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ADV7190/ADV7191

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APPENDIX 1

BOARD DESIGN AND LAYOUT CONSIDERATIONS

The ADV7190/ADV7191 is a highly integrated circuit contain-

ing both precision analog and high-speed digital circuitry. It

has been designed to minimize interference effects on the integ-

rity of the analog circuitry by the high-speed digital circuitry. It

is imperative that these same design and layout techniques be

applied to the system-level design such that high-speed, accurate

performance is achieved. The Recommended Analog Circuit Lay-

out shows the analog interface between the device and monitor.

The layout should be optimized for lowest noise on the ADV7190/

ADV7191 power and ground lines by shielding the digital inputs

and providing good decoupling. The lead length between groups

of VAA and GND pins should by minimized in order to mini-

mize inductive ringing.

Ground Planes

The ground plane should encompass all ADV7190/ADV7191

ground pins, voltage reference circuitry, power supply bypass cir-

cuitry for the ADV7190/ADV7191 , the analog output traces, and

all the digital signal traces leading up to the ADV7190/ADV7191.

This should be as substantial as possible to maximize heat spread-

ing and power dissipation on the board.

Power Planes

The ADV7190/ADV7191 and any associated analog circuitry

should have its own power plane, referred to as the analog power

plane (VAA). This power plane should be connected to the

regular PCB power plane (VCC) at a single point through a

ferrite bead. This bead should be located within three inches

of the ADV7190/ADV7191.

The metallization gap separating device power plane and board

power plane should be as narrow as possible to minimize the

obstruction to the flow of heat from the device into the general

board.

The PCB power plane should provide power to all digital logic

on the PC board, and the analog power plane should provide

power to all ADV7190/ADV7191 power pins and voltage reference

circuitry.

Plane-to-plane noise coupling can be reduced by ensuring that

portions of the regular PCB power and ground planes do not

overlay portions of the analog power plane, unless they can be

arranged so the plane-to-plane noise is common-mode.

Supply Decoupling

For optimum performance, bypass capacitors should be installed

using the shortest leads possible, consistent with reliable operation,

to reduce the lead inductance. Best performance is obtained

with 0.1

µF ceramic capacitor decoupling. Each group of V

pins on the ADV7190/ADV7191 must have at least one 0.1

µF

decoupling capacitor to GND. These capacitors should be placed

as close as possible to the device.

It is important to note that while the ADV7190/ADV7191

contains circuitry to reject power supply noise, this rejection

decreases with frequency. If a high-frequency switching power

supply is used, the designer should pay close attention to reducing

power supply noise and consider using a three-terminal voltage

regulator for supplying power to the analog power plane.

Digital Signal Interconnect

The digital inputs to the ADV7190/ADV7191 should be isolated

as much as possible from the analog outputs and other analog

circuitry. Also, these input signals should not overlay the ana-

log power plane.

Due to the high clock rates involved, long clock lines to the

ADV7190/ADV7191 should be avoided to reduce noise pickup.

Any active termination resistors for the digital inputs should be

connected to the regular PCB power plane (VCC), and not the

analog power plane.

Analog Signal Interconnect

The ADV7190/ADV7191 should be located as close as possible

to the output connectors to minimize noise pickup and reflec-

tions due to impedance mismatch.

The video output signals should overlay the ground plane, and

not the analog power plane, to maximize the high frequency power

supply rejection.

Digital inputs, especially pixel data inputs and clocking signals

should never overlay any of the analog signal circuitry and should

be kept as far away as possible.

For best performance, the outputs should each have a 300

Ω load

resistor connected to GND. These resistors should be placed as

close as possible to the ADV7190/ADV7191 so as to minimize

reflections.

The ADV7190/ADV7191 should have no inputs left floating.

Any inputs that are not required should be tied to ground.

ADV7191 Datasheet(PDF) 44 Page - Analog Devices

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