In circuitry to capture differences between magnitudes of first and second comparator input signals in capture operations defined by a clock signal, first and second nodes are connectable to a tail node receiving a cock-signal-independent bias current along first and second paths. During each capture operation, switching circuitry controls connections between the tall node and the first and second nodes based on the input signals to divide the bias current between the first and second paths depending on the input signal magnitude difference. The switching circuitry comprises first and second transistors arranged such that conductivity of connections between the tail node and the first and second nodes Is controlled by the magnitudes of the input signals, and third and fourth non-clocked transistors controlled by a clock-signal independent gate bias signal.