5–10
Chapter 5: Clock Networks and PLLs in the Cyclone III Device Family
Cyclone III Device Family PLL Hardware Overview
Cyclone III Device Family PLL Hardware Overview
This section gives a hardware overview of the Cyclone III device family PLL.
Figure 5–6 shows a simplified block diagram of the major components of the PLL of
the Cyclone III device family.
(1)
Figure 5–6. Cyclone III Device Family PLL Block Diagram
lock
LOCK
circuit
÷C0
÷C1
÷C2
Clock inputs
from pins
4
8
÷n
clkswitch
8
÷2 (2)
inclk0
inclk1
LF
VCO
PFD
CP
Clock
Switchover
Block
PLL
output
mux
clkbad0
GCLKs
÷C3
÷C4
GCLK(3)
clkbad1
VCO
Range
Detector
VCOOVRR
VCOUNDR
External clock
output
activeclock
pfdena
÷M
no compensation;
ZDB mode
GCLK
networks
source-synchronous;
normal mode
Notes to Figure 5–6:
(1) Each clock source can come from any of the four clock pins located on the same side of the device as the PLL.
(2) This is the VCO post-scale counter K.
(3) This input port is fed by a pin-driven dedicated GCLK, or through a clock control block if the clock control block is fed by an output from another
PLL or a pin-driven dedicated GCLK. An internally generated global signal cannot drive the PLL.
1
The VCO post-scale counter K is used to divide the supported VCO range by two. The
VCO frequency reported by the Quartus II software in the PLL summary section of
the compilation report takes into consideration the VCO post-scale counter value.
Therefore, if the VCO post-scale counter has a value of 2, the frequency reported is
lower than the fVCO specification specified in the Cyclone III Device Data Sheet and
Cyclone III LS Device Data Sheet chapters.
External Clock Outputs
Each PLL of the Cyclone III device family supports one single-ended clock output or
one differential clock output. Only the C0 output counter can feed the dedicated
external clock outputs, as shown in Figure 5–7, without going through the GCLK.
Other output counters can feed other I/O pins through the GCLK.
Cyclone III Device Handbook
Volume 1
July 2012 Altera Corporation
ALTERA [ ALTERA CORPORATION ]
