ADA4896-2 AD [Analog Devices], ADA4896-2 Datasheet - Page 24

• Manufacturer Part Number: ADA4896-2
• Description: 1 nV/?Hz, Low Power, Rail-to-Rail Output Amplifiers
• Manufacturer: AD [Analog Devices]

ADA4896-2/ADA4897-1
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 ADA4896-2/ADA4897-1. Stray
capacitance created between the ground plane and the input
and output pads of a device are detrimental to high speed
amplifier performance. Stray capacitance at the inverting
input, along with the amplifier 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.
POWER SUPPLY BYPASSING
Power supply bypassing is a critical aspect in the performance
of the ADA4896-2/ADA4897-1. A parallel connection of capac-
itors from each of the power supply pins to ground works best.
Smaller value capacitors offer better high frequency response,
whereas larger value electrolytics offer better low frequency
performance. Paralleling different values and sizes of capacitors
Figure 54. Using the
CHANNEL A
CHANNEL H
LNA
LNA
ADA4896-2/ADA4897-1
GENERATION
4
LO
as Filters, I-to-V Converters, Current Summers, and ADC Drivers After the I/Q Outputs of the
Φ
Φ
Φ
Φ
AD9279
Rev. 0 | Page 24 of 28
CWI+
CWI–
CWQ+
CWQ–
1.5V
1.5V
1.5V
1.5V
R
R
R
A
A
A
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
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
capacitor’s 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 0.1 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 0.1 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.
R
C
C
R
R
C
C
R
FILT
FILT
FILT
FILT
FILT
FILT
FILT
FILT
ADA4896-2/
ADA4897-1
ADA4896-2/
ADA4897-1
2.5V
2.5V
2.5V
2.5V
ADA4896-2/
ADA4897-1
ADA4896-2/
ADA4897-1
ADA4896-2/ADA4897-1
50Ω
50Ω
50Ω
50Ω
4nF
4nF
18-BIT ADC
18-BIT ADC
AD7982
AD7982
AD9279
power supply
Q
I