AD8051/AD8052/AD8054
noise bandwidth of the analog signal before analog-to-digital
conversion.
LAYOUT CONSIDERATIONS
The specified high speed performance of the AD8051/AD8052/
AD8054 requires careful attention to board layout and component
selection. Proper RF design techniques and low parasitic
component selection are necessary.
Note that the unused amplifier’s inputs should be tied to ground.
R6
1kΩ
C1
50pF
The PCB should have a ground plane covering all unused
portions of the component side of the board to provide a low
impedance path. The ground plane should be removed from the
area near the input pins to reduce parasitic capacitance.
R2
2kΩ
13
12
R4
2kΩ
C2
50pF
14
R1
3kΩ
R3
2
3
V
IN
R5
2kΩ
2kΩ
1
6
5
7
9
8
Chip capacitors should be used for supply bypassing. One end
should be connected to the ground plane and the other within
3 mm of each power pin. An additional large (4.7 μF to 10 μF)
tantalum electrolytic capacitor should be connected in parallel,
but not necessarily so close, to supply current for fast, large
signal changes at the output.
AD8054
10
AD8054
AD8054
BAND-PASS
FILTER OUTPUT
Figure 46. 2 MHz Biquad Band-Pass Filter Using AD8054
The frequency response of the circuit is shown in Figure 47.
0
The feedback resistor should be located close to the inverting
input pin to keep the parasitic capacitance at this node to a
minimum. Parasitic capacitance of less than 1 pF at the inverting
input can significantly affect high speed performance.
–10
–20
–30
–40
Stripline design techniques should be used for long signal traces
(greater than about 25 mm). These should be designed with a
characteristic impedance of 50 Ω or 75 Ω and be properly
terminated at each end.
ACTIVE FILTERS
Active filters at higher frequencies require wider bandwidth op
amps to work effectively. Excessive phase shift produced by
lower frequency op amps can significantly affect active filter
performance.
10k
100k
1M
10M
100M
FREQUENCY (Hz)
Figure 47. Frequency Response of 2 MHz Band-Pass Biquad Filter
Figure 46 shows an example of a 2 MHz biquad bandwidth filter
that uses three op amps of an AD8054. Such circuits are
sometimes used in medical ultrasound systems to lower the
Rev. H | Page 18 of 24
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