AD8331ARQ-REEL Analog Devices Inc, AD8331ARQ-REEL Datasheet - Page 48

• Manufacturer Part Number: AD8331ARQ-REEL
• Description: IC VGA SINGLE W/PREAMP 20-SSOP
• Manufacturer: Analog Devices Inc
• Series: X-AMP®r
• Type: Variable Gain Amplifierr

Specifications of AD8331ARQ-REEL

• Rohs Status: RoHS non-compliant
• Design Resources: Interfacing the High Frequency AD8331 to AD9215 (CN0096)
• Applications: Signal Processing
• Mounting Type: Surface Mount
• Package / Case: 20-QSOP
• For Use With: AD8331-EVALZ - BOARD EVAL FOR AD8331

AD8331/AD8332/AD8334
CONFIGURING THE INPUT IMPEDANCE
The board is built and tested using the components shown in
black in Figure 115. Provisions are made for optional components
(shown in gray) that can be installed at user discretion. As
shipped, the input impedances of the low noise amplifiers (LNAs)
are configured for 50 Ω to match the output impedances of most
signal generators and network analyzers. Input impedances up to
6 kΩ can be realized by changing the values of the feedback
resistors, R
and C12. For reference, Table 12 lists standard values of 1%
resistors for some typical values of input impedance. Of course,
if the user has determined that the source impedance falls
between these values, the feedback resistor value can be
calculated accordingly. Note that the board is designed to accept
standard surface-mount, size 0603 components.
Table 12. LNA External Component Values for Common
Source Impedances
R
50
75
100
200
500
6 k
Driving the VGA from an External Source or Using the
LNA to Drive an External Load
Appropriate components can be installed if the user wants to
drive the VGA directly from an external source or to evaluate
the LNA output. If the LNA is used to drive off-board loads
or cables, small value series resistors (47 Ω to 100 Ω) are
recommended for LNA decoupling. These can be installed
in the R10, R11, R14, R15, R18, R19, R22, and R23 spaces.
Provisions are made for surface-mount SMA connectors that
can be used for driving from either direction. If the LNA is not
used, it is recommended that the capacitors, C16, C17, C21,
C22, C26, C27, C31, and C32, be carefully removed to avoid
driving the outputs of the LNAs.
Using the Clamp Circuit
The board is shipped with no resistors installed in the spaces
provided for clamp-circuit operation. Note that each pair of
channels shares a clamp resistor. If the output clamping is
desired, the resistors are installed in R49 and R50. The peak-to-
peak clamping level is application dependent.
IN
(Ω)
RFB1, RFB2, RFB3, RFB4 (Ω, ±1%)
274
412
562
1.13 k
3.01 k
No resistor
FB1
, R
FB2,
R
FB3
, R
FB4
, and shunt capacitors, C6, C8, C10,
C6, C8, C10, C12 (pF)
22
12
8
1.2
No capacitor
No capacitor
Rev. G | Page 48 of 56
Viewing Signals
The preferred signal detector is a high impedance differential
probe, such as the Tektronix P6247, 1 GHz differential probe,
connected to the 2-pin headers (VO1, VO2, VO3, or VO4), as
shown in Figure 116. The low capacitance of this probe has the
least effect on the performance of the device of any detection
method tried. The probe can also be used for monitoring input
signals at IN1, IN2, IN3, or IN4. It can be used for probing
other circuit nodes; however, be aware that the 200 kΩ input
impedance can affect certain circuits.
Differential-to-single-ended transformers are provided for
single-ended output connections. Note that series resistors are
provided to protect against accidental output overload should a
50 Ω load be connected to the connector. Of course, the effect
of these resistors is to limit the bandwidth. If the load connected
to the SMA is >500 Ω, the 237 Ω series resistors, RX1, RX2, RX3,
RX4, RX5, RX6, RX7, and RX8, can be replaced with 0 Ω values.
MEASUREMENT SETUP
The basic board connections for measuring bandwidth are
shown in Figure 116. A 5 V, 200 mA (minimum) power supply
is required, and a low noise voltage reference supply is required
for VGAIN.
BOARD LAYOUT
The evaluation board circuitry uses four conductor layers. The
two inner layers are ground, and all interconnecting circuitry is
located on the outer layers. Figure 117 to Figure 120 illustrate
the copper patterns.
Figure 114. AD8334-EVALZ Assembly