Data Sheet

ADV3219/ADV3220

Rev. A | Page 17 of 18

APPLICATIONS INFORMATION

The ADV3219 and ADV3220 are high speed muxes that can be

used to switch video or RF signals. The low output impedance

of the ADV3219/ADV3220 allows the output environment to

be optimized for use in 75 Ω or 50 Ω systems by choosing the

appropriate series termination resistor. For composite video

applications, the ADV3220 (gain of +2) is typically used to

provide compensation for the loss of the output termination.

CIRCUIT LAYOUT

Use of proper high speed design techniques is important to

ensure optimum performance. Use a low inductance ground

plane for power supply bypassing and to provide high quality

return paths for the input and output signals. For best performance,

it is recommended that power supplies be bypassed with 0.1 μF

ceramic capacitors placed as close to the body of the device as

possible. To provide stored energy for lower frequency, high

current output driving, place 10 μF tantalum capacitors farther

from the device.

The input and output signal paths should be stripline or micro-

strip controlled impedance. Video systems typically use a 75 Ω

characteristic impedance, whereas RF systems typically use 50 Ω.

Various calculators are available to calculate the trace geometry

that is required to produce the proper characteristic impedance.

TERMINATION

For a controlled impedance situation, termination resistors are

required at the inputs and output of the device. Ensure that the

input termination is a shunt resistor to ground with a value

matching the characteristic impedance of the input trace. To

reduce reflections, place the input termination resistor as close

to the device input pin as possible. To minimize the input-to-

input crosstalk, it is important to use a low inductance shield

between input traces to isolate each input. Consideration of

ground current paths must be taken to minimize loop currents

in the shields to prevent them from providing a coupling medium

for crosstalk.

For proper matching, the output series termination resistor

should be the same value as the characteristic impedance of the

output trace and placed as close to the output of the device as

possible. This placement reduces the high frequency effect of

series parasitic inductance, which can affect gain flatness and

−3 dB bandwidth.

CAPACITIVE LOAD

A high frequency output generally has difficulty when driving

a capacitive load. The usual response is some peaking in the

frequency domain or some overshoot in the time domain. If

these effects become too large, oscillation can result.

The response of the device under various capacitive loads is

shown in Figure 4 to Figure 10 and in Figure 13. If a condition

arises wherein excessive load capacitance is encountered and

the overshoot is too great or the part oscillates, use a small series

resistor of a few tens of ohms to improve the performance.