Two directional voltages in mutual phase opposition corresponding to the degree and direction of detuning are applied to the base electrodes of corresponding ones of first and second input transistors. Each of the first and second input transistors has a collector electrode connected to a source of supply voltage and an emitter electrode connected to a source of reference voltage via a corresponding one of a pair of ohmic emitter resistors. First and second output transistors are connected in parallel with each other in opposite conductance directions between the emitter electrodes of the input transistors. Each of the first and second output transistors has an emitter electrode directly connected to the emitter electrode of a corresponding one of the input transistors, a collector electrode connected to the emitter electrode of a corresponding one of the input transistors via a corresponding one of one of two pairs of ohmic resistors and a base electrode connected to the emitter electrode of a corresponding one of the input transistors via a corresponding one of the other of the two pairs of ohmic resistors. An output magnitude corresponding to the trimming voltage is derived from the collector electrodes of the output transistors.