A common mode control circuit (400) for generating a control signal indicative of a common mode signal in first and second signals of a differential signal pair comprises a first charge control means (300) for varying, dependent on polarity of the first and second signals with respect to a threshold, charge on a capacitive element (250, 260, 270). The first charge control means (300) is operable to, in response to the first and second signals both switching polarity simultaneously from opposite polarities, maintain a direction of flow of the charge. The first charge control means (300) can be operable to, in response to the first and second signals both switching polarity simultaneously from opposite polarities and the flow of charge being zero, maintain the flow at zero.