , wherein said set of skin electrodes includes a first skin electrode connected to the first input terminal of the circuit, a second skin electrode connected to the second input terminal of the circuit, a third skin electrode connected to the third terminal of the circuit, and a pair of skin electrodes connected to the current output terminal and current input terminal of the circuit.

11. A method of performing electrical measurements on a body of a user using a system for electrical measurements on a body of a user, the system comprising:

a reconfigurable sensor circuit comprising:

an input stage including a first input terminal and a second input terminal, and

an amplification stage including:

a first amplifier having a non-inverting input, an inverting input, and an output, the output of the first amplifier connected to the inverting input of the first amplifier via a first resistor,

a second amplifier having a non-inverting input, an inverting input, and an output, the output of the second amplifier connected to the inverting input of the second amplifier via a second resistor, and

first switching circuitry adapted to be arranged in a first state, wherein the amplification stage is in a differential amplifier configuration, and in a second state, wherein the amplification stage is in a transimpedance amplifier configuration,

wherein, in the differential amplifier configuration, the first amplifier and the second amplifier are together configured as a differential amplifier connected to the first and the second input terminals, wherein the non-inverting input of the first amplifier is connected to the first input terminal and the non-inverting input of the second amplifier is connected to the second input terminal, and the inverting input of the first amplifier is connected to the inverting input of the second amplifier via at least one resistor, and

wherein, in the transimpedance amplifier configuration, at least the first amplifier is configured as a transimpedance amplifier connected to the first input terminal; and

the system further comprising a set of skin electrodes connected to the terminals of the circuit.

12. A method in accordance with claim 11 , further comprising:

configuring the circuit in a voltage sensing mode by setting the amplification stage in the differential amplification configuration and switching the second switching circuitry to the first state, and

measuring a voltage difference between a first skin electrode connected to the first input terminal of the circuit and a second skin electrode connected to the second input of the circuit.

13. A method in accordance with claim 11 , further comprising

configuring the circuit in a current sensing mode by setting the amplification stage in the transimpedance amplification configuration, switching the second switching circuitry to the second state; and

measuring a current between a first skin electrode connected to the first input terminal of the circuit and a third skin electrode connected to the third terminal of the circuit.

14. A method in accordance with claim 11 , further comprising: configuring the circuit in an impedance sensing mode by setting the amplification stage in the differential amplification configuration and switching the second switching circuitry to the first state,

driving a current between the current output terminal and the current input terminal through the body of the user, and

measuring an impedance between a first skin electrode connected to the first input terminal of the circuit and a second skin electrode connected to the second input of the circuit.