AD8324

Rev. 0 | Page 13 of 16

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.

AD8324

R4

R4 =

1100

Ω – Z

IN

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

AD8324

R4

R4 =

1100

Ω – Z

IN

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.

AD8324

R1

R17

R1 =

R17 =

Figure 26. Single-Ended Circuit

Table 7. Common Matching Resistors

Differential Input Termination

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

R2/R3 (Ω)

R4 (Ω)

R1/R17 (Ω)

50

0/0

Open

54.9/26.1

75

0/0

Open

86.6/40.2