Patent ID: 10240968

Abstract:
A differential measurement circuit (1) is implemented in a balance with electromagnetic force compensation. The circuit receives input from two photo currents (I1, I2) generated by photodiodes (D1, D2) and generates an output signal proportional to their difference. A switch (SW) controls the flow of current through a node (KΔ) to which the two photo currents are directed, by flipping between two states (zt1, zt2) within two phases (t1, t2) of a time period T. The switch is controlled so a reference current (IRef) from a voltage or current source (URef) is superimposed alternatingly within the time phases on one of the two photo currents which continuously flow into the node. The node lies at the input of an integrator (INT) whose integrator signal (sINT) can be compared in a comparator (CMP) to a cyclically recurring ramp signal (sRAMP) which conforms to the time period. At the output of the comparator, a rectangular-shaped comparator signal (sPWM) can be generated whose duty cycle ratio is defined by the intersection of the integrator signal with the ramp signal and which can be directed to a control input of the switch.