Datasheet

Data Sheet AD8375
Rev. A | 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.
5
0.1µF
0.1µF
0.1µF
0.1µF
37.5Ω
150Ω
AD8375
1µH
150Ω
A0 TO A4
1µH
+5V
06724-035
VCM
0.1µF
50Ω
AC
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.
06724-036
–60
–65
–70
–75
–80
–85
–90
–95
–100
HARMONIC DISTORTION (dBc)
0 200
15010050
FREQUENCY (MHz)
HD2
HD3
Figure 34. Harmonic Distortion vs. Frequency of
Single-Ended-to-Differential Conversion
PARALLEL CONTROL INTERFACE
0.1µF
0.1µF
0.1µF
R
S
2
R
S
2
AC
BALANCED
SOURCE
0.1µF
0.1µF
+V
S
R
L
BALANCED
LOAD
1µH
1µH
0.1µF
0.1µF
0.1µF
10µF
+V
S
06724-034
COMM VPOS COMM COMM COMM PWUP
1924 23 22 21 20
A1 A0 VPOS VPOS COMM VPOS
127 8 9 10 11
18
17
16
15
14
13
1
2
3
4
5
6
VCOM
VIN+
VIN–
A4
A3
A2
VOUT–
VOUT+
VOUT–
VOUT+
COMM
VPOS
AD8375
Figure 35. Basic Connections