BRO393_12B.pdf

Applications
• 2G / 3G / 4G wireless
systems
• LTE transceivers
• UHF/VHF public safety
bands
• Macro base stations
• Micro base stations
• Pico base stations
• Femto base stations
• GSM, UMTS,
multistandard
transceivers
• Test and measurement
instrumentation
• Military
communication
Features
• Low insertion loss
• High attenuation
accuracy
• Excellent return loss
• High IP3
• Broad frequency
response
• Flat attenuation
• Monotonic step
response
• Performance out to
4 GHz
• Power control at
IF applications
• SPI control
• Parallel control
• Power up options
• Addressable
• Small QFN lead (Pb)free, RoHS-compliant
packaging
Digital Attenuators with High
Attenuation Range and Accuracy
Select Digital Attenuators Available from Stock for Prototype or
High Volume Production
Skyworks Solutions offers a select group of digital attenuators from our broad product
portfolio that are in stock now and ready for immediate design into your demanding
applications.
Skyworks’ extensive portfolio of RF microwave products includes solutions for wireless
communications infrastructure systems, such as 4G / LTE macro and micro cellular base
stations, high power WLAN access points, land-mobile radio systems, point-to-point radio
links, and more. Skyworks’ solutions attenuate signals in both receive and transmit signal
paths, are controlled by serial or parallel interfaces, and offer attenuation bit accuracy as
great as 0.25 dB.
Select attenuators include the most popular GaAs 1-, 2-, 3-, 4-, 5-, 6-, and 7-bit RF and
IF attenuators, readily available to ship from stock. These devices provide excellent
performance and value for applications such as Tx/Rx power control in transceiver blocks.
All attenuators are designed using Skyworks’ state-of-the-art Pseudomorphic High Electron
Mobility Transistor (pHEMT) process. Some designs incorporate CMOS controllers to
generate negative bias to extend frequency response down to 50 MHz for IF applications.
These designs do not require DC blocking capacitors on the RF lines. The use of CMOS
in the package also provides the functionality of serial port interface (SPI) control as well
as decode logic functions. The CMOS designs draw very little bias control current when
compared to integrating the decode functions on a GaAs design. Select attenuators have
been fully characterized for low-frequency applications, covering the UHF and VHF ranges.
The performance characteristics of the attenuators include: broadband operation (VHF to
4 GHz); attenuation range from 0.25 dB to 31.75 dB; low insertion loss; excellent
attenuation accuracy; monotonic step size; excellent phase performance; fast switching;
and, excellent IIP3 performance. All attenuators are absorptive in 50 W environments and
therefore easily cascadable – impedance matching is not required between attenuators.
Our lead (Pb)-free, RoHS-compliant and Green™ products are fabricated in our high volume
GaAs pHEMT facility. All attenuators are packaged in industry-standard, plastic surfacemount packages. These attenuators leverage the extensive design knowledge, technical
leadership, manufacturing expertise, and superior quality of Skyworks.
A select list of Skyworks digital attenuators is provided in Table 1. Evaluation boards are
available.
An application engineering team is available to assist you with your design efforts.
