AD8327 Analog Devices, AD8327 Datasheet - Page 11

• Manufacturer Part Number: AD8327
• Description: 5 V CATV Line Driver Coarse Step Output Power Control
• Manufacturer: Analog Devices

Noise and DOCSIS
At minimum gain, the AD8327 output noise spectral density is
11 nV/√Hz measured at 10 MHz. DOCSIS Table 4-8,“Spurious
Emissions in 5 MHz to 42 MHz,” specifies the output noise for
various symbol rates. The calculated noise in dBmV for
160
Comparing the computed noise power of –47 dBmV to the
+8 dBmV signal yields –55 dBc, which meets the required level
set forth in DOCSIS Table 4-8. As the AD8327 gain is increased
above this minimum value, the output signal increases at a faster
rate than the noise, resulting in a signal to noise ratio that improves
with gain. In transmit disable mode, the output noise spectral
density is 1.3 nV/√Hz, which results in –66 dBmV when computed
over 160 K
output of the AD8327AR-EVAL board.
Evaluation Board Features and Operation
The AD8327 evaluation board (Part #AD8327AR-EVAL) and
control software can be used to control the AD8327 upstream
cable driver via the parallel port of a PC. A standard printer
cable connected between the parallel port of the personal com-
puter is used to feed all the necessary data to the AD8327 using
the Windows-based control software. This package provides a
means of evaluating the amplifier with a convenient way to
program the gain/attenuation, as well as offering easy control of
the asynchronous TXEN and SLEEP pins. With this evaluation
kit, the AD8327 can be evaluated in either a single-ended or
differential input configuration. A schematic of the evaluation
board is provided in Figure 10.
Overshoot on PC Printer Ports
The data lines on some PC parallel printer ports have excessive
overshoot that may cause communications problems when pre-
sented to the CLK pin of the AD8327. The evaluation board
was designed to accommodate a series resistor and shunt capaci-
tor (R2 and C5 in Figure 10) to filter the CLK signal if required.
Installing Visual Basic Control Software
Install the “CabDrive_27” software by running “setup.exe” on
disk one of the AD8327 Evaluation Software. Follow on-screen
directions and insert disk two when prompted. Choose installa-
tion directory, and then select the icon in the upper left
to complete installation.
KSYM/SECOND


 

20
log
SYM/S




. The noise power was measured directly at the



is:
11
Hz
nV

 ×

2
160
kHz






 

+
60
=
–
47
dBmV
Running AD8327 Software
To load the control software, go to START, PROGRAMS,
CABDRIVE_27, or select the AD8327.exe from the installed
directory. Once loaded, select the proper parallel port to com-
municate with the AD8327 (Figure 8).
Controlling Gain/Attenuation of the AD8327
The slide bar controls the gain/attenuation of the AD8327,
which is displayed in dB and in V/V. The gain scales 6 dB per
major carry. The gain code from the position of the slide bar is
displayed in decimal, binary, and hexadecimal (Figure 9).
AD8327