Visible to Intel only — GUID: mcn1395712669789
Ixiasoft
Visible to Intel only — GUID: mcn1395712669789
Ixiasoft
2.3.1. PLL Architecture
The main purpose of a PLL is to synchronize the phase and frequency of the voltage-controlled oscillator (VCO) to an input reference clock.
Phase-Frequency Detector (PFD)
The PFD has inputs from the feedback clock, fFB, and the input reference clock, fREF. The PLL compares the rising edge of the input reference clock to a feedback clock using a PFD. The PFD produces an up or down signal that determines whether the VCO needs to operate at a higher or lower frequency.
Charge Pump (CP)
If the charge pump receives a logic high on the up signal, current is driven into the loop filter. If the charge pump receives a logic high on the down signal, current is drawn from the loop filter.
Loop Filter (LF)
The loop filter converts the up and down signals from the PFD to a voltage that is used to bias the VCO. The loop filter filters out glitches from the charge pump and prevents voltage overshoot, which minimizes jitter on the VCO.
Voltage-Controlled Oscillator (VCO)
The voltage from the charge pump determines how fast the VCO operates. The VCO is implemented as a four-stage differential ring oscillator. A divide counter, M, is inserted in the feedback loop to increase the VCO frequency, fVCO, above the input reference frequency, fREF.
The VCO frequency is determined using the following equation:
fVCO = fREF × M = fIN × M/N ,
where fIN is the input clock frequency to the PLL and N is the pre-scale counter.
The VCO frequency is a critical parameter that must be between 600 and 1,300 MHz to ensure proper operation of the PLL. The Intel® Quartus® Prime software automatically sets the VCO frequency within the recommended range based on the clock output and phase shift requirements in your design.
Post-Scale Counters (C)
The VCO output can feed up to five post-scale counters (C0, C1, C2, C3, and C4). These post-scale counters allow the PLL to produce a number of harmonically-related frequencies.
Internal Delay Elements
The Intel® MAX® 10 PLLs have internal delay elements to compensate for routing on the GCLK networks and I/O buffers. These internal delays are fixed.
PLL Outputs
The Intel® MAX® 10 PLL supports up to 5 GCLK outputs and 1 dedicated external clock output. The output frequency, fOUT, to the GCLK network or dedicated external clock output is determined using the following equation:
fREF = fIN/N and
fOUT = fVCO/C = (fREF × M)/C = (fIN × M)/(N × C),
where C is the setting on the C0, C1, C2, C3, or C4 counter.