Application notes and block diagrams are accessible on Skyworks’ Web site:
www.skyworksinc.com
Table 1. Select Digital Attenuators for IF/UHF/VHF and Broadband RF Applications
Part Number
New Products
Frequency
Range
(GHz)
Number
of Bits
Least
Significant
Bit (dB)
Control
Interface
Maximum
Attenuation
(dB)
Typical
Insertion
Loss (dB)
Typical
IIP3
(dBm)
Package
(mm)
AA103-72LF
LF–2.5
1
10
Parallel
10
0.3–0.4
41
SOT-23 5L 2.8 x 2.9 x 1.18
SKY12406-360LF
0.05–0.6
1
12
Parallel
12
0.3
46
QFN 8L 2 x 2 x 0.9
AA116-72LF
0.004–2.0
1
15
Parallel
15
0.35–0.4
41
SOT-23 5L 2.8 x 2.9 x 1.18
AA104-73LF
LF–2.5
1
32
Parallel
32
0.8–1.0
41
SOT-23 6L 2.8 x 2.9 x 1.18
SKY12407-321LF
0.05–0.6
2
12
Parallel
12 (100 W
Differential I/O)
0.3
48
QFN 12L 3 x 3 x 0.75
SKY12324-73LF
0.3–3.0
2
4
Parallel
12
0.9–1.3
43
SOT-23 6L 2.8 x 2.9 x 1.18
SKY12338-337LF
0.35–4.0
2
6
Parallel
18
0.55–1.3
45
QFN 12L 3 x 3 x 0.75
SKY12325-350LF
0.5–6.0
3
1
Parallel
7
0.7–1.3
47
QFN 16L 3 x 3 x 0.75
SKY12348-350LF
0.1–3.0
4
1
Parallel
15
0.8–1.2
45
QFN 16L 3 x 3 x 0.75
SKY12340-364LF
0.3–2.0
5
0.5
SPI
15.5
1.4–1.8
45
QFN 32L 5 x 5 x 0.9
SKY12322-86LF
0.5–4.0
5
0.5
Parallel
15.5
1.4–3.0
45
MSOP 10L 4.9 x 3 x 0.96
SKY12323-303LF
0.5–3.0
5
1
Parallel
31
1.4–2.3
48
MSOP 10L 4.9 x 3 x 0.96
SKY12328-350LF
0.5–4.0
5
0.5
Parallel
15.5
1.1–2.3
42
QFN 16L 3 x 3 x 0.75
SKY12339-350LF
0.4–3.0
5
1
Parallel
31
1.2–2.0
39
QFN 12L 3 x 3 x 0.75
SKY12345-362LF
0.7–4.0
5
0.5
SPI
15.5
1.2–2.0
42
QFN 24L 4 x 4 x 0.9
SKY12347-362LF
LF–3.0
6
0.5
SPI or Parallel
31.5
1.2–2.0
50
QFN 24L 4 x 4 x 0.9
SKY12343-364LF
0.01–4.0
7
0.25
SPI or Parallel
31.75
1.8–1.9
50
QFN 32L 5 x 5 x 0.9
Skyworks Green™ products are compliant to all applicable materials legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074.
All parts are lead (Pb)-free and RoHS-compliant.
Digital Attenuator Fundamentals
Skyworks utilizes the same process to fabricate RF
switches as our digital attenuators, with an additional thin
film resistor layer to create highly accurate attenuation
structures. The thin film resistors are configured in either
a p or a T-type configuration in order to provide the
best attenuation accuracy and impedance match versus
frequency. The p or T configured resistors are switched
into or out of the signal path to either “click in” or “click
out” the attenuation bit. (See Figure 1) .
Figure 1. p and T Configured Attenuators
Multiple bits can be cascaded to increase attenuation
range. Typically the bit values are binary weighted. The
smallest value, which is the least amount of attenuation
the attenuator can produce, is called the least significant
bit (LSB). The largest value, or highest attenuation bit, is
called the most significant bit (MSB). The individual bits
can be switched into or out of the signal path to produce
the desired total attenuation versus control signal(s)
resulting in a transfer function which resembles a stair
step function when plotted. The physical placement of
the attenuator stages on the GaAs substrate is optimized
to maintain the best match throughout the entire
attenuation range. The control lines are routed on the
chip to make it easy for the user to bias and control the
attenuator in a logical, effective way.
V1
V3
V2
P/S
CLOCK
DATA_IN
LATCH_ENABLE
V5
V4
V6
V7
VDD
A2
A1
A0
Serial or Parallel Driver
RF1
RF2
0.25 dB
8 dB
4 dB
2 dB
1 dB
0.5 dB
16 dB
S2122
Figure 2. SKY12347-364LF Example of 7-Bit Attenuator
The use of CMOS provides several advantages. Functions
such as negative voltage generators (NVG), serial port
interface (SPI) and logic decoders are readily implemented
in a CMOS process. When using an NVG, the user applies
a positive supply voltage from which circuitry on the
CMOS chip generates a negative voltage to bias the GaAs
attenuator. Since the GaAs pHEMT Field-Effect Transistors
(FETs) are depletion mode devices, they must be biased
with a negative voltage at the gate with respect to the
voltage at the drain/source. The use of an NVG also
precludes the need for DC blocking capacitors on the RF
lines and allows the GaAs attenuator bits to be connected
directly to ground without an RF bypass cap. These design
techniques are employed for most IF attenuators.
