ad768-eb Analog Devices, Inc., ad768-eb Datasheet - Page 16

• Manufacturer Part Number: ad768-eb
• Description: 16-bit, 30 Msps D/a Converter
• Manufacturer: Analog Devices, Inc.

AD768
Clock Input
An external sample clock must be provided to either the BNC
connector labeled “CLOCK” or on Pin 33 of the IDC connec-
tor. This clock must comply with the logic levels outlined in the
AD768 data sheet. The “CLOCK” input is terminated with a
removable 51
is unterminated.
SW1. Clock source select switch. When SW1 is in position 1, Pin
33 of the IDC connected is applied to the CLOCK input of the
AD768. When SW2 is in position 2, the “CLOCK” BNC connec-
tor is applied to the CLOCK input of the AD768.
Digital Inputs
The digital inputs of the AD768, DB0–DB15, are available via
J1, a 40-pin IDC connector. These inputs should comply with
the specifications given in the AD768 data sheet.
Layout Considerations
Figures 28 and 29 show the AD768-EB ground and power
plane layouts. Figures 35–38 show the schematic diagram, trace
routing, silk screening, and component layout for the AD768 4
layer evaluation board.
Separate ground and power planes have several advantages for
high speed layouts. (For further information outlining these
advantages, see the application note “Design and Layout of a
Video Graphics System for Reduced EMI” [E1309] available
from Analog Devices [[phone]].) A solid ground plane
can be used if the digital return current can be routed such that
it does not modulate the analog ground plane. If this is not pos-
sible, it may be necessary to split the ground plane in order to
force currents to flow in a controlled direction. This type of
grounding scheme is shown in the Figure 28. The ground plane
is separated into analog and digital planes that are joined
together under the AD768. In any case, the AD768 should be
treated as an analog component and a common ground connec-
tion should be made underneath the AD768 despite some pins
being labeled “digital” ground and some as “analog” ground.
A complete parts list for the AD768 evaluation board is given in
Table IV.
resistor. The IDC connector clock connection
–16–
Reference
U1
U2
T1
A, B, CLOCK BNC JACKs,
JP1–5
SW1, 2
J1
R1
R2
R3, R13–21, &
R5
R7
R11
R12
C1–4
C5–8, C10, 12,
C9, 11, 13, 15 22 F Tant. Cap., Teardrop,
R23–29
14, & C16–19
Table III. Summary of Jumper Functionality
Installed
Jumper
JP1
JP2
JP3 (STBY)
JP4
JP5
Value / Part Type Package
AD768
AD811
Mini-Circuits
T4–6T
Small
Header
SPDT, Secme
40-Pin IDC
Connector
500
25
Wire Jumpers
500
100
51
10 k Pot.
1 F Ceram. Cap. Leaded
25 V
Table IV. AD768-EB Parts List
Jumper Function
Buffered Output A
50
Unbuffered Output A
Unbuffered Output B
Buffered Output B
28-Pin SOIC
8-Pin DIP
Not Installed
Small, Vertical
2-Pin
0.1"
R.A., Male,
w/ Latches
1/4 W, 0.01%,
Vishay
1/4 W, 0.01%,
Vishay
1/4 W, 0.01%,
Vishay
1/4 W, 0.01%,
Vishay
1/8 W, 5%, Carbon 1
3266 W
0.1 F Chip Cap,
1206
0.1" Spacing
Transformer Output
0.3"
Qty/Bd
1
1
3
5
2
1
1
1
17
1
1
1
4
11
1
4
REV. B