
PRODUCT SPECIFICATION
FMS3110/3115/3120/3125
REV. 1.03 9/19/00
9
Timing Diagram
CLK
PIXEL DATA
& CONTROLS
OUTPUT
DataN
DataN+1
DataN+2
tPWL
tS
tH
50%
3%/FS
90%
10%
tD
tSET
tF
tR
tPWH
1/fS
Applications Discussion
Figure 5 illustrates a typical FMS3110/3115/3120/3125
interface circuit. In this example, an optional 1.2 Volt band-
gap reference is connected to the VREF output, overriding
the internal voltage reference source.
Grounding
It is important that the FMS3110/3115/3120/3125 power
supply is well-regulated and free of high-frequency noise.
Careful power supply decoupling will ensure the highest
quality video signals at the output of the circuit. The
FMS3110/3115/3120/3125 has separate analog and digital
circuits. To keep digital system noise from the D/A converter,
it is recommended that power supply voltages (VDD) come
from the system analog power source and all ground connec-
tions (GND) be made to the analog ground plane. Power supply
pins should be individually decoupled at the pin.
Printed Circuit Board Layout
Designing with high-performance mixed-signal circuits
demands printed circuits with ground planes. Overall system
performance is strongly inuenced by the board layout.
Capacitive coupling from digital to analog circuits may
result in poor D/A conversion. Consider the following sug-
gestions when doing the layout:
1.
Keep the critical analog traces (VREF, IREF, COMP,
IOS, IOR, IOG) as short as possible and as far as possi-
ble from all digital signals. The FMS3110/3115/3120/
3125 should be located near the board edge, close to the
analog output connectors.
2.
Power plane for the FMS3110/3115/3120/3125 should
be separate from that which supplies the digital cir-
cuitry. A single power plane should be used for all of the
VDD pins. If the power supply for the FMS3110/3115/
3120/3125 is the same as that of the system's digital cir-
cuitry, power to the FMS3110/3115/3120/3125 should
be decoupled with 0.1F and 0.01F capacitors and iso-
lated with a ferrite bead.
3.
The ground plane should be solid, not cross-hatched.
Connections to the ground plane should have very short
leads.
4.
If the digital power supply has a dedicated power plane
layer, it should not be placed under the FMS3110/3115/
3120/3125, the voltage reference, or the analog outputs.
Capacitive coupling of digital power supply noise from
this layer to the FMS3110/3115/3120/3125 and its
related analog circuitry can have an adverse effect on
performance.
5.
CLK should be handled carefully. Jitter and noise on
this clock will degrade performance. Terminate the
clock line carefully to eliminate overshoot and ringing.
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