Skyworks CX77304-17 Cx77304-17 pa module for tri-band egsm dcs pcs / gpr Datasheet

DATA SHEET
CX77304-17 PA Module for Tri-band EGSM DCS PCS / GPRS
Applications
Description
• Tri-band cellular handsets
encompassing
- Class 4 EGSM900
- Class 1 DCS1800
- PCS1900, and
- Up to Class 10 GPRS
multi-slot operation
The CX77304-17 Power Amplifier Module (PAM) is designed in a compact form factor for tri-band
cellular handsets comprising EGSM900, DCS1800, and PCS1900 operation. It also supports Class 10
General Packet Radio Service (GPRS) multi-slot operation.
Features
• High efficiency
- EGSM 55%
- DCS 50%
- PCS 45%
• Input/output matching
- 50 Ω internal
• Small outline
- 9.1 mm × 11.6 mm
• Low profile
- 1.5 mm
• Low APC current
- 10 µA typical
The PAM consists of an EGSM900 PA block, a DCS1800/PCS1900 PA block, impedancematching circuitry for 50 Ω input and output, and bias control circuitry. Two separate Heterojunction
Bipolar Transistor (HBT) PA blocks are fabricated on a single Gallium Arsenide (GaAs) die. One PA
block operates in the EGSM900 band and the other PA block supports both the DCS1800 and the
PCS1900 bands. Optimized for lithium ion battery operation, both PA blocks share common power
supply pins to distribute current. A custom CMOS integrated circuit provides the internal interface
circuitry, including a current amplifier that minimizes the required power control current (IAPC) to 10
µA, typical. The GaAs die, the Silicon (Si) die, and passive components are mounted on a multi-layer
laminate substrate. The assembly is encapsulated with plastic overmold.
The RF input and output ports are internally matched to 50 Ω to reduce the number of external
components for a tri-band design. Extremely low leakage current (2 µA, typical) of the dual PA module
maximizes handset standby time. The CX77304-17 also contains band-select switching circuitry to
select EGSM (logic 0) and DCS/PCS (logic 1) as determined from the Band Select (BS) signal. In
the block diagram shown below, the BS pin selects the PA output (DCS/PCS OUT or EGSM OUT) while
the Analog Power Control (APC) controls the level of output power.
• Gold plated, lead-free
contacts
Figure 1. Functional Block Diagram
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DATA SHEET • CX77304-17
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Electrical Specifications
The CX77304-17 is a static-sensitive electronic device and should
not be stored or operated near strong electrostatic fields. Detailed
ESD precautions along with information on device dimensions, pin
descriptions, packaging and handling can be found in later
sections of this data sheet.
The following tables list the electrical characteristics of the
CX77304-17 Power Amplifier. Table 1 lists the absolute maximum
ratings and Table 2 shows the recommended operating
conditions. Table 3 shows the electrical characteristics of the
CX77304-17 for EGSM, DCS, and PCS modes. A typical
CX77304-17 application diagram appears in Figure 2.
Table 1. Absolute Maximum Ratings
Parameter
Minimum
Maximum
Unit
—
15
dBm
Input Power (PIN)
Supply Voltage (VCC), Standby, VAPC ≤ 0.3 V
—
7
V
Control Voltage (VAPC)
–0.5
VCC_MAX – 0.2 (See Table 3)
V
Storage Temperature
–55
+100
°C
Table 2. Recommended Operating Conditions (1)
Parameter
Minimum
Typical
Maximum
3.5
4.8 (1)
V
A
Supply Voltage (VCC)
2.9
Supply Current (ICC)
0.0
2.5 (1)
Operating Case Temperature (TCASE)
1-Slot (12.5% duty cycle)
2-Slot (25% duty cycle)
3-Slot (37.5% duty cycle)
4-Slot ( 50% duty cycle)
–20
–20
–20
–20
100
90
75
60
(1) For charging conditions with VCC > 4.8 V, derate ICC linearly down to 0.5 A max at VCC = 5.5 V.
