DATA SHEET
SKY12345-362LF: 0.7-4.0 GHz Five-Bit Digital Attenuator
with Serial-to-Parallel Driver (0.5 dB LSB)
Applications
•
Base stations
•
Wireless and RF data
•
Wireless local loop gain control circuits
Features
•
Broadband operation: 0.7 to 4.0 GHz
•
Attenuation: 15.5 dB
•
LSB attenuation: 0.5 dB
•
Low insertion loss: 1 dB @ 900 MHz
•
Positive voltage operation: 5 V
•
Integrated silicon serial-to-parallel driver
•
Small, QFN
(24-pin,
4 x 4 mm) package (MSL1, 260
°C
per
JEDEC J-STD-020)
Figure 1. SKY12345-362LF Block Diagram
Description
The SKY12345-362LF is a GaAs FET five-bit digital attenuator I/C
with a serial-to-parallel driver. The device
is
provided in a
4 x 4
mm,
24-pin Quad Flat No-Lead (QFN) package.
The SKY12345-362LF is particularly suited for applications
in
which high attenuation accuracy, low insertion loss, and low
intermodulation products are required.
A functional block diagram is shown in Figure 1. The pin
configuration and package are shown in Figure 2. Signal pin
assignments and functional pin descriptions are provided in
Table 1.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201136C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2011
1
DATA SHEET • SKY12345-362LF FIVE-BIT DIGITAL ATTENUATOR
Figure 2. SKY12345-362LF Pinout – 24-Pin QFN
(Top View)
Table 1. SKY12345-362LF Signal Descriptions
Pin #
1
2
3
4
5
6
7
8
9
RF1
GND or N/C
GND or N/C
SERIAL_OUTPUT
GND or N/C
RESET
CLOCK
LATCH_ENABLE
Name
GND or N/C
Description
Ground or no connection
RF input/output. Must be DC blocked.
Ground or no connection
Ground or no connection
Data output delayed by eight clock cycles
Ground or no connection
Reset. Clears shift registers.
Serial clock input
On rising edge of pulse, shifts five most
recent clocked-in bits to set attenuation
state
Ground or no connection
Data input
Ground or no connection
Pin #
13
14
15
16
17
18
19
20
21
VCC
GND or N/C
GND or N/C
RF2
GND or N/C
GND
GND
GND
Name
GND or N/C
Description
Ground or no connection
Fixed bias for SPI
Ground or no connection
Ground or no connection
RF input/output. Must be DC blocked.
Ground or no connection
Ground
Ground
Ground
10
11
12
Note:
GND or N/C
SERIAL_INPUT
GND or N/C
22
23
24
GND
GND
GND
Ground
Ground
Ground
Exposed pad must be grounded.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
2
January 11, 2011 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201136C
DATA SHEET • SKY12345-362LF FIVE-BIT DIGITAL ATTENUATOR
Functional Description
The SKY12345-362LF is a five bit digital attenuator comprised of
a GaAs attenuator and a silicon CMOS driver. The attenuation
setting is controlled by a serial-to-parallel interface. Attenuation is
set by a stream of data that is clocked into the shift registers of
the silicon chip by the clock signal. To set the attenuation state, a
latch signal is sent to the appropriate pin to send the correct bias
voltages to the GaAs attenuator.
More than one attenuator can be cascaded together and the data
may be passed through one device to the other using the
SERIAL_OUTPUT signal (pin 5). To reset the attenuator to the
insertion loss state, a logic low signal may be sent to the RESET
pin. DC bias voltage to the silicon CMOS chip is applied to pin 14
(VCC).
Power-Up/Power-Down Timing
Serial input data (SERIAL_INPUT pin) is shifted into the register on
the rising edge of the clock (CLOCK pin), least significant bit (LSB)
first. The attenuator changes states on the rising edge of the
latch-enable (LATCH_ENABLE pin) signal, according to the most
recent five bits of shifted data accepted since the previous falling
edge of the latch enable signal. The serial data output is the serial
input data delayed by eight clock cycldes.
Refer to the timing diagram in Figure 3 and timing parameter
specifications in Table 2. Table 3 shows the transition states
based on the latch enable, clock, and reset logic settings.
Power-up sequence is as follows:
0. Connect ground
1. Apply V
CC
2. Set all inputs (SCK, SDA, LE)
The power-down sequence is the reverse of above.
Figure 4 shows an example of how to set the attenuator to the
0.5 dB state. The progression of the bit states vs the clock signal
is shown. The timing diagram shows that when the latch enable
signal goes high, the voltages v1 to v5 set the attenuator to the
0.5 dB state.
Electrical and Mechanical Specifications
The absolute maximum ratings of the SKY12345-362LF are
provided in Table 4.
Electrical
specifications are provided in
Tables 5 and 6.
Typical performance characteristics of the SKY12345-362LF are
illustrated in Figures 5 through 11.
The state of the SKY12345-362LF is determined by the logic
provided in Table 7.
Figure 3. Power-Up/Power-Down Timing
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201136C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2011
3
DATA SHEET • SKY12345-362LF FIVE-BIT DIGITAL ATTENUATOR
Table 2. Power-Up/Power-Down Timing Parameters
Parameter
Serial input setup time
Hold time from serial input to shift clock
Setup time from shift clock to latch enable
Propagation delay, latch enable to C0.5
through C8
Setup time from reset to shift clock
Clock frequency
Symbol
ts
th
tlsup
tpd
–
f
CLK
20
30
40
30
50
10
V
CC
= 5 V
Minimum
Typical
5
5
100
70
Maximum
Minimum
V
CC
= 3 V
Typical
5
5
Maximum
Units
ns
ns
ns
ns
ns
MHz
Table 3. Transition State Logic
LATCH_ENABLE (Pin 9)
X
X
X
CLOCK (Pin 8)
X
RESET (Pin 7)
L
H
H
Shift register cleared
Shift register clocked
Contents of shift register transferred to digital attenuator
Function
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
4
January 11, 2011 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201136C
DATA SHEET • SKY12345-362LF FIVE-BIT DIGITAL ATTENUATOR
Figure 4. Example for Setting 0.5 dB State
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201136C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2011
5
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