AD9040A

REV. B

–8–

Layout Information

Preserving the accuracy and dynamic performance of the

AD9040A requires that designers pay special attention to the

layout of the printed circuit board.

Analog paths should be kept as short as possible and be properly

terminated to avoid reflections. The analog input and reference

voltage connections should be kept away from digital signal

paths; this reduces the amount of digital switching noise which

is capacitively coupled into the analog section. Digital signal

paths should also be kept short, and run lengths should be

matched to avoid propagation delay mismatch. The AD9040A

digital outputs should be buffered or latched close to the device

(<2 cm). This prevents load transients which may feedback into

the device.

In high speed circuits, layout of the ground is critical. A single,

low impedance ground plane on the component side of the

board is recommended. Power supplies should be capacitively

coupled to the ground plane with high quality chip capacitors to

reduce noise in the circuit. Multilayer boards allow designers to

lay out signal traces without interrupting the ground plane, and

provide low impedance ground planes. In systems with dedi-

cated analog and digital grounds, all grounds of the AD9040A

should be connected to the analog ground plane.

The power supplies of the AD9040A should be isolated from

the supplies used for external devices; this reduces the amount

of noise coupled into the ADC. The digital +5 volt connection

device. Sockets limit dynamic performance and are not recom-

mended for use with the AD9040A.

EVALUATION BOARD

The evaluation board for the AD9040A (AD9040A/PCB) pro-

vides an easy and flexible method for evaluating the ADC’s

performance without (or prior to) developing a user-specific

printed circuit board. The two-sided board includes a recon-

struction DAC and digital output interface, and uses the layout

and applications suggestions outlined above. It is available from

Analog Devices at nominal cost.

Generous space is provided near the analog input and digital

outputs to support additional signal processing components the

user may wish to add. This prototyping area includes through

holes with 100-mil centers to support a variety of component

additions.

Input/Output/Supply Information

Power supply, analog input, clock connections, and recon-

structed output (RC OUTPUT) are identified by labels on the

evaluation board. Operation of the evaluation board should

conform to the following characteristics:

Table I. Evaluation Board Characteristics

Parameter

Typical

Units

Supply Current

+5 V

250

mA

–5.2 V

300

mA

Impedance

51

Ω

Voltage Range

±1.0

V

CLOCK

Impedance

51

Ω

Frequency

40

MSPS

RC OUTPUT

Impedance

51

Ω

Voltage Range

0 V to –1 V

V

Analog Input

Analog input signals can be fed directly into the Device Under

a 51

Ω resistor.