ADL5375-05ACPZ-R7 Analog Devices Inc, ADL5375-05ACPZ-R7 Datasheet - Page 23

• Manufacturer Part Number: ADL5375-05ACPZ-R7
• Description: IC MOD QUAD 400MHZ-6GHZ 24LFCSP
• Manufacturer: Analog Devices Inc

Specifications of ADL5375-05ACPZ-R7

• Design Resources: Interfacing ADL5375 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0021) Broadband Low EVM Direct Conversion Transmitter (CN0134)
• Function: Modulator
• Lo Frequency: 400MHz ~ 6GHz
• Rf Frequency: 400MHz ~ 6GHz
• P1db: 10.4dBm
• Noise Floor: -157.6dBm/Hz
• Output Power: 1.71dBm
• Current - Supply: 200mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Test Frequency: 3.5GHz
• Package / Case: 24-VFQFN, 24-CSP Exposed Pad
• Frequency Range: 400MHz To 6GHz
• Rf Type: Quadrature
• Supply Voltage Range: 4.75V To 5.25V
• Rf Ic Case Style: LFCSP
• No. Of Pins: 24
• Operating Temperature Range: -40°C To +85°C
• Frequency Max: 6GHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ADL5375-05ACPZ-R7TR

APPLICATIONS INFORMATION
DAC MODULATOR INTERFACING
Driving the ADL5375-05 with a TXDAC®
The ADL5375-05 is designed to interface with minimal
components to members of the Analog Devices, Inc. TxDAC
families. These dual-channel differential current output DACs
feature an output current swing from 0 mA to 20 mA. The
interface described in this section can be used with any DAC
that has a similar output.
An example of an interface using the
shown in Figure 57. The baseband inputs of the ADL5375-05
require a dc bias of 500 mV. The average output current on each
of the outputs of the AD9779A 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 ADL5375-05.
The AD9779A output currents have a swing that ranges from
0 mA to 20 mA. With the 50 Ω resistors in place, the ac voltage
swing going into the ADL5375-05 baseband inputs ranges from 0
V to 1 V. A full-scale sine wave out of the AD9779A 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 the shunt between each side of the
differential pair, as shown in Figure 58. It has the effect of
reducing the ac swing without changing the dc bias already
established by the 50 Ω resistors.
AD9779A
Resistors to Ground to Establish the 500 mV DC Bias for the ADL5375-05
Figure 57. Interface Between the AD9779A and ADL5375-05 with 50 Ω
OUT1_P
OUT1_N
OUT2_N
OUT2_P
92
93
84
83
RBQN
RBQP
RBIP
RBIN
50Ω
50Ω
50Ω
50Ω
Baseband Inputs
AD9779A
21
22
10
9
TxDAC is
ADL5375-05
IBBP
IBBN
QBBN
QBBP
Rev. A | Page 23 of 32
The value of this ac voltage swing limiting resistor is chosen
based on the desired ac voltage swing. Figure 59 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
It is necessary to place an antialiasing filter between the DAC
and modulator to filter out Nyquist images and broadband
DAC noise. The interface for setting up the biasing and ac
swing discussed in the Limiting the AC Swing section lends
itself well to the introduction of such a filter. The filter can be
inserted between the dc bias setting resistors and the ac swing-
limiting resistor. Doing so establishes the input and output
impedances for the filter.
Figure 60 shows a third-order, Bessel low-pass filter with a 3 dB
frequency of 10 MHz. Matching input and output impedances
make the filter design easier, so the shunt resistor chosen is
100 Ω, producing an ac swing of 1 V p-p differential. The
frequency response of this filter is shown in Figure 61.
AD9779A
Figure 59. Relationship Between the AC Swing-Limiting Resistor and the
OUT1_P
OUT1_N
OUT2_N
OUT2_P
Figure 58. AC Voltage Swing Reduction Through the Introduction
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Peak-to-Peak Voltage Swing with 50 Ω Bias-Setting Resistors
0
10
93
92
84
83
of a Shunt Resistor Between Differential Pair
RBQN
RBQP
RBIP
RBIN
50Ω
50Ω
50Ω
50Ω
100
R
L
(Ω)
RSLQ
100Ω
100Ω
RSLI
1000
21
22
10
9
ADL5375-05
ADL5375
IBBP
IBBN
QBBN
QBBP
10000