lmh6629sdx National Semiconductor Corporation, lmh6629sdx Datasheet - Page 19

• Manufacturer Part Number: lmh6629sdx
• Description: Lmh6629 Ultra-low Noise, High Speed Operational Amplifier
• Manufacturer: National Semiconductor Corporation

LAYOUT CONSIDERATIONS
National Semiconductor suggests the copper patterns on the
evaluation board(s) for this product. These board(s) are also
useful as an aid in device testing and characterization. As is
the case with all high-speed amplifiers, accepted-practice RF
design technique on the PCB layout is mandatory. Generally,
a good high frequency layout exhibits a separation of power
supply and ground traces from the inverting input and output
pins. Parasitic capacitances between these nodes and
ground may cause frequency response peaking and possible
FIGURE 19. Equalizer Frequency Response
FIGURE 18. Low-Noise Magnetic Media Equalizer
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circuit oscillations (see Application Note OA-15 for more in-
formation). Use high-quality chip capacitors with values in the
range of 1000 pF to 0.1F for power supply bypassing. One
terminal of each chip capacitor is connected to the ground
plane and the other terminal is connected to a point that is as
close as possible to each supply pin as allowed by the
manufacturer’s design rules. In addition, connect a tantalum
capacitor with a value between 4.7 μF and 10 μF in parallel
with the chip capacitor.
Signal lines connecting the feedback and gain resistors
should be as short as possible to minimize inductance and
microstrip line effect. Place input and output termination re-
sistors as close as possible to the input/output pins. Traces
greater than 1 inch in length should be impedance matched
to the corresponding load termination.
Symmetry between the positive and negative paths in the
layout of differential circuitry should be maintained to mini-
mize the imbalance of amplitude and phase of the differential
signal.
Component value selection is another important parameter in
working
Choosing external resistors that are large in value compared
to the value of other critical components will affect the closed
loop behavior of the stage because of the interaction of these
resistors with parasitic capacitances. These parasitic capac-
itors could either be inherent to the device or be a by-product
of the board layout and component placement. Moreover, a
large resistor will also add more thermal noise to the signal
path. Either way, keeping the resistor values low will diminish
this interaction. On the other hand, choosing very low value
resistors could load down nodes and will contribute to higher
overall power dissipation and high distortion.
with
high-speed/high-performance
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amplifiers.