An integrated electrical filter includes resistors (R10-12) and capacitors (C10-12). The capacitors are controllable in value by means of a control circuit (100-109) and are formed by a binary weighted array of capacitor elements which are selectively connectable in parallel. A controlled oscillator (103 Figure 1) or a controlled phase shifting network (113 Figure 2) includes a capacitor of the same form as the filter capacitors. The oscillator (103) or phase shifter (113) form part of a phase locked loop (101, 104, 105, 107) which produces a digital code as its control signal at the output of an up/down counter (107). This digital code is latched in a register (109) to provide a control signal for the filter capacitors and is used directly to control the capacitor(s) in the controlled oscillator or phase shifter.