Axcelerator Family FPGAs
v2.8
2-63
Axcelerator Clock Management System
Introduction
Each member of the Axcelerator family6 contains eight
phase-locked loop (PLL) blocks which perform the
following functions:
Programmable Delay (32 steps of 250 ps)
Clock Skew Minimization
Clock Frequency Synthesis
Each PLL has the following key features:
Input Frequency Range – 14 to 200 MHz
Output Frequency Range – 20 MHz to 1 GHz
Output Duty Cycle Range – 45% to 55%
Maximum
Long-Term
Jitter
–
1%
or
100ps
(whichever is greater)
Maximum Short-Term Jitter – 50ps + 1% of Output
Frequency
Maximum Acquisition Time (lock) – 20s
Physical Implementation
The eight PLL blocks are arranged in two groups of four.
One group is located in the center of the northern edge
of the chip, while the second group is centered on the
southern edge. The northern group is associated with
the four HCLK networks (e.g. PLLA can drive HCLKA),
while the southern group is associated with the four CLK
networks (e.g. PLLE can drive CLKE).
Each PLL cell is connected to two I/O pads and a PLL
Cluster that interfaces with the FPGA core.
Figure 2-48illustrates a PLL block. The VCCPLL pin should be
connected to a 1.5V power supply through a 250
Ω
resistor. Furthermore, 0.1
μF and 10 μF decoupling
capacitors should be connected across the VCCPLL and
VCOMPPLL pins. Note: The VCOMPPLL pin should never be
The I/O pads associated with the PLL can also be
configured for regular I/O functions except when it is
used as a clock buffer. The I/O pads can be configured in
all the modes available to the regular I/O pads in the
same I/O bank. In particular, the [H]CLKxP pad can be
configured as a differential pair, single-ended, or
voltage-referenced standard. The [H]CLKxN pad can only
be used as a differential pair with [H]CLKxP.
The block marked “/i Delay Match” is a fixed delay equal
to that of the i divider. The “/j Delay Match” block has
the same function as its j divider counterpart.
6. AX2000-CQ256 does not support operation of the phase-locked loops. This is in order to support full pin compatibility with
RTAX2000S/SL-CQ256.
Figure 2-48 PLL Block Diagram
RefCLK
FB
Lock
6
DIVJ
CLK1
CLK2
FBMuxSel
DelayLine
DIVJ
LowFreq
Osc
56
3
Delay Line
PowerDown
Delay Line
PLL
/i Delay
Match
/j Delay
Match
/i
/j