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4 Board Layout

5 Measurement Tips

Board Layout

This demonstration fixture is a four-layer PCB. The ground plane has been opened up around op amp

pins that are sensitive to capacitive loading. Power-supply traces are laid out to keep current loop areas to

a minimum. The SMA (or SMB) connectors may be mounted either vertically or horizontally onto the board

edge. The location and type of capacitors used for power-supply bypassing are crucial to high-frequency

amplifiers. The tantalum capacitors, C

and C

, do not need to be as close to pins 3 and 8 on the PCB

and may be shared with other amplifiers. See the individual op amp data sheets for more information on

proper board layout techniques and component selection.

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

environment; most data sheet plots are obtained under these conditions. It is easy to change the

component values for different input and output impedance levels. However, do not use high-impedance

probes; they represent a heavy capacitive load to the operational amplifier, 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.

SBOU040 – September 2006 DEM-OPA-MSOP-2B Demonstration Fixture 5

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