DATA SHEET
SKY74068-21: Dual-Band Transmitter for CDMA and PCS
Femtocell Applications
Applications
Dual-band femtocells
Description
The SKY74068-21 transmitter is a highly integrated device for
dual-band Code Division Multiple Access (CDMA) femtocells. The
SKY74068-21 supports femtocells in the cellular CDMA and
Personal Communications System (PCS) modes.
The device requires a minimum number of external components
to complete a CDMA radio subsystem. Included on-chip are the
baseband filter, direct upconversion In-Phase and Quadrature (I/Q)
mixers, variable gain power amplifier (PA) drivers, a fully
integrated Voltage Controlled Oscillator (VCO) with Local Oscillator
(LO) generation blocks, and a dual-mode fractional-N/integer-N
Phase Locked Loop (PLL).
External components needed for operation include bias resistors,
bypass capacitors, and passives to comprise the PLL loop filter.
The signal enters the chip as an analog baseband I/Q signal. It is
filtered by the baseband filter and upconverted to the desired RF
transmit frequency. The signal is amplified by one of two
upconverters, depending on whether the chip is operating in
cellular or PCS mode. The resulting signal is fed through the
appropriate PA driver stage to provide variable output power and
to drive the external PA. The signal is then filtered by an external
Surface Acoustic Wave (SAW) filter and sent to the PA to obtain
the final rated power.
The 32-pin RF Land Grid Array (RFLGA) device package and
pinout are shown in Figure 1. Figure 2 shows a functional block
diagram for the SKY74068-21.
Features
Low power consumption in all operating modes
Direct upconversion architecture
Device controlled using a three-wire read/write serial bus
interface with independent supply voltage
Baseband RC filter to reject receive band noise
Fully integrated VCO with auto-tuning
Dual-mode fractional-N/integer-N PLL
Variable gain PA drivers
Differential cellular driver output matched to 200
Single-ended PCS driver output matched to 50
Transmit power control with >75 dB dynamic range
Low current consumption at low transmit power minimizes
current consumption and noise
Hardware TX_ENABLE for gated mode operation
RFLGA™ (32-pin, 5 x 5 x 1 mm) package with downset paddle
(MSL3, 260
C
per JEDEC J-STD-020)
Skyworks offers lead (Pb)-free, RoHS (Restriction of
Hazardous Substances) compliant packaging.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
200761B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 2, 2010
1
DATA SHEET • SKY74068-21 CDMA TRANSMITTER
VCC_CLK
REF
Q+
27
Q–
32
31
30
29
28
26
25
24
23
22
21
20
19
18
17
LD_OUT
VCC_PLL_1
N/C
CP
VCC_PLL_2
VCO_IO
VCO_TUNE
VCO_EXT_RES
VCO_BYPASS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
CS
I+
I–
BIAS_RES
VCC_RF_4
VCC_RF_3
PCS_OUT
VCC_RF_2
CELL_OUT–
CELL_OUT+
TX_ENABLE
VCC_RF_1
VCC_VCO_CORE
VCC_LD
VCC_INTERFACE
LATCH_ENABLE
GAIN_CTRL
CLK
DATA
S1157
Figure 1. SKY74068-21 Transmitter Pinout – 32-Pin RFLGA (5 x 5 mm)
(Top View)
REF
LD_OUT
Fractional-N/
Integer-N PLL
CP
0
O
Q–
Q+
I–
I+
PCS_OUT
90
O
LO Generation
VCO_IO
90
O
CELL_OUT–
Serial I/O
Integrated
VCO Tank
0
O
CELL_OUT+
LATCH_ENABLE
GAIN_CTRL
CLK
DATA
S347
Figure 2. SKY74068-21 Transmitter Block Diagram
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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August 2, 2010 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 200761B
DATA SHEET • SKY74068-21 CDMA TRANSMITTER
Technical Description
Baseband Filter
The SKY74068-21 has two modes of operation: current and
voltage. In current mode, the device consists of a low resistive
input. Together with an external capacitor across the differential
inputs, the low resistive input acts as a low-pass filter.
