Datasheet AD8325 (Analog Devices) - 10

AD8325 Differential Inputs Installing the Visual Basic Control Software
The AD8325-EVAL evaluation board may be driven with a To install the “CABDRIVE_25” evaluation board control soft­ differential signal in one of two ways. A transformer may be ware, close all Windows applications and then run “SETUP.EXE” used to convert a single-ended signal to differential, or a differ­ located on Disk 1 of the AD8325 Evaluation Software. Follow ential signal source may be used. Figure 7 and the following the on-screen instructions and insert Disk 2 when prompted to paragraphs describe each of these methods. do so. Enter the path of the directory into which the software
Single-Ended-to-Differential Input (Figure 7, Option 1)
will be installed and select the button in the upper left corner to A TOKO 617DB-A0070 1:1 transformer is preinstalled in the complete the installation. T3 location of the evaluation board. Install 0 W chip resistors at
Running the Software
R14, R15, and R20, and leave R16 through R19 open. For To invoke the control software, go to START -> PROGRAMS 50 W differential input impedance, install a 51.1 W resistor at R13. -> CABDRIVE_25, or select the AD8325.EXE icon from the For 75 W differential input impedance, use a 78.7 W resistor. directory containing the software. In this configuration, the input signal must be applied to the
Controlling the Gain/Attenuation of the AD8325
VIN+ port of the evaluation board. For input impedances other The slide bar controls the AD8325’s gain/attenuation, which is than 50 W or 75 W, the correct value for R13 can be calculated displayed in dB and in V/V. The gain scales at 0.7526 dB per using the following equation. LSB with the valid codes being from decimal 0 to 79. The gain Desired Input Impedance = (R131600) code (i.e., position of the slide bar) is displayed in decimal, binary,
Differential Input (Figure 7, Option 2)
and hexadecimal (see Figure 8). If a differential signal source is available, it may be applied
Transmit Enable, Transmit Disable, and Sleep
directly to both the VIN+ and VIN– input ports of the evaluation The “Transmit Enable” and “Transmit Disable” buttons select board. In this case, 0 W chip resistors should be installed at the mode of operation of the AD8325 by controlling the logic locations R16 through R19, and R14, R15, and R20 should be level on the asynchronous TXEN pin. The “Transmit Enable” left open. The equation at the end of the preceding paragraph button applies a Logic 1 to the TXEN pin putting the AD8325 can be used to compute the correct value for R13 for any in forward transmit mode. The “Transmit Disable” button desired differential input impedance. For differential input applies a Logic 0 to the TXEN pin selecting reverse mode, where impedances of 75 W or 150 W, the value of R13 will be 78.7 W or the forward signal transmission is disabled while a back termina­ 165 W respectively. tion of 75 W is maintained. On early revisions of the software, the “Transmit Enable” and “Transmit Disable” buttons may be
DIFF IN
called “Power-Up” and “Power-Down” respectively. Checking
T1 R13 AD8325
the “Enable SLEEP Mode” box applies a Logic 0 to the asyn­ chronous SLEEP pin, putting the AD8325 into SLEEP mode.
Memory Section DIFFERENTIAL INPUT, OPTION 1
The “MEMORY” section of the software provides a convenient way to alternate between two gain settings. The “X->M1” but­
V
ton stores the current value of the gain slide bar into memory
IN+ R13 AD8325
while the “RM1” button recalls the stored value, returning the gain slide bar to that level. The “X->M2” and “RM2” buttons
V – IN
work in the same manner.
DIFFERENTIAL INPUT, OPTION 2
Figure 7. Differential Input Termination Options –10– REV. A Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM SPECIFICATIONS LOGIC INPUTS TIMING REQUIREMENTS ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDERING GUIDE PIN FUNCTION DESCRIPTIONS Typical Performance Characteristics APPLICATIONS General Application Operational Description SPI Programming and Gain Adjustment Input Bias, Impedance, and Termination Output Bias, Impedance, and Termination Power Supply Decoupling, Grounding, and Layout Considerations Initial Power-Up Between Burst Operation Distortion, Adjacent Channel Power, and DOCSIS Noise and DOCSIS Evaluation Board Features and Operation Overshoot on PC Printer Ports Transformer and Diplexer Differential Inputs Single-Ended-to-Differential Input Differential Input Installing the Visual Basic Control Software Running the Software Controlling the Gain/Attenuation of the AD8325 Transmit Enable, Transmit Disable, and Sleep Memory Section EVALUATION BOARD FEATURES AND OPERATION EVALUATION BOARD BILL OF MATERIALS OUTLINE DIMENSIONS Revision History