ADL5385ACPZ-R7 Analog Devices Inc, ADL5385ACPZ-R7 Datasheet - Page 15

• Manufacturer Part Number: ADL5385ACPZ-R7
• Description: IC, QUAD MODULATOR 50MHZ-2.2GHZ LFCSP-24
• Manufacturer: Analog Devices Inc

Specifications of ADL5385ACPZ-R7

• Frequency Range: 50MHz To 2.2GHz
• Rf Type: Quadrature
• Supply Voltage Range: 4.75V To 5.5V
• Rf Ic Case Style: LFCSP
• No. Of Pins: 24
• Operating Temperature Range: -40°C To +85°C
• Design Resources: Broadband Low EVM Direct Conversion Transmitter Using LO Divide-by-2 Modulator (CN0144)
• Function: Modulator
• Lo Frequency: 50MHz ~ 2.2GHz
• Rf Frequency: 50MHz ~ 2.2GHz
• P1db: 8dBm
• Noise Floor: -160dBm/Hz
• Output Power: 2.6dBm
• Current - Supply: 240mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Test Frequency: 2.15GHz
• Package / Case: 24-VFQFN, 24-CSP Exposed Pad
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ADL5385ACPZ-R7TR

APPLICATIONS
DAC MODULATOR INTERFACING
The ADL5385 is designed to interface with minimal components
to members of the Analog Devices family of digital-to-analog
converters (DAC). These DACs feature an output current swing
from 0 to 20 mA, and the interface described in this section can
be used with any DAC that has a similar output.
Driving the ADL5385 with an Analog Devices TxDAC®
An example of the interface using the AD9777 TxDAC is shown
in Figure 31. The baseband inputs of the ADL5385 require a dc
bias of 500 mV. The average output current on each of the
outputs of the AD9777 is 10 mA. Therefore, a single 50 Ω
resistor to ground from each of the DAC outputs results in an
average current of 10 mA flowing through each of the resistors,
thus producing the desired 500 mV dc bias for the inputs to the
ADL5385.
The AD9777 output currents have a swing that ranges from
0 to 20 mA. With the 50 Ω resistors in place, the ac voltage
swing going into the ADL5385 baseband inputs ranges from
0 V to 1 V. A full-scale sine wave out of the AD9777 can be
described as a 1 V p-p single-ended (or 2 V p-p differential)
sine wave with a 500 mV dc bias.
Limiting the AC Swing
There are situations in which it is desirable to reduce the
ac voltage swing for a given DAC output current. This can be
achieved through the addition of another resistor to the
interface. This resistor is placed in shunt between each side of
the differential pair, as illustrated in Figure 32. It has the effect
of reducing the ac swing without changing the dc bias already
established by the 50 Ω resistors.
Ground to Establish the 500 mV DC Bias for the ADL5385 Baseband Inputs
Figure 31. Interface Between AD9777 and ADL5385 with 50 Ω Resistors to
AD9777
I
I
I
I
OUTA1
OUTB1
OUTB2
OUTA2
73
72
69
68
RBQN
RBQP
RBIN
RBIP
50Ω
50Ω
50Ω
50Ω
17
18
13
14
ADL5385
QBBN
QBBP
IBBP
IBBN
Rev. 0 | Page 15 of 24
The value of this ac voltage swing-limiting resistor is chosen
based on the desired ac voltage swing. Figure 33 shows the
relationship between the swing-limiting resistor and the peak-
to-peak ac swing that it produces when 50 Ω bias-setting
resistors are used.
Filtering
When driving a modulator from a DAC, it is necessary to
introduce a low-pass filter between the DAC and the modulator
to reduce the DAC images. The interface for setting up the
biasing and ac swing lends itself well to the introduction of such
a filter. The filter can be inserted in between the dc bias setting
resistors and the ac swing-limiting resistor, thus establishing the
input and output impedances for the filter.
Examples of filters are discussed in the 155 MBPS (STM-1) 128
QAM Transmitter and the CMTS Transmitter Application
sections.
AD9777
Figure 32. AC Voltage Swing Reduction Through Introduction of Shunt
I
I
I
I
Figure 33. Relationship Between AC Swing-Limiting Resistor and
OUTA1
OUTB1
OUTB2
OUTA2
Peak-to-Peak Voltage Swing with 50 Ω Bias-Setting Resistors
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
10
73
72
69
68
RBQN
RBQP
RBIP
RBIN
50Ω
50Ω
50Ω
50Ω
Resistor Between Differential Pair
100
R
L
(Ω)
RSLQ
100Ω
100Ω
RSLI
1000
17
18
13
14
ADL5385
ADL5385
QBBN
QBBP
IBBN
IBBP
10000