AD8326ARP datasheet(11/24 Pages) AD

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REV. 0

AD8326

–11–

Input Bias, Impedance, and Termination

The VIN+ and VIN– inputs have a dc bias level of approxi-

mately 1.47 V below VCC/2, therefore the input signal should

be ac-coupled using 0.1

µF capacitors as seen in the typical

application circuit (see Figure 5).

The differential input impedance of the AD8326 is approxi-

mately 1600

Ω, while the single-ended input is 800 Ω.

Single-Ended Inverting Input

When operating the AD8326 in a single-ended input mode VIN+

and VIN– should be terminated as illustrated in Figure 6. On the

AD8326 evaluation boards, this termination method requires the

removal of R12, R13, R14, R16, R17, and R18. Install a 0

Ω

jumper at R15, an 82.5

Ω resistor at R10 for a 75 Ω system, and a

39.2

Ω resistor at R11 to balance the inputs of the AD8326

evaluation board (Figure 11). Other input impedance configura-

tions may be calculated using the equations in Figure 6.

AD8326

R10

R11

–

ZIN = R10||800

R11 = ZIN||R10

VIN–

Figure 6. Single-Ended Input Impedance

The inverting and noninverting inputs of the AD8326 must be

balanced for all input configurations.

Differential Input from Single-Ended Source

The default configuration of the evaluation board implements a

differential signal drive from a single-ended signal source. A

Toko 1:1 transformer is included on the board for this purpose

(T3). Enabling the evaluation board for single to differential

input conversion requires R15–R17 to be removed, and 0

Ω

jumpers must be installed on the placeholders for R13, R14, and

R18. For a 75

Ω input impedance, R12 should be 78.7 Ω. Refer

to Figure 11 for evaluation board schematic. In this configuration,

the input signal must be applied to VIN–. Other input imped-

ances may be calculated using the equation in Figure 7.

VIN–

AD8326

DESIRED IMPEDANCE = R12||1600

R12

Figure 7. Differential Signal from Single-Ended Source

Differential Signal Source

The AD8326 evaluation board is also capable of accepting a

differential input signal. This requires the installation of a 165

Ω

resistor in R12, the removal of R13–R14, R17–R18, and the

installation of 0

Ω jumpers for R15–R16. This configuration

results in a differential input impedance of 150

Ω. Other differ-

ential input impedance configurations may be calculated with

the equation in Figure 8.

VIN+

AD8326

VIN–

R12

DESIRED IMPEDANCE = R12||1600

Figure 8. Differential Input

DATEN

SDATA

CLK

GND1

VCC

TXEN

SLEEP

GND

VCC

VEE

GND

VEE

VOUT–

GND

VCC

VIN–

VIN+

VEE

VCC

VEE

BYP

VCC

VEE

GND

VEE

VOUT+

AD8326

VEE

TXEN

DATEN

SDATA

CLK

10 F

0.1 F

TOKO 617DB-A0070

TO DIPLEXER

ZIN = 75

0.1 F

165

VIN–

VIN+

ZIN = 150

10 F

VCC

SLEEP

0.1 F

Figure 5. Typical Applications Circuit

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