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OPA2863

SBOS982A – JUNE 2020 – REVISED JUNE 2020

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10 Power Supply Recommendations

The OPAx863 devices are intended for operation on supplies ranging from 2.7 V to 12.6 V. The OPAx863

devices may operate on single-sided supplies, split and balanced bipolar supplies, or unbalanced bipolar

supplies. Operating from a single supply can have numerous advantages. With the negative supply at ground,

the DC errors due to the –PSRR term can be minimized. Typically, AC performance improves slightly at 10-V

operation with minimal increase in supply current. Minimize the distance (< 0.1 in) from the power supply pins to

high-frequency, 0.01-µF decoupling capacitors. A larger capacitor (2.2 µF typical) is used along with a high-

frequency, 0.01-µF supply-decoupling capacitor at the device supply pins. For single-supply operation, only the

positive supply has these capacitors. When a split-supply is used, use these capacitors from each supply to

ground. If necessary, place the larger capacitors further from the device and share these capacitors among

several devices in the same area of the printed circuit board (PCB). An optional supply decoupling capacitor

across the two power supplies (for split-supply operation) reduces second harmonic distortion.

11 Layout

11.1 Layout Guidelines

Achieving optimum performance with a high-frequency amplifier like the OPAx863 devices require careful

attention to board layout parasitics and external component types. The OPA2863EVM can be used as a

reference when designing the circuit board. Recommendations that optimize performance include:

1. Minimize parasitic capacitance to any AC ground for all of the signal I/O pins. Parasitic capacitance on the

output and inverting input pins can cause instability—on the noninverting input, it can react with the source

impedance to cause unintentional band-limiting. To reduce unwanted capacitance, open a window around

the signal I/O pins in all of the ground and power planes around those pins. Otherwise, ground and power

planes must be unbroken elsewhere on the board.

2. Minimize the distance (< 0.1 in) from the power-supply pins to high-frequency 0.01-µF decoupling

capacitors. At the device pins, do not allow the ground and power plane layout to be in close proximity to the

signal I/O pins. Avoid narrow power and ground traces to minimize inductance between the pins and the

decoupling capacitors. The power-supply connections must always be decoupled with these capacitors.

Larger (2.2-µF to 6.8-µF) decoupling capacitors, effective at lower frequency, must also be used on the

supply pins. These can be placed somewhat farther from the device and shared among several devices in

the same area of the PC board.

3. Careful selection and placement of external components preserve the high frequency performance of

the OPAx863 devices. Resistors must be a low reactance type. Surface-mount resistors work best and

allow a tighter overall layout. Metal film and carbon composition axially leaded resistors can also provide

good high frequency performance. Again, keep their leads and PCB trace length as short as possible. Never

use wirewound type resistors in a high frequency application. Because the output pin and inverting input pin

are the most sensitive to parasitic capacitance, always position the feedback and series output resistor, if

any, as close as possible to the output pin. Other network components, such as noninverting input

termination resistors, must also be placed close to the package. Even with a low parasitic capacitance

shunting the external resistors, excessively high resistor values can create significant time constants that can

degrade performance. Good axial metal film or surface mount resistors have approximately 0.2 pF in shunt

with the resistor. For resistor values > 10 kΩ, this parasitic capacitance can add a pole or zero close to the

GBWP of 50 MHz and subsequently affects circuit operation. Keep resistor values as low as possible

consistent with load driving considerations. Lowering the resistor values keep the resistor noise terms low,

and minimize the effect of its parasitic capacitance, however lower resistor values increase the dynamic

applications (see the Transimpedance Amplifier section) can use whatever feedback resistor is required by

the application as long as the feedback compensation capacitor is set considering all parasitic capacitance

terms on the inverting node.

4. Connections to other wideband devices on the board may be made with short direct traces or through

onboard transmission lines. For short connections, consider the trace and the input to the next device as a

lumped capacitive load. Relatively wide traces (50 mils to 100 mils) must be used, preferably with ground

devices are nominally compensated to operate with a 2.5-pF parasitic load. Higher parasitic capacitive loads