v3.0 15
ProASICPLUS Flash Family FPGAs
Timing Control and Characteristics
ProASICPLUS Clock Management System
Introduction
ProASICPLUS devices provide designers with very flexible
clock conditioning capabilities. Each member of the
ProASICPLUS family contains two phase-locked loop (PLL)
blocks which perform the following functions:
• Clock Phase Adjustment via Programmable Delay (250 ps
steps from –8 ns to +8 ns)
• Clock Skew Minimization
• Clock Fre qu enc y Synth esi s
Each PLL has the following key features:
• Input Fre q ue nc y Ran ge (fIN) = 1.5 to 180 MHz
• Feedback Frequency Range (fVCO) = 1.5 to 180 MHz
• Outp ut F req ue nc y R an g e ( f OUT) = 6 to 18 0 M Hz
• Output Phase Shift = 0 °, 90 °, 180 °, and 270 °
• Output Duty Cycle = 50%
• Low Output Jitter (max at 25° C)
–f
VCO <10 MHz. Jitter ±1% or better
– 10 MHz < fVCO < 60 MHz. Jitter ±2% or better
–f
VCO > 60 MHz. Jitter ±1% or better
• Maximum Acquisition Time = 80µ s
• Low Power Consumption – 6.9 mW (max – analog supply)
+ 7.0µW/ MHz (m ax – d ig it a l su pp ly)
Physical Implementation
Each side of the chip contains a clock conditioning circuit
based upon a 180 MHz PLL block (Figure 14 on page16).
Two global multiplexed lines extend along each side of the
chip to provide b idirectional access to the PLL on that side
(neither MUX can be connected to the opposite side's PLL).
Each global line has optional LVPECL input pads
(described below). The global lines may be driven by eit her
the LVPECL global input pad or the outputs from the PLL
block or both. E ach global line can be driven by a different
output from the PLL. Unused global pi ns can be configured
as regular I/Os or left unconnected. They default to an input
with pull-up. The two signals available to drive the global
networks are as follows (Figure 15 on page 17):
Global A (secondary clock)
• Output from Global MUX A
• Condition ed ve r s i on of PLL outp ut ( f OUT) – delayed or
advanced
• Divided version of either of the above
• Further delayed version of either of the above (0.25 ns,
0.50 ns, or 4.00 ns delay)1
Global B
• Output from G lobal MUX B
• Delayed or advanced version of fOUT
• Divided version of either of the above
• Further delayed version of either of the above (0.25 ns,
0.50 ns, or 4.00 ns delay)1
Functional Description
Each PLL block contains four programmable dividers as
shown in Figure 14 on page 16. These allow frequency
scaling of the input clock signal as follows:
• The n divider divides the input clock by integer factors
fro m 1 t o 32 .
• The m divider in the feedback path allows multiplication
of th e input clo c k by in te ge r factor s rang ing from 1 t o 6 4 .
• The t wo di vide rs t oge ther c an impl emen t any com bina tion
of mul t ip li c ati o n an d di v ision resu lt ing in a cl o ck
frequency between 24 and 180 MHz exiting the PLL core.
This clock has a fixed 50% duty cycle.
• The output freq uenc y of the PLL core is gi ven by the
following formula (fREF is the reference clock frequency):
fOUT = fREF * m/n
• The third and fourth dividers (u and v) permit the signals
appl ied to th e gl oba l n etw ork to eac h be fu rth er div ided b y
in teger factors ranging from 1 to 4.
The implementations:
fGLB = m/(n*u)
fGLA = m/(n*v)
enable the user to define a wide range of frequency
multipliers and divisors. The clock conditioning cir cuit can
advance or delay the clock up to 8 ns (in increments of
0.25ns) relative to the positive edge of the incoming
reference clock. The syst em also allow s for the selection of
output frequency clock phases of 0°, 90°, 180°, and 270°.
Prior to the application of signals to the rib drivers, they
pass through programmable delay units, one per global
network. These units permit the delaying of global signals
relative to other signals to assist in the control of input
set-up times. Not all possible combinations of input and
output modes can be used. The degrees of fre edom available
in the bidirectional global pad system and in the clock
conditioning circuit have been restricted. This avoids
unnecessary and unwieldy design kit and software work.
1. This mode is available through the delay feature of the Global MUX driver.