Data Sheet
AD9517-1
Rev. E | Page 47 of 80
Calculating the Fine Delay
The following values and equations are used to calculate the
delay of the delay block.
IRAMP (A) = 200 × (Ramp Current + 1)
Number of Capacitors = Number of Bits =
0 in Ramp Capacitors + 1
Example: 101 = 1 + 1 = 2; 110 = 1 + 1 = 2; 100 = 2 + 1 = 3;
001 = 2 + 1 = 3; 111 = 0 + 1 = 1.
Delay Range (ns) = 200 × ((No. of Caps + 3)/(IRAMP)) × 1.3286
( )
(
)
6
1
10
1600
0.34
ns
4
×
+
×
+
=
RAMP
I
Caps
of
No.
I
Offset
Delay Full Scale (ns) = Delay Range + Offset
Fine Delay (ns) =
Delay Range × Delay Fraction × (1/63) + Offset
Note that only delay fraction values up to 47 decimal (101111b;
0x2F) are supported.
In no case can the fine delay exceed one-half of the output clock
period. If a delay longer than half of the clock period is attempted,
the output stops clocking.
The delay function adds some jitter that is greater than that
specified for the nondelayed output. This means that the delay
function should be used primarily for clocking digital chips,
such as FPGA, ASIC, DUC, and DDC. An output with this delay
enabled may not be suitable for clocking data converters. The
jitter is higher for long full scales because the delay block uses
a ramp and trip points to create the variable delay. A slower
ramp time produces more time jitter.
Synchronizing the Outputs—Sync Function
Th
e AD9517 clock outputs can be synchronized to each other.
Outputs can be individually excluded from synchronization.
Synchronization consists of setting the nonexcluded outputs to
a preset set of static conditions and subsequently releasing these
outputs to continue clocking at the same instant with the preset
conditions applied. This allows for the alignment of the edges of
two or more outputs or for the spacing of edges according to the
coarse phase offset settings for two or more outputs.
Synchronization of the outputs is executed in several ways,
as follows:
By forcing the SYNC pin low and then releasing it (manual
sync).
By setting and then resetting any one of the following three
bits: the soft sync bit (Register 0x230[0]), the soft reset bit
(Register 0x000[2] [mirrored]), and the power-down
distribution reference bit (Register 0x230[1]).
By executing synchronization of the outputs as part of the
chip power-up sequence.
By forcing the RESET pin low and then releasing it (chip
reset).
By forcing the PD pin low and then releasing it (chip power-
down).
Following completion of a VCO calibration. An internal
SYNC signal is automatically asserted at the beginning of
a VCO calibration and then released upon its completion.
The most common way to execute the sync function is to use
the SYNC pin to do a manual synchronization of the outputs. This
requires a low-going signal on the SYNC pin, which is held low
and then released when synchronization is desired. The timing
and
Figure 58 (VCO divider not used). There is an uncertainty
of up to one cycle of the clock at the input to the channel divider
due to the asynchronous nature of the SYNC signal with respect
to the clock edges inside the
AD9517. The delay from the SYNC
rising edge to the beginning of synchronized output clocking is
between 14 and 15 cycles of clock at the channel divider input,
plus either one cycle of the VCO divider input (see
Figure 57),
depending on whether the VCO divider is used. Cycles are
counted from the rising edge of the signal.
Another common way to execute the sync function is by setting
and resetting the soft sync bit at Register 0x230[0] (see
Table 53through
Table 62 for details). Both the setting and resetting
of the soft sync bit require an update all registers operation
(Register 0x232[0] = 1) to take effect.