REV. 0

AD8325

–10–

Differential Inputs

The AD8325-EVAL evaluation board may be driven with a

differential signal in one of two ways. A transformer may be

used to convert a single-ended signal to differential, or a differ-

ential signal source may be used. Figure 7 and the following

paragraphs describe each of these methods.

Single-Ended-to-Differential Input (Figure 7, Option 1)

A TOKO 617DB-A0070 1:1 transformer is preinstalled in the

T3 location of the evaluation board. Install 0

Ω chip resistors at

R14, R15, and R20, and leave R16 through R19 open. For

50

Ω differential input impedance, install a 51.1 Ω resistor at R13.

For 75

Ω differential input impedance, use a 78.7 Ω resistor.

In this configuration, the input signal must be applied to the

than 50

Ω or 75 Ω, the correct value for R13 can be calculated

using the following equation.

Desired Input Impedance = (R13 1600)

Differential Input (Figure 7, Option 2)

If a differential signal source is available, it may be applied

board. In this case, 0

Ω chip resistors should be installed at

locations R16 through R19, and R14, R15, and R20 should be

left open. The equation at the end of the preceding paragraph

can be used to compute the correct value for R13 for any

desired differential input impedance. For differential input

impedances of 75

Ω or 150 Ω, the value of R13 will be 78.7 Ω or

165

Ω respectively.

AD8325

DIFFERENTIAL INPUT, OPTION 2

R13

DIFF IN

T1

R13

AD8325

DIFFERENTIAL INPUT, OPTION 1

Figure 7. Differential Input Termination Options

Installing the Visual Basic Control Software

To install the “CABDRIVE_25” evaluation board control soft-

ware, close all Windows applications and then run “SETUP.EXE”

located on Disk 1 of the AD8325 Evaluation Software. Follow

the on-screen instructions and insert Disk 2 when prompted to

do so. Enter the path of the directory into which the software

will be installed and select the button in the upper left corner to

complete the installation.

Running the Software

To invoke the control software, go to START -> PROGRAMS

-> CABDRIVE_25, or select the AD8325.EXE icon from the

directory containing the software.

Controlling the Gain/Attenuation of the AD8325

The slide bar controls the AD8325’s gain/attenuation, which is

displayed in dB and in V/V. The gain scales at 0.7526 dB per

LSB with the valid codes being from decimal 0 to 79. The gain

code (i.e., position of the slide bar) is displayed in decimal, binary,

and hexadecimal (see Figure 8).

Transmit Enable, Transmit Disable, and Sleep

The “Transmit Enable” and “Transmit Disable” buttons select

the mode of operation of the AD8325 by controlling the logic

level on the asynchronous TXEN pin. The “Transmit Enable”

button applies a Logic 1 to the TXEN pin putting the AD8325

in forward transmit mode. The “Transmit Disable” button

applies a Logic 0 to the TXEN pin selecting reverse mode, where

the forward signal transmission is disabled while a back termina-

tion of 75

Ω is maintained. On early revisions of the software,

the “Transmit Enable” and “Transmit Disable” buttons may be

called “Power-Up” and “Power-Down” respectively. Checking

the “Enable SLEEP Mode” box applies a Logic 0 to the asyn-

chronous

SLEEP pin, putting the AD8325 into SLEEP mode.

Memory Section

The “MEMORY” section of the software provides a convenient

way to alternate between two gain settings. The “X->M1” but-

ton stores the current value of the gain slide bar into memory

while the “RM1” button recalls the stored value, returning the

gain slide bar to that level. The “X->M2” and “RM2” buttons

work in the same manner.