REV. 0

AD8323

–9–

Distortion, Adjacent Channel Power, and DOCSIS

In order to deliver 58 dBmV of high fidelity output power

required by DOCSIS, the PA should be able to deliver about

60 dBmV to 61 dBmV in order to make up for losses associated

with the transformer and diplexer. It should be noted that the

AD8323 was characterized with the TOKO 617DB-A0070

transformer. TPC 7 and TPC 8 show the AD8323 second and

third harmonic distortion performance versus fundamental

frequency for various output power levels. These figures are

useful for determining the inband harmonic levels from 5 MHz to

65 MHz. Harmonics higher in frequency will be sharply attenu-

ated by the low-pass filter function of the diplexer. Another

measure of signal integrity is adjacent channel power or ACP.

DOCSIS section 4.2.9.1.1 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.”

Figure 7 shows the measured ACP for a 16 QAM, 60 dBmV

signal, taken at the output of the AD8323 evaluation board (see

Figure 13 for evaluation board schematic). The transmit chan-

nel width and adjacent channel width in Figure 7 correspond to

the AD8323 for all conditions in DOCSIS Table 4-7 “Adjacent

Channel Spurious Emissions.”

–10

–20

–30

–40

–70

–50

–60

–80

CENTER 10 MHz

60 kHz

SPAN 600 kHz

CL1

C0

C0

CU1

CL1

RBW 500 Hz RF ATT 40dB

VBW 5 kHz

SWT 12s UNIT dBm

CH PWR

5.44 dBm

ACP UP

–52.99 dB

ACP LOW

–54.36 dB

F1

CU1

Figure 7. Adjacent Channel Power

Table I. ACP Performance for All DOCSIS Conditions

(All Values in dBc)

TRANSMIT

CHANNEL

SYMBOL RATE

–53.0

ADJACENT CHANNEL SYMBOL RATE

–53.8

–55.0

–56.6

–56.3

–52.7

–53.4

–53.8

–54.8

–55.4

–53.8

–52.9

–53.3

–53.6

–54.2

–53.7

–53.4

–53.0

–53.3

–53.5

–55.4

–54.0

–53.6

–53.1

–53.3

Noise and DOCSIS

At minimum gain, the AD8323’s output noise spectral density is

10 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 power in dBmV for

20

10

160

60

48

2

log

–

nV

Hz

kHz

dBmV











 ×





































+=

Comparing the computed noise power of –48 dBmV to the

8 dBmV signal yields –56 dBc, which meets the required level of

–53 dBc set forth in DOCSIS Table 4-8. As the AD8323’s gain is

increased from 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

√Hz

or –68 dBmV.

Evaluation Board Features and Operation

The AD8323 evaluation board (Part # AD8323-EVAL) and

control software can be used to control the AD8323 upstream

cable driver via the parallel port of a PC. A standard printer

cable connected between the parallel port and the evaluation

board is used to feed all the necessary data to the AD8323 by

means of the Windows-based, Microsoft Visual Basic 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 amplifiers’

asynchronous

PD and SLEEP pins. With this evaluation kit the

AD8323 can be evaluated with 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. To remove

the diplexer from the signal path, move the 0

Ω chip resistor at

JP5 so the output signal is directed away from the diplexer

and toward the CABLE port of the evaluation board. Also,

remove the 0

Ω resistor at JP4. A schematic of the evaluation

board is provided in Figure 13.

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 AD8323 (TP5 on the evaluation

board). The evaluation board was designed to accommodate a

series resistor and shunt capacitor (R1 and C15) to filter the

CLK signal if required.

Transformer and Diplexer

A 1:1 transformer is needed to couple the differential outputs of

the AD8323 to the cable while maintaining a proper impedance

match. The specified transformer is available from TOKO (Part

# 617DB-A0070); however, MA/COM part # ETC-1-1T-15

can also be used. The evaluation board is equipped with the

TOKO transformer, but is also designed to accept the MA/

COM transformer. The PULSE diplexer included on the

evaluation board provides a high-order low-pass filter function,

typically used in the upstream path. 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.

Differential Inputs

The AD8323-EVAL evaluation board is designed to accommodate

a Mini-Circuits T1-6T-KK81 1:1 transformer for the purpose of

converting a single-ended (ground-referenced) input signal to

differential inputs. Figure 8 and the following paragraphs identify

two options for providing differential input signals to the AD8323

evaluation board.