AD8331ARQZ-R7 datasheet(39/56 Pages) AD

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AD8331/AD8332/AD8334

Rev. G | Page 39 of 56

AD8331 EVALUATION BOARD

GENERAL DESCRIPTION

The AD8331 evaluation board is a platform for testing and

evaluating the AD8331 variable gain amplifier (VGA). The

board is provided completely assembled and tested; the user

simply connects an input signal, VGAIN sources, and a 5 V

power supply. The AD8331-EVALZ is lead free and RoHS

compliant. Figure 95 is a photograph of the board.

USER-SUPPLIED OPTIONAL COMPONENTS

As shown in the schematic in Figure 96, the board provides for

optional components. The components shown in black are for

typical operation, and the components shown in gray are

installed at the user’s discretion.

As shipped, the LNA input impedance of the AD8331-EVALZ is

configured for 50 Ω to accommodate most signal generators and

network analyzers. Input impedances up to 6 kΩ are realized by

changing the values of RFB and CSH. Refer to the Theory of

Operation section for details on this circuit feature. See Table 9

for typical values of input impedance and corresponding

components.

Figure 95. Photograph of AD8331-EVALZ

MEASUREMENT SETUP

The basic board connection for measuring bandwidth is shown

in Figure 97. A 5 V, 100 mA minimum power supply and a low

noise, voltage reference supply for GAIN are required. Table 10

lists jumpers, and Figure 97 shows their functions and positions.

Table 9. LNA External Component Values for Common

Source Impedances

The preferred signal detection method is a differential probe

connected to VO, as shown in Figure 97. Single-ended loads can be

connected using the board edge SMA connector, VOH. Be sure to

take into account the 25.8 dB attenuation incurred when using the

board in this manner. For connection to an ADC, the 270 Ω series

resistors can be replaced with 0 Ω or other appropriate values.

RIN (Ω)

RFB (Ω, Nearest 1% Value)

CSH (pF)

274

412

100

562

200

1.13 k

1.2

500

3.01 k

None

6 k

∞

None

Table 10. Jumper Functions

Switch

Function

LNA_EN

Enables the LNA when in the top position

VGA_EN

Enables the VGA when in the top position

W5, W6

Connects the AD8331 outputs to the SMA connectors

GN_SLOPE

Left = gain increases with VGAIN

Right = gain decreases with VGAIN

GN_HI_LO

Left = high gain

Right = LO gain

The board is designed for 0603 size, surface-mount components.

Back-to-back diodes can be installed at Location D3 if desired.

To evaluate the LNA as a standalone amplifier, install optional

SMA connectors LON and LOP and capacitors C1 and C2;

typical values are 0.1 μF or smaller. At R4 and R8, 0 Ω resistors

are installed unless capacitive loads larger than 10 pF are connected

to the SMA connectors LON and LOP (such as coaxial cables).

In that event, small value resistors (68 Ω to 100 Ω) must be

installed at R4 and R8 to preserve the stability of the amplifier.

BOARD LAYOUT

The evaluation board circuitry uses four conductor layers. The

two inner layers are grounded, and all interconnecting circuitry

is located on the outer layers. Figure 99 to Figure 102 illustrate

the copper patterns.

A resistor can be inserted at RCLMP if output clamping is

desired. Refer to Table 8 for appropriate values.

AD8331ARQZ-R7 数据表(PDF) 39 Page - Analog Devices

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