AD8375-EVALZ datasheet(13/24 Pages) AD

13 / 24 page

AD8375

Rev. 0 | Page 13 of 24

APPLICATIONS

BASIC CONNECTIONS

Figure 35 shows the basic connections for operating the

AD8375. A voltage between 4.5 V and 5.5 V should be applied

to the supply pins. Each supply pin should be decoupled with at

least one low inductance, surface-mount ceramic capacitor of

0.1 μF placed as close as possible to the device.

The outputs of the AD8375 are open collectors that need to be

pulled up to the positive supply with 1 μH RF chokes. The

differential outputs are biased to the positive supply and require

ac coupling capacitors, preferably 0.1 μF. Similarly, the input

pins are at bias voltages of about 2 V above ground and should

be ac-coupled as well. The ac coupling capacitors and the RF

chokes are the principle limitations for operation at low

frequencies.

To enable the AD8375, the PWUP pin must be pulled high.

Taking PWUP low puts the AD8375 in sleep mode, reducing

current consumption to 5 mA at ambient.

SINGLE-ENDED-TO-DIFFERENTIAL CONVERSION

The AD8375 can be configured as a single-ended input to

differential output driver as shown in Figure 33. A 150 Ω

resistor in parallel with the input impedance of input pin

provides an impedance matching of 50 Ω. The voltage gain and

the bandwidth of this configuration, using a 150 Ω load,

remains the same as when using a differential input.

0.1µF

37.5Ω

150Ω

AD8375

1µH

150Ω

A0 TO A4

1µH

+5V

VCM

0.1µF

50Ω

Figure 33. Single-Ended-to-Differential Conversion

Using a single-ended input decreases the power gain by 3 dB

and limits distortion cancellation. Consequently, the second-

order distortion is degraded. The third-order distortion remains

low to 200 MHz, as shown in Figure 34.

–60

–65

–70

–75

–80

–85

–90

–95

–100

200

150

100

FREQUENCY (MHz)

HD2

HD3

Figure 34. Harmonic Distortion vs. Frequency of

Single-Ended-to-Differential Conversion

PARALLEL CONTROL INTERFACE

0.1µF

BALANCED

SOURCE

0.1µF

+VS

BALANCED

LOAD

1µH

0.1µF

10µF

+VS

COMM VPOS COMM COMM COMM PWUP

VPOS VPOS COMM VPOS

VCOM

VIN+

VIN–

VOUT–

VOUT+

VOUT–

VOUT+

COMM

VPOS

AD8375

Figure 35. Basic Connections

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