adl5562 Analog Devices, Inc., adl5562 Datasheet - Page 16

• Manufacturer Part Number: adl5562
• Description: 3.3 Ghz Ultralow Distortion Rf/if Differential Amplifier
• Manufacturer: Analog Devices, Inc.

ADL5562
The single-ended gain can be determined using the following
formula below. The values of R
uration are shown in Table 7.
Table 7. Values of R
Gain (dB)
5.6
11.1
14.1
1
GAIN ADJUSTMENT AND INTERFACING
The effective gain of the ADL5562 can be reduced using a number
of techniques. A matched attenuator network can reduce the
effective gain, but this requires the addition of a separate com-
ponent that can be prohibitive in size and cost. Instead, a simple
voltage divider can be implemented using the combination of
additional series resistors at the amplifier input and the input
impedance of the ADL5562, as shown in Figure 36. A shunt
resistor is used to match to the impedance of the previous stage.
Figure 36 shows a typical implementation of the divider concept
that effectively reduces the gain by adding attenuation at the
input. For frequencies less than 100 MHz, the input impedance
of the ADL5562 can be modeled as a real 133 Ω, 200 Ω, or 400 Ω
resistance (differential) for maximum, middle, and minimum
gains, respectively. Assuming that the frequency is low enough
to ignore the shunt reactance of the input and high enough so
that the reactance of moderately sized ac-coupling capacitors
can be considered negligible, the insertion loss, Il, due to the
shunt divider can be expressed as
The necessary shunt component, R
impedance, R
The insertion loss and the resultant power gain for multiple
shunt resistor values are summarized in Table 8. The source
resistance and input impedance need careful attention when
using Equations 3 and 4. The reactance of the input impedance
These values based on a 50 Ω input match.
1
1
/
/
AC
A
2
2
Il
R
V
R
R
(
SHUNT
1
S
S
dB
=
)
R
Figure 36. Gain Adjustment Using a Series Resistor
N
=
=
1
1
S
+
, can be expressed as
/
/
20
2
2
⎛
⎜
⎜
⎝
R
R
R
400
1
R
R
SHUNT
SHUNT
log
s
S
S
×
+
−
IN
⎛
⎜ ⎜
⎝
R
R
2
R
R
2
and R
⎞
⎟
⎟
⎠
SERIES
SERIES
R
200
100
66.7
×
1
IN
0.1 µF
0.1µF
R
R
(Ω)
S
1
IN
R
X
+
+
2
+
IN
for Single-Ended Gain
1
1
R
/
/
R
2
2
2
R
and R
R
R
IN
×
IN
SERIES
SERIES
SHUNT
R
⎞
⎟ ⎟
⎠
X
R
+
X
X
, to match to the source
for each gain config-
R
S
×
VIN1
VIN2
VIP1
VIP2
10
R
R2 || 307
R2 || 179
R2 || 132
R
X
+
L
ADL5562
(Ω)
R
L
1
1
1
Rev. 0 | Page 16 of 24
(2)
(3)
(4)
AC
of the ADL5562 and the ac-coupling capacitors must be con-
sidered before assuming that they make a negligible contribution.
Table 8. Gain Adjustment Using Series Resistor
Il (dB)
2
4
2
4
2
2
4
2
4
2
4
2
ADC INTERFACING
The ADL5562 is a high output linearity amplifier that is opti-
mized for ADC interfacing. There are several options available
to the designer when using the ADL5562. Figure 37 shows a
simplified wideband interface with the ADL5562 driving a
AD9445. The AD9445 is a 14-bit, 125 MSPS ADC with a buf-
fered wideband input.
For optimum performance, the ADL5562 should be driven
differentially using an input balun. Figure 37 uses a wideband
1:1 transmission line balun followed by two 34.8 Ω resistors in
parallel with the three input impedances, which change with the
gain selection of the AD5562, to provide a 50 Ω differential
input impedance. This provides a wideband match to a 50 Ω
source. The ADL5562 is ac coupled from the AD9445 to avoid
common-mode dc loading. The 33 Ω series resistors help to
improve the isolation between the ADL5562 and any switching
currents present at the analog-to-digital sample and hold input
circuitry. The AD9445 input presents a 2 kΩ differential load
impedance and requires a 2 V p-p differential input swing to
reach full scale (VREF = 1 V).
This circuit provides variable gain, isolation, and source
matching for the AD9445. Using this circuit with the ADL5562
in a gain of 6 dB, an SFDR performance of 87 dBc is achieved at
140 MHz and a −3 dB bandwidth of 760 MHz, as indicated in
Figure 38 and Figure 39.
The wideband frequency response is an advantage in broad-
band applications such as predistortion receiver designs and
50Ω
Figure 37. Wideband ADC Interfacing Example Featuring the AD9445
ETC1-1-13
R
400
400
200
200
133
400
400
200
200
400
400
200
IN
34.8Ω
34.8Ω
(Ω)
0.1 µF
0.1µF
R
50
50
50
50
50
200
200
200
200
50
50
50
S
A
B
(Ω)
VIP2
VIP1
VIN1
VIN2
ADL5562
3.3V
R
105
232
51.1
115
34.8
102
232
51.1
115
105
232
51.1
SERIES
VON
VOP
(Ω)
0.1 µF
0.1µF
R
54.9
54.9
61.9
59
71.5
332
294
976
549
54.9
54.9
61.9
33Ω
33Ω
SHUNT
14-BIT ADC
AD9445
(Ω)
VIN+
VIN–
14