AD8326ARE Analog Devices Inc, AD8326ARE Datasheet - Page 13

• Manufacturer Part Number: AD8326ARE
• Description: IC LINE DVR CATV PROG 28-TSSOP
• Manufacturer: Analog Devices Inc
• Type: Line Driver, Transmitterr

Specifications of AD8326ARE

• Rohs Status: RoHS non-compliant
• Applications: CATV
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• For Use With: AD8326ARE-EVAL - BOARD EVAL FOR AD8326 TSSOP

Distortion, Adjacent Channel Power, and DOCSIS
In order to deliver +58 dBmV of high fidelity output power
required by DOCSIS, the PA is required to deliver up to
+67 dBmV. This added power is required to compensate for
losses associated with the transformer, diplexer, directional
coupler, and splitters that may be included in the upstream
path of the cable telephony. It should be noted that the AD8326
was characterized with the TOKO 617DB-A0070 transformer.
TPC 7, TPC 8, TPC 13, and TPC 14 show the AD8326 second
and third harmonic distortion performance versus fundamental
frequency for various output power levels. These figures are
useful for determining the in band harmonic levels from 5 MHz
to 65 MHz. Harmonics higher in frequency will be sharply
attenuated by the low-pass filter function of the diplexer.
Another measure of signal integrity is adjacent channel power,
commonly referred to as ACP. DOCSIS section 4.2.10.1.1
states, “Spurious emissions from a transmitted carrier may
occur in an adjacent channel that could be occupied by a carrier
of the same or different symbol rates.” TPC 9 shows the mea-
sured ACP for a +67 dBmV 16 QAM signal taken at the output
of the AD8326 evaluation board, through a 75
matching pad (5.7 dB of loss). The transmit channel width
and adjacent channel width in TPC 9 correspond to symbol
rates of 160 KSYM/SEC. Table I shows the ACP results for
the AD8326 for all conditions in DOCSIS Table 4-7 “Adjacent
Channel Spurious Emissions.”
Transmit
Symbol
Rate
160K/s
320K/s
640K/s
1280K/s
2560K/s
Noise and DOCSIS
At minimum gain, the AD8326 output noise spectral density is
13.3 nV/ Hz measured at 10 MHz. DOCSIS Table 4-8, “Spuri-
ous Emissions in 5 MHz to 42 MHz,” specifies the output noise
for various symbol rates. The calculated noise power in dBmV
for 160 KSYM/SECOND is:
Comparing the computed noise power of –45.5 dBmV to the
+8 dBmV signal yields –53.5 dBc, which meets the required level
set forth in DOCSIS Table 4-8. As the AD8326 gain is increased
from this minimum value, the output signal increases at a faster
20
log
Adjacent Channel Symbol Rate
Table I. Adjacent Channel Power
160K/s
ACP
(dBc)
–57
–57
–55
–55
–53
13 3
.
Hz
nV
2
320K/s
ACP
(dBc)
–59
–58
–58
–57
–56
160
kHz
640K/s
ACP
(dBc)
–62
–60
–58
–58
–57
60
1280K/s 2560K/s
ACP
(dBc)
–63
–62
–60
–58
–57
–
45 5
to 50
.
dBmV
ACP
(dBc)
–64
–64
–62
–60
–57
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 1.4 nV/ Hz, which results in –65 dBmV when computed
over 160
The noise power was measured directly at the output of the
transformer. In a typical cable telephony application there will
be a 6 dB pad, or splitter, which will further attenuate the noise
by 6 dB.
Evaluation Board Features and Operation
The AD8326 evaluation boards (Part # AD8326ARE-EVAL
and AD8326ARP-EVAL) and control software can be used to
control the AD8326 upstream cable driver via the parallel port
of a PC. A standard printer cable connected between the paral-
lel port and the evaluation board is used to feed all the necessary
data to the AD8326 by means of the Windows 9X-based control
software. This package provides a means of evaluating the amplifier
by providing 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 AD8326 can be evalu-
ated in either a single-ended or differential input configuration.
The amplifier can also be evaluated with or without the PULSE
diplexer in the output signal path. A schematic of the evaluation
board is provided in Figure 11.
Output Transformer and Diplexer
A 1:1 transformer is needed to couple the differential outputs of
the AD8326 to the cable while maintaining a proper impedance
match. The specified transformer is available from TOKO (Part
# 617DB-A0070); however, M/A-COM part # ETC-1-1T may
also be used. The evaluation board is equipped with the TOKO
transformer, but is also designed to accept the M/A-COM trans-
former. The PULSE diplexer included on the evaluation board
provides a high-order low-pass filter function, typically used in the
upstream path. To remove the diplexer from the signal path,
remove the 0
chip resistor at R6 so the output signal is directed away from
the diplexer and toward the CABLE port of the evaluation
board (Figure 11). The ability of the PULSE diplexer to achieve
DOCSIS compliance is neither expressed nor implied by Analog
Devices Inc. Data on the diplexer should be obtained from
PULSE. When using the diplexer, be sure to properly terminate
the cable port (75 ) so that the AD8326 draws minimal current.
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 AD8326. The evaluation board
was designed to accommodate a series resistor and shunt capaci-
tor (R2 and C2 in Figure 11) to filter the CLK signal if required.
Installing Visual Basic Control Software
Install the “CabDrive_26” software by running “setup.exe” on
disk one of the AD8326 Evaluation Software. Follow on-screen
directions and insert disk two when prompted. Choose instal-
lation directory, and then select the icon in the upper left to
complete installation.
KSYM/SECOND
chip resistors at R7 and R19, and install a 0
.
AD8326