adl5331 Analog Devices, Inc., adl5331 Datasheet - Page 10

• Manufacturer Part Number: adl5331
• Description: 1 Mhz To 1.2 Ghz Vga With 30 Db Gain Control Range
• Manufacturer: Analog Devices, Inc.

ADL5331
APPLICATIONS INFORMATION
BASIC CONNECTIONS
Figure 15 shows the basic connections for operating the
ADL5331. There are two positive supplies, VPS1 and VPS2,
which must be connected to the same potential. Connect COM1
and COM2 (common pins) to a low impedance ground plane.
Apply a power supply voltage between 4.75 V and 5.25 V to
VPS1 and VPS2. Connect decoupling capacitors with 100 pF
and 0.1 μF power supplies close to each power supply pin. The
VPS2 pins (Pins 13 and Pin 18 through Pin 22) can share a pair
of decoupling capacitors because of their proximity to each other.
The outputs of the ADL5331, OPHI and OPLO, are open
collectors that need to be pulled up to the positive supply
with 120 nH RF chokes. The ac-coupling capacitors and
the RF chokes are the principle limitations for operation at
low frequencies. For example, to operate down to 1 MHz,
use 0.1 μF ac coupling capacitors and 1.5 μH RF chokes. Note
that in some circumstances, the use of substantially larger
inductor values results in oscillations.
Because the differential outputs are biased to the positive
supply, ac-coupling capacitors (preferably 100 pF) are needed
between the ADL5331 outputs and the next stage in the system.
Similarly, the INHI and INLO input pins are at bias voltages of
about 3.3 V above ground.
The nominal input and output impedance looking into each
individual RF input/output pin is 25 Ω. Consequently, the
differential impedance is 50 Ω.
VPOS
VPOS
GAIN
RFIN
0.1µF
0.1µF
C15
C12
100pF
10nF
10nF
100pF
C13
C14
C16
C11
Figure 15. Basic Connections
VPS1
COM1
INHI
INLO
COM1
VPS1
C10
10nF
Rev. 0 | Page 10 of 16
VPOS
ADL5331
C9
10nF
C1
0.1µF
C2
100pF
To enable the ADL5331, the ENBL pin must be pulled high.
Taking ENBL low puts the ADL5331 in sleep mode, reducing
current consumption to 250 μA at an ambient temperature.
The voltage on ENBL must be greater than 1.7 V to enable the
device. When enabled, the device draws 100 mA at low gain to
215 mA at maximum gain.
The ADL5331 is primarily designed for differential signals;
however, there are several configurations that can be imple-
mented to interface the ADL5331 to single-ended applications.
Figure 16 and Figure 17 show options for differential-to-single-
ended interfaces. Both configurations use ac-coupling capacitors
at the input/output and RF chokes at the output.
Figure 16 illustrates differential balance at the input and output
using a transformer balun. Input and output baluns are recom-
mended for optimal performance. Much of the characterization
for the ADL5331 was completed using 1:1 baluns at the input
and output for a single-ended 50 Ω match. Operation using
M/A-COM ETC1-1-13 transmission line transformer baluns
is recommended for a broadband interface; however, narrow-
band baluns can be used for applications requiring lower
insertion loss over smaller bandwidths.
COM2
COM2
OPLO
VPS2
VPS2
OPHI
RFIN
ETC1-1-13
VPOS
Figure 16. Differential Operation with Balun Transformers
L1
0.68µH L2
C7
100pF
C8
0.1µF
VPOS
10nF
10nF
10nF
10nF
0.68µH
C5
C6
C3
0.1µF
C4
100pF
INHI
INLO
RFOUT
ADL5331
RF VGA
OPLO
OPHI
120nH
+5V
120nH
10nF
10nF
ETC1-1-13
RFOUT