100 pF
DC Control 1
V1
13
V2
V4
1
DC Power
14
V3
15
16
DC Control 2
DC Control 3
DC Control 4
An alternate method to extend the frequency response
down to UHF/VHF frequencies is to float the attenuator
with an external capacitor. (See Figure 3).
N/C
VDD
2
N/C
RFGND1
N/C
RFGND2
4
N/C
5
330 pF
6
RFGND4
3
RF2
N/C
×
RF1
RFGND3
RF Port 1
7
12
×
100 pF
11
RF Port 2
10
9
×
×
8
×
330 pF
S2244
Figure 3. SKY12338-337LF Example of Externally Floated 2-Bit Attenuator
This technique allows a larger value floating capacitor
to be used than what is practical to include on the
attenuator die to float the attenuator above ground
potential. Adding large value DC blocking capacitors to
the RF input and output allows the gates of the FETs to be
biased directly with positive voltage and is a good option
for single bit or low bit count attenuators that do not
require complicated biasing. One limitation to this design
technique is that the usable bandwidth is somewhat
reduced since the impedance of the blocking capacitors is
composed of capacitive reactance as well as the reactance
of the capacitors’ parasitic inductance, thus making
resonances possible. For RF applications, the value of the
floating capacitors is much lower and so it is practical to
incorporate them onto the GaAs die. (See Figure 4).
Capacitors
DTS
STD
STD
Some attenuators also contain a CMOS decoder/driver die
which may perform several functions. (See Figure 2).
STD
Figure 4. Capacitors Incorporated onto the Die for RF Applications.
(SKY12338-337LF)
By including the floating caps on die, the only additional
inductance added to the RF ground path is the bond wire
from the chip to the exposed paddle of the QFN package.
Typical capacitor values commonly used in this manner
limit the lower frequency response of the attenuator to
approximately 600–700 MHz. Making the capacitors
larger in value adds significantly to the size of the chip,
which increases cost.
Skyworks’ portfolio of attenuators includes single bit
devices up to a fully integrated designs with 7 bits. The
7 bit attenuator provides discrete 0.25 dB steps up
to 31.75 dB. For applications requiring more dynamic
range, higher total attenuation can be achieved by
placing attenuators in cascade. In these high dynamic
range applications, the use of two separate packaged
attenuators is the best way to achieve higher levels
of attenuation. In such cascades, it can be difficult to
maintain monotonicity over very large dynamic ranges
and broad bandwidths. Good step size monotonicity is
more realizable if the LSB is 1 dB and IF the bandwidth is
narrow. An example of a cascaded architecture is shown
in Figure 5. This combines a 5 bit digital attenuator with
a single bit attenuator to achieve 63 dB of potential
dynamic range.
NC/GND
V1
5
4
32
V2
6
V1
2
3
CBL
CBP
CBL
J1
RF1
J2
RF
GND
RF2
8 dB
V2
V4
16 dB
V3
V5
1
1 dB
2 dB
4 dB
Figure 5. Multiple Attenuators Cascaded to Increase Dynamic Range (SKY12339-350LF cascaded with AA104-73LF).
Green Initiative™
Through our Green Initiative,™ we are committed to manufacturing products that comply with global
government directives and industry requirements.
Skyworks is continuously innovating RF, analog, and mixed-signal ICs. For the latest product introductions and
information about Skyworks, visit our Web site at www.skyworksinc.com
For additional information on our broad overall product portfolio, please contact your local sales office or email us at
[email protected]
Skyworks Solutions, Inc.
20 Sylvan Road, Woburn, MA 01801
USA: (781) 376-3000 • Asia: 886 2 2735 0399
Europe: 33 (0)1 43548540 • Fax: (781) 376-3100
Email: [email protected] • www.skyworksinc.com
BRO393-12B 9/12
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