AD8324 Datasheet, PDF (13/16 Pages) Analog Devices – 3.3 V Upstream Cable Line Driver

EVALUATION BOARD FEATURES AND OPERATION
The AD8324 evaluation board and control software can be used
to control the AD8324 upstream cable driver via the parallel
port of a personal computer. A standard printer cable connected
to the parallel port of the PC is used to feed all the necessary
data to the AD8324 using the Windows® based control software.
This package provides a means of controlling the gain and the
power mode of the AD8324. With this evaluation kit, the
AD8324 can be evaluated in either a single-ended or differential
input configuration. A schematic of the evaluation board is
provided in Figure 29.
DIFFERENTIAL SIGNAL SOURCE
Typical applications for the AD8324 use a differential input
signal from a modulator or a DAC. Refer to Table 7 for common
values of R4, or calculate other input configurations using the
equation in Figure 24. This circuit configuration will give
optimal distortion results due to the symmetric input signals. It
should be noted that this is the configuration that was used to
characterize the AD8324.
V_IN+
Z_IN
V_IN–
R4 = ^{ZIN × 1100Ω}
1100Ω – Z_IN
R4
AD8324
Figure 24. Differential Circuit
DIFFERENTIAL SIGNAL FROM
SINGLE-ENDED SOURCE
The default configuration of the evaluation board implements a
differential signal drive from a single-ended signal source. This
configuration uses a 1:1 balun transformer to approximate a
differential signal. Because of the non-ideal nature of real
transformers, the differential signal is not purely equal and
opposite in amplitude. Although this circuit slightly sacrifices
even order harmonic distortion due to asymmetry, it does
provide a convenient way to evaluate the AD8324 with a single-
ended source. The AD8324 evaluation board is populated with a
TOKO 617DB-A0070 1:1 for this purpose (T1).
Table 7 provides typical R4 values for common input
configurations. R16 must be removed, and R2 and R3 should be
shorted. Other input impedances may be calculated using the
equation in Figure 25. Refer to Figure 29 for an evaluation
board schematic. To use the transformer for converting a single
ended source into a differential signal, the input signal must be
applied to VIN+.
V_IN+
Z_IN
R4 = ^{ZIN × 1100Ω}
1100Ω – Z_IN
AD8324
R4
AD8324
Figure 25. Single-to-Differential Circuit
SINGLE-ENDED SOURCE
Although the AD8324 was designed to have optimal DOCSIS
performance when used with a differential input signal, the
AD8324 may also be used as a single-ended receiver, or as an IF
digitally controlled amplifier. However, as with the single-ended
to differential configuration noted previously, even order
harmonic distortion will be slightly degraded.
When operating the AD8324 in a single-ended input mode,
terminate the part as illustrated in Figure 26. On the AD8324
evaluation boards, this termination method requires the
removal and shorting of R2 and R3, the removal of R4, as well
as the addition of 86.6 Ω at R1 and 40.2 Ω at R17 for 75 Ω
termination. Table 7 shows the correct values for R11 and R12
for some common input configurations. Other input impedance
configurations may be accommodated using the equations in
Figure 26.
R1 = ^{ZIN × 550}
550 – Z_IN
R17 = ^{ZIN × R1}
R1 – Z_IN
V_IN+
R1
Z_IN
AD8324
R17
Figure 26. Single-Ended Circuit
Table 7. Common Matching Resistors
Differential Input Termination
ZIN (Ω)
R2/R3 (Ω)
R4 (Ω)
R1/R17 (Ω)
50
Open
52.3
Open/Open
75
Open
80.6
Open/Open
100
Open
110
Open/Open
150
Open
174
Open/Open
Single-Ended Input Termination
ZIN (Ω)
R2/R3 (Ω)
R4 (Ω)
R1/R17 (Ω)
50
0/0
Open
54.9/26.1
75
0/0
Open
86.6/40.2
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