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4 Board Layout

5 Measurement Tips

Board Layout

This demonstration fixture is a four-layer PCB. Mid-layer 1 has only power traces. Mid-layer 2 has both

ground and power traces. The ground plane has been opened up around op amp pins sensitive to

capacitive loading. Power-supply traces are laid out to keep current loop areas to a minimum. Mount the

SMA (or SMB) connectors vertically. The location and type of capacitors used for power-supply bypassing

are crucial to high-frequency amplifiers. The tantalum capacitors, C

BYP

and C

BYP

, do not need to be

as close to pins 6 and 2 on the PCB, and may be shared with other amplifiers. See the individual op amp

data sheets for more information on component selection.

This demonstration fixture, and the component values shown, is designed to operate in a 50 Ω

environment. Most data sheet plots are obtained this way. It is easy to change the component values for

different input and output impedance levels. Do not use high impedance probes; they represent a heavy

capacitive load to the op amp, and will alter the amplifier response. Instead, use low impedance ( ≤ 500 Ω )

probes with adequate bandwidth. The probe input capacitance and resistance set an upper limit on the

measurement bandwidth. If a high impedance probe must be used, place a 100 Ω resistor on the probe tip

to isolate its capacitance from the circuit.

SBOU027B – October 2004 – Revised April 2006 DEM-OPA-SOT-1B User's Guide 3

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