EP4CE30F29C7N Datasheet, PDF (88/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

5–26
Chapter 5: Clock Networks and PLLs in Cyclone IV Devices
Hardware Features
Deterministic Latency Compensation Mode
The deterministic latency mode compensates for the delay of the multipurpose PLLs
through the clock network and serializer in Common Public Radio Interface (CPRI)
applications. In this mode, the PLL PFD feedback path compensates the latency
uncertainty in Tx dataout and Tx clkout paths relative to the reference clock.
Hardware Features
Cyclone IV PLLs support several features for general-purpose clock management.
This section discusses clock multiplication and division implementation,
phase shifting implementations, and programmable duty cycles.
Clock Multiplication and Division
Each Cyclone IV PLL provides clock synthesis for PLL output ports using
M/(N*post-scale counter) scaling factors. The input clock is divided by a pre-scale
factor, N, and is then multiplied by the M feedback factor. The control loop drives the
VCO to match f_IN (M/N). Each output port has a unique post-scale counter that
divides down the high-frequency VCO. For multiple PLL outputs with different
frequencies, the VCO value is the least common multiple of the output frequencies
that meets its frequency specifications. For example, if output frequencies required
from one PLL are 33 and 66 MHz, the Quartus II software sets the VCO to 660 MHz
(the least common multiple of 33 and 66 MHz in the VCO range). Then, the post-scale
counters scale down the VCO frequency for each output port.
There is one pre-scale counter, N, and one multiply counter, M, per PLL, with a range
of 1 to 512 for both M and N. The N counter does not use duty cycle control because
the purpose of this counter is only to calculate frequency division. There are five
generic post-scale counters per PLL that can feed GCLKs or external clock outputs.
These post-scale counters range from 1 to 512 with a 50% duty cycle setting. The
post-scale counters range from 1 to 256 with any non-50% duty cycle setting. The sum
of the high/low count values chosen for a design selects the divide value for a given
counter.
The Quartus II software automatically chooses the appropriate scaling factors
according to the input frequency, multiplication, and division values entered into the
ALTPLL megafunction.
1 Phase alignment between output counters is determined using the t_{PLL_PSERR}
specification.
Cyclone IV Device Handbook,
Volume 1
October 2012 Altera Corporation