ADA4841-1YRZ Analog Devices, ADA4841-1YRZ Datasheet - Page 18

• Manufacturer Part Number: ADA4841-1YRZ
• Manufacturer: Analog Devices

ADA4841-1
Capacitor selection is critical for optimal filter performance.
Capacitors with low temperature coefficients, such as NPO
ceramic capacitors, are good choices for filter elements. Figure 49
shows the filter response.
LAYOUT CONSIDERATIONS
To ensure optimal performance, careful and deliberate attention
must be paid to the board layout, signal routing, power supply
bypassing, and grounding.
GROUND PLANE
It is important to avoid ground in the areas under and around
the input and output of the ADA4841-1. Stray capacitance
created between the ground plane and the input and output
pads of a device are detrimental to a high speed amplifier’s
performance. Stray capacitance at the inverting input, along
with the amplifier’s input capacitance, lowers the phase margin
and can cause instability. Stray capacitance at the output creates
a pole in the feedback loop. This can reduce phase margin and
can cause the circuit to become unstable.
–10
–15
–20
–25
–30
–35
–40
–5
5
0
0.03
Figure 49. Filter Frequency Response
0.1
FREQUENCY (MHz)
1
10
Rev. A | Page 18 of 20
POWER SUPPLY BYPASSING
Power supply bypassing is a critical aspect in the performance
of the ADA4841-1. A parallel connection of capacitors from
each of the power supply pins to ground works best. A typical
connection is shown in Figure 48. Smaller value capacitors offer
better high frequency response where larger value electrolytics
offer better low frequency performance. Paralleling different
values and sizes of capacitors helps to ensure that the power
supply pins are provided a low ac impedance across a wide band
of frequencies. This is important for minimizing the coupling of
noise into the amplifier. This can be especially important when
the amplifier PSR is starting to roll off—the bypass capacitors
can help lessen the degradation in PSR performance.
Starting directly at the ADA4841-1 power supply pins, the
smallest value capacitor should be placed on the same side of
the board as the amplifier, and as close as possible to the
amplifier power supply pin. The ground end of the capacitor
should be connected directly to the ground plane. Keeping the
capacitors’ distance short but equal from the load is important
and can improve distortion performance. This process should
be repeated for the next largest value capacitor.
It is recommended that a 0.01 μF ceramic 0508 case be used.
The 0508 case size offers low series inductance and excellent
high frequency performance. A 10 μF electrolytic capacitor
should be placed in parallel with the 0.01 μF capacitor.
Depending on the circuit parameters, some enhancement to
performance can be realized by adding additional capacitors.
Each circuit is different and should be individually analyzed for
optimal performance.