Datasheet

AD8331/AD8332/AD8334
Rev. G | Page 43 of 56
AD8332 EVALUATION BOARD
GENERAL DESCRIPTION
The AD8332-EVALZ is a platform for the testing and evaluation of
the AD8332 variable gain amplifier (VGA). The board is shipped
assembled and tested, and users need only connect the signal
and VGAIN sources to a single 5 V power supply. Figure 104 is a
photograph of the component side of the board, and Figure 105
shows the schematic. The AD8332-EVALZ is lead free and
RoHS compliant.
03199-131
Figure 104.Photograph of the AD8332-EVALZ
USER-SUPPLIED OPTIONAL COMPONENTS
The board is built and tested using the components shown in
black in Figure 105. Provisions are made for optional components
(shown in gray) that can be installed for testing at user discretion.
The default LNA input impedance is 50 Ω to match various
signal generators and network analyzers. Input impedances up to
6 kΩ are realized by changing the values of RFBx and CSHx. For
reference, Table 11 lists the common input impedance values
and corresponding adjustments. The board is designed for 0603
size, surface-mount components.
Table 11. LNA External Component Values for Common
Source Impedances
R
IN
(Ω) RFB1, RFB2 (Ω Std 1% Value) CSH1, CSH2 (pF)
50 274 22
75 412 12
100 562 8
200 1.13 k 1.2
500 3.01 k None
6 k
∞
None
SMA connectors, S2, S3, S6, and S7, are provided for access to
the LNA outputs or the VGA inputs. If the LNA is used alone,
0.1 µF coupling capacitors can be installed at the C5, C9, C23,
and C24 locations. Resistors of 68 Ω to 100 Ω may be required
if the load capacitances, as seen by the LNA outputs, are larger
than approximately 10 pF.
A resistor can be inserted at RCLMP if output clamping is desired.
The peak-to-peak clamping level is adjusted by installing one of
the standard 1% resistor values listed in Table 8.
A high frequency differential probe connected to the 2-pin headers,
VOx, is the preferred method to observe a waveform at the VGA
output. A typical setup is shown in Figure 106. Single-ended loads
can be connected directly via the board edge SMA connectors.
Note that the AD8332 output amplifier is buffered with 237 Ω
resistors; therefore, be sure to compensate for attenuation if low
impedances are connected to the output SMAs.
MEASUREMENT SETUP
The basic board connections for measuring bandwidth are
shown in Figure 106. A 5 V, 100 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 power and ground planes, and all
interconnecting circuitry is located on the outer layers. Figure 108
to Figure 111 illustrate the copper patterns.