UltraScale architecture-based devices contain one CMT per I/O bank. The MMCMs serve as frequency synthesizers for a wide range of frequencies, and as jitter filters for either external or internal clocks, and deskew clocks.
Input multiplexers select the reference and feedback clocks from either the global clock I/Os or the clock routing or distribution resources. Each clock input has a programmable counter divider (D). The phase-frequency detector (PFD) compares both phase and frequency of the rising edges of both the input (reference) clock and the feedback clock. If a minimum High/Low pulse is maintained, the duty cycle is ancillary. The PFD is used to generate a signal proportional to the phase and frequency between the two clocks. This signal drives the charge pump (CP) and loop filter (LF) to generate a reference voltage to the VCO. The PFD produces an up or down signal to the charge pump and loop filter to determine whether the VCO should operate at a higher or lower frequency. When VCO operates at a frequency that is too high, the PFD activates a down signal causing the control voltage to be reduced, thus decreasing the VCO operating frequency. When the VCO operates at a frequency that is too low, an up signal increases voltage. The VCO produces eight output phases and one variable phase for fine-phase shifting. Each output phase can be selected as the reference clock to the output counters ( This Figure ). Each counter can be independently programmed for a given customer design. A special counter M is also provided. This counter controls the feedback clock of the MMCM, allowing a wide range of frequency synthesis.
In addition to integer divide output counters, MMCMs add a fractional counter for CLKOUT0 and CLKFBOUT.
