3.1.2. ATX PLL
Input Reference Clock
This is the dedicated input reference clock source for the PLL.
The input reference clock can be sourced from one of the following:
- Dedicated reference clock pin
- Reference clock network
- Receiver input pin
- Output of another PLL with PLL cascading
- Global clock or the core clock network
Sourcing reference clock from a cascaded PLL output, global clock or core clock network introduces additional jitter to the ATX PLL output. Refer to KDB "How do I compensate for the jitter of PLL cascading or non-dedicated clock path for Arria® 10 PLL reference clock?" for more details.
The ATX PLL calibration is clocked by the CLKUSR clock which must be stable and available for calibration to proceed. Refer to the Calibration section for more details about the CLKUSR clock.
Reference Clock Multiplexer
The reference clock (refclk) multiplexer selects the reference clock to the PLL from the various reference clock sources available.
The N counter divides the refclk mux's output. The division factors supported are 1, 2, 4, and 8.
Phase Frequency Detector (PFD)
The reference clock(refclk) signal at the output of the N counter block and the feedback clock (fbclk) signal at the output of the M counter block are supplied as inputs to the PFD. The output of the PFD is proportional to the phase difference between the refclk and fbclk inputs. It is used to align the refclk signal at the output of the N counter to the feedback clock (fbclk) signal. The PFD generates an "Up" signal when the reference clock's falling edge occurs before the feedback clock's falling edge. Conversely, the PFD generates a "Down" signal when the feedback clock's falling edge occurs before the reference clock's falling edge.
Charge Pump and Loop Filter
The PFD output is used by the charge pump and loop filter (CP and LF) to generate a control voltage for the VCO. The charge pump translates the "Up" or "Down" pulses from the PFD into current pulses. The current pulses are filtered through a low pass filter into a control voltage that drives the VCO frequency. The charge pump, loop filter, and VCO settings determine the bandwidth of the ATX PLL.
The lock detector block indicates when the reference clock and the feedback clock are phase aligned. The lock detector generates an active high pll_locked signal to indicate that the PLL is locked to its input reference clock.
Voltage Controlled Oscillator
The voltage controlled oscillator (VCO) used in the ATX PLL is LC tank based. The output of charge pump and loop filter serves as an input to the VCO. The output frequency of the VCO depends on the input control voltage. The output frequency is adjusted based on the output voltage of the charge pump and loop filter.
L CounterThe L counter divides the differential clocks generated by the ATX PLL. The L counter is not in the feedback path of the PLL.
M CounterThe M counter's output is the same frequency as the N counter's output. The VCO frequency is governed by the equation:
VCO freq = 2 * M * input reference clock/N
An additional divider divides the high speed serial clock output of the VCO by 2 before it reaches the M counter.
The M counter supports division factors in a continuous range from 8 to 127 in integer frequency synthesis mode and 11 to 123 in fractional mode.
Delta Sigma Modulator
The fractional mode is only supported when the ATX PLL is configured as a cascade source for OTN and SDI protocols. The delta sigma modulator is used in fractional mode. It modulates the M counter divide value over time so that the PLL can perform fractional frequency synthesis. In fractional mode, the M value is as follows: .
M (integer) + K/2^32, where K is the Fractional multiply factor (K) in the ATX PLL IP Parameter Editor
K legal values are 1 through 2^32-1 and can only be manually entered in the ATX PLL IP Parameter Editor in Quartus Prime software.
The output frequencies can be exact when the ATX PLL is configured in fractional mode. Due to the K value 32-bit resolution, translating to 1.63 Hz step for a 7 GHz VCO frequency, not all desired fractional values can be achieved exactly. The lock signal is not available, when configured in fractional mode in k-precision mode (K < 0.1 or K > 0.9).
Multiple Reconfiguration Profiles
Under the ATX PLL IP Parameter Editor Dynamic Reconfiguration tab, in the Configuration Profiles section, multiple reconfiguration profiles can be enabled. This allows to create, store, and analyze the parameter settings for multiple configurations or profiles of the ATX PLL IP.
The ATX PLL IP GUI can generate configuration files (SystemVerilog, C header or MIF) for a given configuration. With the multi reconfiguration profile options enabled, the ATX PLL IP Parameter Editor can produce configuration files for all of the profiles simultaneously. In addition, by enabling the reduced reconfiguration files generation, t