In voltage mode operation, the baseband section of the
SKY74068-21 contains a simple RC filter to reject receive band
noise from incoming I and Q signals.
VCO, LO Chain, and PLL
The VCO has an internal tank circuit automatically tuned to the
desired frequency. The VCO is connected to an on-chip PLL and
LO generation blocks. The output of the LO generation blocks
drives the LO port of the I/Q RF upconverter.
A dual-mode fractional-N/integer-N PLL is used to lock the VCO to
the desired frequency in CDMA mode. A bi-directional buffer is
available to measure the VCO output or to enable use of an
external LO for testing purposes.
I/Q RF Upconverter
The I/Q RF upconverter converts the incoming I/Q signal to the
desired RF output signal. The upconverter passes the output
signal directly to the variable gain PA drivers. The LO for the
upconverter is provided by the VCO and LO generation blocks.
The upconverter block consists of two separate mixers, one for
cellular mode operation and the other for PCS mode. The output
of the PCS mixer is routed to the PCS PA driver and the cellular
mixer output is routed to the cellular PA driver.
Variable Gain PA Drivers
The SKY74068-21 includes two PA drivers. These drivers control
the power level of the signal provided by the PCS and cellular
upconverters. The gain of both drivers is variable, yielding over
75 dB of dynamic range.
The PCS driver output is single-ended, while the cellular driver is
differential. Both are open collector outputs that require external
matching.
Serial Bus Interface
A three-wire serial bus with read/write capability provides mode
and bias control, and control of the PLL. The serial interface
consists of three signals: a bus clock (CLK), a bus enable
(LATCH_ENABLE), and the serial, bi-directional data line (DATA).
Package and Handling Information
Since the device package is sensitive to moisture absorption, it is
baked and vacuum packed before shipping. Instructions on the
shipping container label regarding exposure to moisture after the
container seal is broken must be followed. Otherwise, problems
related to moisture absorption may occur when the part is
subjected to high temperature during solder assembly.
The SKY74068-21 is rated to Moisture Sensitivity Level 3 (MSL3)
at 260
C.
It can be used for lead or lead-free soldering. For
additional information, refer to the Skyworks Application Note,
PCB Design & SMT Assembly/Rework Guidelines for RFLGA
Packages,
document number 103147.
Care must be taken when attaching this product, whether it is
done manually or in a production solder reflow environment.
Production quantities of this product are shipped in a standard
tape and reel format.
Electrical and Mechanical Specifications
Signal pin assignments and functional pin descriptions are
described in Table 1. The absolute maximum ratings of the
SKY74068-21 are provided in Table 2. The recommended
operating conditions are specified in Table 3 and electrical
specifications are provided in Table 4.
An application schematic diagram for the SKY74068-21 is shown
in Figure 3. The package dimensions for the 32-pin RFLGA are
shown in Figure 4, and the tape and reel dimensions are provided
in Figure 5.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
200761B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 2, 2010
3
DATA SHEET • SKY74068-21 CDMA TRANSMITTER
Table 1. SKY74068-21 Signal Descriptions
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
LD_OUT
VCC_PLL_1
N/C
CP
VCC_PLL_2
VCO_IO
VCO_TUNE
VCO_EXT_RES
VCO_BYPASS
VCC_VCO_CORE
VCC_LO
VCC_INTERFACE
CLK
LATCH_ENABLE
DATA
GAIN_CTRL
Name
Description
Lock detect output. Open drain.
Supply for the PLL.
No connection
Charge pump output.
Supply for the PLL.
Input/output port for the VCO bi-
directional buffer.
Loop filter input for the VCO.
External bias-setting resistor for the VCO.
External capacitor for VCO noise filtering.
Supply for the VCO.
