A circuit converts a single-ended signal to differential signals that are balanced to have the same amplitudes and opposite phases. The circuit includes a balance tunable balun, a detector, and a controller. The balance tunable balun has a primary winding, a secondary winding, a control input, and a switched resistor-capacitor (RC) network. The primary winding receives the single-ended signal and the secondary winding outputs the differential signals. The control input receives a control signal and the switched RC network tunes an output imbalance of the balun responsive to this control signal. The detector detects the output imbalance and the controller generates the control signal to control the switched RC network to reduce that output imbalance. The circuit produces well balanced differential signals over a wide range of signal frequencies, even when asymmetries, process variations, or parasitic capacitance in the balun would otherwise result in imbalance.