AD9927 Analog Devices, AD9927 Datasheet - Page 16

• Manufacturer Part Number: AD9927
• Description: 14-Bit CCD Signal Processor
• Manufacturer: Analog Devices

AD9927
HIGH SPEED PRECISION TIMING CORE
The AD9927 generates high speed timing signals using the
flexible Precision Timing core. This core is the foundation for
generating the timing used for both the CCD and the AFE; it
includes the reset gate RG, horizontal drivers H1 to H8, HL,
and SHP/SHD sample clocks. A unique architecture makes it
routine for the system designer to optimize image quality by
providing precise control over the horizontal CCD readout
and the AFE correlated double sampling.
The high speed timing of the AD9927 operates the same
way in either master or slave mode configuration. For more
information on synchronization and pipeline delays, see
the Power-Up Sequence for Master Mode section.
Timing Resolution
The Precision Timing core uses a 1× master clock input as a
reference (CLI). This clock should be the same as the CCD pixel
clock frequency. Figure 16 illustrates how the internal timing
core divides the master clock period into 64 steps or edge
positions. Using a 40 MHz CLI frequency, the edge resolution
of the Precision Timing core is approximately 0.4 ns. If a 1×
system clock is not available, it is possible to use a 2× reference
ONE PIXEL
POSITION
PERIOD
CLI
H1, H3, H5, H7
H2, H4, H6, H8
NOTES
1. THE PIXEL CLOCK PERIOD IS DIVIDED INTO 64 POSITIONS, PROVIDING FINE EDGE RESOLUTION FOR HIGH SPEED CLOCKS.
2. THERE IS A FIXED DELAY FROM THE CLI INPUT TO THE INTERNAL PIXEL PERIOD POSITION (t
t
CLIDLY
SIGNAL
CCD
RG
HL
3
5
7
PROGRAMMABLE CLOCK POSITIONS:
1
2
3
4
5
6
7
8
SHP SAMPLE LOCATION.
SHD SAMPLE LOCATION.
RG RISING EDGE.
RG FALLING EDGE.
H1 RISING EDGE.
H1 FALLING EDGE.
HL RISING EDGE.
HL FALLING EDGE.
P[0]
4
Figure 17. High Speed Clock Programmable Locations (HCLKMODE = 001)
Figure 16. High Speed Clock Resolution from CLI, Master Clock Input
1
6
8
P[16]
2
Rev. 0 | Page 16 of 100
P[32]
clock by programming the CLIDIVIDE register (AFE Register
Address 0x0D). The AD9927 then internally divides the CLI
frequency by 2.
The AD9927 includes a master clock output, CLO, which
is the inverse of CLI. This output should be used as a crystal
driver. A crystal can be placed between the CLI and CLO pins
to generate the master clock for the AD9927.
High Speed Clock Programmability
Figure 17 shows when the high speed clocks RG, H1 to H8,
SHP, and SHD are generated. The RG pulse has programmable
rising and falling edges and can be inverted using the polarity
control. Horizontal Clock H1 has programmable rising and
falling edges and polarity control. In HCLK Mode 1, H3, H5,
and H7 are equal to H1 and H2, H4, H6, and H8 are always
inverses of H1.
The edge location registers are each six bits wide, allowing the
selection of all 64 edge locations. Figure 20 shows the default
timing locations for all of the high speed clock signals.
P[48]
CLIDLY
).
P[64] = P[0]