EP4CGX75DF27C7N Altera, EP4CGX75DF27C7N Datasheet - Page 94

• Manufacturer Part Number: EP4CGX75DF27C7N
• Description: Cyclone IV GX
• Manufacturer: Altera
• Series: CYCLONE® IV GXr

Specifications of EP4CGX75DF27C7N

• Number Of Logic Elements/cells: 73920
• Number Of Labs/clbs: 4620
• Total Ram Bits: 4257792
• Number Of I /o: 310
• Number Of Gates: -
• Voltage - Supply: 1.16 V ~ 1.24 V
• Mounting Type: *
• Operating Temperature: 0°C ~ 85°C
• Package / Case: *
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

5–32
Programmable Bandwidth
Phase Shift Implementation
Cyclone IV Device Handbook, Volume 1
Figure 5–20. VCO Switchover Operating Frequency
■
The PLL bandwidth is the measure of the PLL’s ability to track the input clock and its
associated jitter. PLLs of Cyclone IV devices provide advanced control of the PLL
bandwidth using the programmable characteristics of the PLL loop, including loop
filter and charge pump. The closed-loop gain 3-dB frequency in the PLL determines
the PLL bandwidth. The bandwidth is approximately the unity gain point for open
loop PLL response.
Phase shift is used to implement a robust solution for clock delays in Cyclone IV
devices. Phase shift is implemented with a combination of the VCO phase output and
the counter starting time. The VCO phase output and counter starting time are the
most accurate methods of inserting delays, because they are based only on counter
settings that are independent of process, voltage, and temperature.
You can phase shift the output clocks from the PLLs of Cyclone IV devices in one of
two ways:
■
■
Fine resolution phase shifts are implemented by allowing any of the output counters
(C[4..0]) or the M counter to use any of the eight phases of the VCO as the reference
clock. This allows you to adjust the delay time with a fine resolution.
Disable the system during switchover if the system is not tolerant to frequency
variations during the PLL resynchronization period. You can use the clkbad0
and clkbad1 status signals to turn off the PFD (pfdena = 0) so the VCO
maintains its last frequency. You can also use the switchover state machine to
switch over to the secondary clock. Upon enabling the PFD, output clock enable
signals (clkena) can disable clock outputs during the switchover and
resynchronization period. After the lock indication is stable, the system can
re-enable the output clock or clocks.
Fine resolution using VCO phase taps
Coarse resolution using counter starting time
F vco
Primary Clock Stops Running
Switchover Occurs
Chapter 5: Clock Networks and PLLs in Cyclone IV Devices
© December 2010 Altera Corporation
VCO Tracks Secondary Clock
Programmable Bandwidth
Frequency Overshoot