AD9547/PCBZ Analog Devices Inc, AD9547/PCBZ Datasheet - Page 40

• Manufacturer Part Number: AD9547/PCBZ
• Description: Clock Generator/Synchronizer Evaluation Board
• Manufacturer: Analog Devices Inc

Specifications of AD9547/PCBZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: Network Clock Generator/Synchronizer
• Kit Application Type: Clock & Timing
• Silicon Core Number: AD9547
• Main Purpose: Timing, Clock Generator
• Embedded: No
• Utilized Ic / Part: AD9547
• Primary Attributes: 2 Differential or 4 Single Ended Inputs
• Secondary Attributes: CMOS, LVPECL & LVDS Compatible
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9547
CLOCK DISTRIBUTION
The clock distribution block of the AD9547 provides an integrated
solution for generating multiple clock outputs based on frequency
dividing the DPLL output. The distribution output consists of
two channels (OUT0 and OUT1). Each channel has a dedicated
divider and output driver section, as shown in Figure 45.
Clock Input (CLKINx)
The clock input handles input signals from a variety of logic
families (assuming proper terminations and sufficient voltage
swing). It also handles sine wave input signals such as those
delivered by the DAC reconstruction filter. Its default operating
frequency range is 62.5 MHz to 500 MHz.
Super-Nyquist Operation
Typically, the maximum usable frequency at the DAC output is
about 45% of the system clock frequency. However, because it is
a sampled DAC, its output spectrum contains Nyquist images.
Of particular interest are the images appearing in the first Nyquist
zone (50% to 100% of the system clock frequency). Super-Nyquist
operation takes advantage of these higher frequencies, but this
implies that the CLKINx input operates in excess of 500 MHz,
which is outside its default operating limits.
The CLKINx receiver actually consists of two separate receivers:
the default receiver and an optional high frequency receiver,
which handles input signals up to 800 MHz. To select the high
frequency receiver, write a Logic 1 to Register 0x0400, Bit4.
Super-Nyquist operation requires a band-pass filter at the DAC
output instead of the usual low-pass reconstruction filter. Super-
Nyquist operation is viable as long as the image frequency does
not exceed the 800 MHz input range of the receiver. Furthermore,
to provide acceptable jitter performance, which is a consideration
for image signals with low amplitude, the signal at the CLKINx
inputs must meet the minimum slew rate requirements.
CONTROL
4
SYNC
Figure 45. Clock Distribution
Q0
4
OUT0
OUT1
ENABLE
SYNC SOURCE
4
n
/MODE
n
OUT0P
OUT0N
CLKINP
CLKINN
OUT_RSET
OUT1P
OUT1N
Rev. B | Page 40 of 104
Clock Dividers
The output clock distribution dividers are referred to as Q0 and Q1,
corresponding to the OUT0 and OUT1 output channels, respec-
tively. Each divider is programmable with 30 bits of division depth.
The actual divide ratio is one more than the programmed register
value; therefore, a register value of 3, for example, results in a
divide ratio of 4. Thus, each divider offers a range of divide ratios
from 1 to 2
With an even divide ratio, the output signal always exhibits a
50% duty cycle. When the clock divider is bypassed (a divide
ratio of 1), the output duty cycle is the same as the input duty
cycle. Odd output divide ratios (excluding 1) exhibit automatic
duty cycle correction given by
where:
N (which must be an odd number) is the divide ratio.
X is the normalized fraction of the high portion of the input period
(that is, 0 < X < 1).
For example, if N = 5 and the input duty cycle is 20% (X = 0.2),
then the output duty cycle is 44%. Note that, when the user
programs an output as noninverting, then the device adjusts the
falling edge timing to accomplish the duty cycle cor-rection.
Conversely, the device adjusts the rising edge timing for an
inverted output.
Output Power-Down
Each output channel offers independent control of power-down
functionality via the distribution settings register (Address 0x0400).
Each output channel has a dedicated power-down bit for powering
down the output driver. However, if both channels are powered
down, the entire distribution output enters a deep sleep mode.
Even though each channel has a channel power-down control
signal, it may sometimes be desirable to power down an output
driver while maintaining the divider’s synchronization with the
other channel dividers. This is accomplished by either of the
following methods:
•
•
Output Enable
Each output channel offers independent control of enable/
disable functionality using the distribution enable register
(Address 0x0401). The distribution outputs use synchronization
logic to control enable/disable activity to avoid the production
of runt pulses and to ensure that outputs with the same divide
ratios become active/inactive in unison.
In CMOS mode, use the divider output enable control bit
to stall an output. This provides power savings while main-
taining dc drive at the output.
In LVDS/LVPECL mode, place the output in tristate mode
(this works in CMOS mode as well).
Output
30
Duty
(1 to 1,073,741,824).
Cycle
=
N
+
2
2 −
N
X
1