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Ixiasoft
4. I/O PLL Parameterizable Macro (ipm_iopll)
I/O PLL parameterizable macro allows you to readily configure the settings of the I/O PLL. An I/O PLL is a frequency-control system that generates an output clock by synchronizing itself to an input clock. The PLL compares the phase difference between the input signal and the output signal of a voltage-controlled oscillator (VCO) and then performs phase synchronization to maintain a constant phase angle (lock) on the frequency of the input or reference signal. The synchronization or negative feedback loop of the system forces the PLL to be phase locked.
You can configure PLLs as frequency multipliers, dividers, demodulators, tracking generators, or clock recovery circuits. You can use PLLs to generate stable frequencies, recover signals from a noisy communication channel, or distribute clock signals throughout your design.
The I/O PLL macro (ipm_iopll) generates up to seven output clock frequencies with respect to the input reference clock, and can generate up to nine clock output signals. The generated clock output signals clock the core or the external blocks outside the core. Computation codes are used to calculate the expected clock frequencies and to compute the physical parameter values (divide N counter, divide M counter and divide C counters) of the I/O PLL for functional correctness.
The PLL lock is dependent on the two input signals in the phase frequency detector. The lock signal is an asynchronous output of the PLLs. The number of cycles required to gate the lock signal depends on the PLL input clock which clocks the gated-lock circuitry. Divide the maximum lock time of the PLL by the period of the PLL input clock to calculate the number of clock cycles required to gate the lock signal
The ipm_iopll macro supports the following:
- Supports removal of added delays in the feedback clock network by selecting the suitable compensation or operation modes.
- Supports various clock feedback operating modes to compensate for clock network delays to align the rising edge of the output clock with the rising edge of the PLL’s reference clock, as I/O PLL Parameterizable Macro Operating Modes describes
- Supports variable phase shifts of outclks. Currently supported phase shifts in the macro are 0, 90, 180 and 270 degrees.
This section provides the port descriptions, parameter tables, and instantiation templates for this parameterizable macro.