Supply for LO generation blocks.
Supply for serial bus.
Clock signal for serial bus.
Latch enable signal for serial bus.
Data signal for serial bus.
Gain control voltage.
Pin #
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Name
VCC_RF_1
TX_ENABLE
CELL_OUT+
CELL_OUT–
VCC_RF_2
PCS_OUT
VCC_RF_3
VCC_RF_4
BIAS_RES
CS
Q+
Q–
I+
I–
VCC_CLK
REF
Description
Supply for bias circuits of all drivers.
Transmit enable/disable pin for all blocks,
excluding VCO and PLLs.
Positive cellular driver differential output.
Negative cellular driver differential output.
Supply for PCS and cellular output drivers.
PCS driver output.
Supply for bias circuits of the PCS
differential driver.
Supply for the mixer and associated bias
blocks.
External bias resistor for all blocks,
excluding VCO.
Current sink.
Positive quadrature analog baseband
input.
Negative quadrature analog baseband
input.
Positive in-phase analog baseband input.
Negative in-phase analog baseband input.
Supply for the TCXO buffer.
TCXO input.
Table 2. SKY74068-21 Absolute Maximum Ratings
Parameter
Supply voltage (VCC)
Input voltage range
Storage temperature
Ambient operating temperature
Note:
Symbol
Minimum
–0.3
–0.3
–40
–30
Typical
Maximum
+3.6
VCC
+125
+85
Units
V
V
C
C
Exposure to maximum rating conditions for extended periods may reduce device reliability. There is no damage to device with only one parameter set at the limit and all other
parameters set at or below their nominal value.
CAUTION:
Although this device is designed to be as robust as possible, Electrostatic Discharge (ESD) can damage this device. This device
must be protected at all times from ESD. Static charges may easily produce potentials of several kilovolts on the human body
or equipment, which can discharge without detection. Industry-standard ESD precautions should be used at all times.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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August 2, 2010 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 200761B
DATA SHEET • SKY74068-21 CDMA TRANSMITTER
Table 3. SKY74068-21 Recommended Operating Conditions
Parameter
Supply voltage
Logic level:
high
low
Z
IN
of logic control inputs
Supply current:
CDMA mode @ 5 dBm
PCS mode @ 5 dBm
Supply current in sleep mode
Symbol
Minimum
2.70
VCC – 0.5
0
50
71
76
100
Typical
2.85
Maximum
3.00
VCC
0.5
Units
V
V
V
k
mA
mA
A
Table 4. SKY74068-21 Electrical Specifications (Note 1) (1 of 3)
(T
A
= +25
C,
VCC = 2.85 V, CDMA2000 Waveform Used Unless Otherwise Noted)
Parameter
Baseband Filter
Cutoff frequency
Amplitude ripple
Amplitude imbalance between I and Q
chains
Phase imbalance between I and Q chains
Rejection:
@ 45 MHz (CDMA)
@ 80 MHz (PCS)
I/Q RF Upconverter, Voltage Mode
Input signal level
Input common mode voltage
Input impedance
I/Q Upconverter, Current Mode
Input signal level
Current sink
I/Q RF Upconverter and Driver, CDMA
I/Q frequency range
–1 dB bandwidth
RF output frequency range
Maximum RF output power
Dynamic range
Control voltage range
Slope of RF AGC
ACPR:
750 kHz offset @ +4 dBm
1.98 MHz offset @ +0 dBm
75
0.2
30
50
–55
–70
2.7
75
800
0.63
5
836
+5
950
2.5
MHz
MHz
MHz
dBm
dB
V
dB/V
dBc
dBc
20
1
0.6
200
mA
A
1.3
1
1.5
50
1.9
Vp-p
differential
V
k
3
0.5
0.20
1
20
25
0.25
MHz
dB
dB
degrees
dB
dB
Symbol
Test Condition
Min
Typical
Max
Units
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
200761B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 2, 2010
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