Amplifier circuit to enable accurate measurement of small electrical signals

A method of operating an amplifier circuit, the method including:

• providing a resistor divider (RREF) comprising n resistive elements (rn) in series where n>1, wherein:
• the resistor divider (RREF) comprises two main nodes defined at each end thereof, namely a first main node (a) and a second main node (b);
• the resistor divider (RREF) also comprises two readout nodes (d1, d2), namely a first readout node (d1) and a second readout node (d2) ;
• the resistor divider (RREF) comprises resistor nodes (q) defined between adjacent resistive elements;
• an input current source (IREF) is connected to the first main node (a);
• the resistor divider (RREF) comprises two arrays of addressable switch elements, with a first array of switch elements provided between the respective resistive nodes (q) of the resistor divider (RREF) and the first readout node (d1) and with a second array of switch elements provided between the respective resistive nodes (q) of the resistor divider (RREF) and the second readout node (d2);
• and
• a state of the switch elements is controlled by a feedback signal (SFB) to be open or closed, the readout nodes (d1, d2) thus acting as selectable voltage taps connected to the resistive elements (rn);
• providing a differential pair of transistors (T1, T2) comprising a first transistor (T1) having at least four terminals and a second transistor (T2) having at least four terminals, wherein:
• source terminals of each of the transistors (T1, T2) are connected to the second main node (b);
• gate terminals of the transistors (T1, T2) are connected to respective input signals (v1, V2);
• drain terminals of the transistors (T1, T2) are connected to respective current sources (I1, I2), wherein a differential output signal (VOUT) is created between the drain terminals of the transistors (T1, T2) ;
• and
• bulk terminals of the transistors (T1, T2) are connected to the respective readout nodes (d1, d2), wherein a bulk terminal of the first transistor (T1) is connected to the first readout node (d1) and a bulk terminal of the second transistor (T2) is connected to the second readout node (d2);
• performing, by the amplifier circuit, a function of a difference amplifier in that the transistors (T1, T2) form a differential amplifier with the respective input signals (V1, V2) on their gate terminals;
• and
• affecting, by the bulk terminals of the transistors (T1, T2) , a transconductance of the respective transistors (T1, T2) so as to add or subtract a differential signal derived from the readout nodes (d1, d2) of the resistor divider (RREF) based on voltage signals generated by the operation of the resistor divider (RREF) determined by the feedback signal (SFB), the bulk terminals thereby being configured to function as secondary gates.