AD9910/PCBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'AD9910/PCBZ' PDF : 60 Pages View PDF
SYNCHRONIZATION OF MULTIPLE DEVICES
The internal clocks of the AD9910 provide the timing for the
propagation of data along the baseband signal processing path.
These internal clocks are derived from the internal system clock
(SYSCLK) and are all submultiples of the SYSCLK frequency.
The logic state of all of these clocks in aggregate during any
given SYSCLK cycle defines a unique clock state. The clock state
advances with each cycle of SYSCLK, but the sequence of clock
states is periodic. By definition, multiple devices are synchronized
when their clock states match and they transition between states
simultaneously. Clock synchronization allows the user to asyn-
chronously program multiple devices but synchronously activate
the programming by applying a coincident I/O update to all
devices. It also allows multiple devices to operate in unison when
the parallel port is in use with either the QDUC or interpolating
DAC mode (see Figure 52).
The function of the synchronization logic in the AD9910 is to
force the internal clock generator to a predefined state coincident
with an external synchronization signal applied to the SYNC_IN
pins. If all devices are forced to the same clock state in synchro-
nization with the same external signal, then the devices are, by
definition, synchronized. Figure 49 is a block diagram of the
synchronization function. The synchronization logic is divided
into two independent blocks; a sync generator and a sync receiver,
both of which use the local SYSCLK signal for internal timing.
REF_CLK
SYSCLK INPUT
CIRCUITRY
90
REF_CLK
91
5
SYNC
GENERATOR
9
SYNC_OUT
10
SYNC
RECEIVER
ENABLE
SYNC
RECEIVER
DELAY
5
INTERNAL
CLOCKS
INPUT DELAY
AND EDGE
DETECTION
SYNC
RECEIVER
SETUP AND
HOLD VALIDATION
7
SYNC_IN
8
12 SYNC_SMP_ERR
6
4
SYNC STATE
SYNC
SYNC
PRESET VALUE VALIDATION TIMING
DELAY VALIDATION
DISABLE
Figure 49. Synchronization Circuit Block Diagram
AD9910
The synchronization mechanism relies on the premise that the
REFCLK signal appearing at each device is edge aligned with all
others as a result of the external REFCLK distribution system
(see Figure 52).
The sync generator block is shown in Figure 50. It is activated
via the sync generator enable bit. It allows for one AD9910 in a
group to function as a master timing source with the remaining
devices slaved to the master.
SYSCLK
÷16
÷N
DQ
PROGAMMABLE
DELAY
9
SYNC_OUT
1100
0
5
1
R
SYNC
GENERATOR
SYNC
POLARITY
DELAY
SYNC
GENERATOR
ENABLE
LVDS
DRIVER
Figure 50. Sync Generator Diagram
The sync generator produces a clock signal that appears at the
SYNC_OUT pins. This clock is delivered by an LVDS driver
and exhibits a 50% duty cycle. The clock has a fixed frequency
given by
fSYNC _ OUT
=
f SYSCLK
16
The clock at the SYNC_OUT pins synchronizes with either the
rising or falling edge of the internal SYSCLK signal as deter-
mined by the sync generator polarity bit. Because the SYNC_OUT
signal is synchronized with the internal SYSCLK of the master
device, the master device SYSCLK serves as the reference timing
source for all slave devices. The user can adjust the output delay
of the SYNC_OUT signal in steps of ~150 ps by programming
the 5-bit sync generator delay word via the serial I/O port. The
programmable output delay facilitates added edge timing
flexibility to the overall synchronization mechanism.
The sync receiver block (shown in Figure 51) is activated via the
sync receiver enable bit. The sync receiver consists of three sub-
sections; the input delay and edge detection block, the internal
clock generator block, and the setup and hold validation block.
The clock generator block remains operational even if the sync
receiver is not enabled.
Rev. 0 | Page 43 of 60
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