Clock structure with calibration circuitry

An integrated circuit includes a clock circuit that may be used to provide clock signals to multiple input-output circuits. The integrated circuit may also include different clock structures. As an example, one of the clock structures may have multiple clock paths of substantially equal lengths while another clock structure may have a fly-by clock path. The multiple clock paths may be used to convey a subset of the clock signals to the input-output circuits. Similarly, the fly-by clock path may be used to transmit a second subset of the clock signals to the input-output circuits.