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Unit
°C
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
DATA SHEET • CX77304-17
Table 3. CX77304-17 Electrical Specifications (1) (1 of 6)
General
Parameter
Symbol
Supply voltage
VCC
Power control current
lAPC
Test Condition
Minimum
Typical
Maximum
Units
—
2.9
3.5
4.8
V
—
—
10
100
µA
—
—
5
µA
200
—
600
mV
8
µs
Units
VCC = 4.5 V
VAPC = 0.3 V
TCASE = +25 °C
PIN ≤ –60 dBm
Leakage Current
IQ
APC Enable Threshold
VAPC_TH
APC Enable Switching Delay
tSW
—
Time from VAPC ≥ VAPC_TH until
POUT ≤ (POUT_FINAL – 3 dB)
5
EGSM900 Mode (f = 880 to 915 MHz and PIN = 7 to 12 dBm)
Parameter
Symbol
Test Condition
Minimum
Typical
Maximum
Frequency range
f
—
880
—
915
MHz
Input power
PIN
—
7
—
12
dBm
Analog power control voltage
VAPC
POUT = 32 dBm
1.2
1.7
2.1
V
PAE
VCC = 3.5 V
POUT ≥ 34.5 dBm
VAPC ≈ 2.0 V
pulse width 577 µs
duty cycle 1:8
TCASE = +25 °C
50
55
—
PAE_LOW INPUT
VCC = 3.5 V
POUT ≥ 34.5 dBm
VAPC ≈ 2.0 V
pulse width 577 µs
duty cycle 1:8
TCASE = +25 °C
PIN = 4 dBm
—
52
—
2f0 to 13f0
BW = 3 MHz
5 dBm ≤ POUT ≤ 35 dBm
—
—
–7
POUT
VCC = 3.5 V
VAPC ≈ 2.0 V
TCASE = +25 °C
34.5
35.0
—
POUT_MAX
VCC = 3.5 V
VAPC ≈ 2.0 V
TCASE = +25 °C
PIN = 4 dBm
—
34.75
—
POUT_MAX
VCC = 2.9 V
VAPC ≤ 2.6 V
TCASE = –20 °C to +100 °C
(See Table 2 for multislot)
PIN = 7 dBm
32.0
33.0
—
POUT_MAX
VCC = 4.8 V
VAPC ≤ 2.6 V
TCASE = –20 °C to +100 °C
(See Table 2 for multislot)
PIN = 7 dBm
32.0
33.0
—
Power Added Efficiency
Harmonics
2nd to 13th
Output power
%
dBm
dBm
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DATA SHEET • CX77304-17
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Table 3. CX77304-17 Electrical Specifications (1) (2 of 6)
EGSM900 Mode (f = 880 to 915 MHz and PIN = 7 to 12 dBm) [continued]
Parameter
Symbol
Test Condition
Minimum
Typical
Maximum
Units
Input VSWR
ΓIN
POUT = 5 to 35 dBm
controlled by VAPC
—
1.5:1
2:1
—
Forward isolation
POUT_STANDBY
PIN = 12 dBm
VAPC = 0.3 V
—
–35
–30
dBm
Time from POUT = –10 dBm toPOUT = +5 dBm
τ ≈ 90%
—
5
8
Time from POUT = –10 dBm to POUT = +20 dBm
τ ≈ 90%
—
5
8
Time from POUT = –10 dBm to POUT = +34.5 dBm
τ ≈ 90%
—
2
4
τRISE, τFALL
Switching time
Spurious
Load mismatch
Noise power
Spur
All combinations of the following parameters:
VAPC = controlled (2)
PIN = min. to max.
VCC = 2.9 V to 4.8 V
Load VSWR = 8:1, all phase angles
No parasitic oscillation > –36 dBm
Load
All combinations of the following parameters:
VAPC = controlled (2)
PIN = min. to max.
VCC = 2.9 V to 4.8 V
Load VSWR = 10:1, all phase angles
No module damage or permanent degradation
PNOISE
At f0 + 20 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 34.5 dBm
—
—
–82
At f0 + 10 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 34.5 dBm
—
—
–76
At 1805 to 1880 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 34.5 dBm
—
—
–90
—
6
9
—
–25
–20
—
–18
–15
f0
Coupling of 2nd and 3rd harmonic from the EGSM
band into the DCS / PCS band
2f0
3f0
Measured at the DCS output
–15 dBm ≤ POUT ≤ 34 dBm
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µs
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dBm
dBm
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
DATA SHEET • CX77304-17
Table 3. CX77304-17 Electrical Specifications (1) (3 of 6)
DCS1800 Mode (f = 1710 to 1785 MHz and PIN = 6 to 11 dBm)
Parameter
Symbol
Frequency range
Test Condition
Minimum
Typical
Maximum
Units
—
1710
—
1785
MHz
f
Input power
PIN
Analog power control voltage
VAPC
POUT = 29.5 dBm
PAE
VCC = 3.5 V
POUT ≥ 32 dBm
VAPC ≈ 2.0 V
pulse width 577 µs
duty cycle 1:8
TCASE = +25 °C
PAE_LOW INPUT
VCC = 3.5 V
POUT ≥ 32 dBm
VAPC ≈ 2.0 V
pulse width 577 µs
duty cycle 1:8
TCASE = +25 °C
PIN = 4 dBm
Power Added Efficiency
2nd
2f0
3rd to 7th
3f0 to 7f0
Harmonics
—
BW = 3 MHz
5 dBm ≤ POUT ≤ 32 dBm
0 °C ≤ TCASE ≤ +90 °C
2.9 V ≤ VCC ≤ 4.0 V
6
—
11
dBm
1.35
1.7
2.1
V
45
50
—
%
—
49
—
—
—
–5
—
—
–7
dBm
POUT
VCC = 3.5 V
VAPC ≈ 2.0 V
TCASE = +25 °C
32.0
32.5
—
POUT_MAX
VCC = 3.5 V
VAPC ≈ 2.0 V
TCASE = +25 °C
PIN = 4 dBm
—
32.1
—
POUT_MAX
VCC = 2.9 V
VAPC ≤ 2.6 V
TCASE = –20 °C to +100 °C
(See Table 2 for multislot)
PIN = 6 dBm
29.5
30.5
—
POUT_MAX
VCC = 4.8 V
VAPC ≤ 2.6 V
TCASE = –20 °C to +100 °C
(See Table 2 for multislot)
PIN = 6 dBm
29.5
30.5
—
Output power
dBm
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DATA SHEET • CX77304-17
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Table 3. CX77304-17 Electrical Specifications (1) (4 of 6)
DCS1800 Mode (f = 1710 to 1785 MHz and PIN = 6 to 11 dBm) [continued]
Parameter
Symbol
Test Condition
Minimum
Typical
Maximum
Units
Input VSWR
ΓIN
POUT = 0 to 32 dBm
controlled by VAPC
—
—
2:1
—
Forward isolation
POUT_STANDBY
PIN = 10 dBm
VAPC = 0.3 V
—
–40
–35
dBm
Time from POUT = –10 dBm to POUT = 0 dBm
τ ≈ 90%
—
10
12
Time from POUT = –10 dBm to POUT = +20 dBm
τ ≈ 90%
—
5
8
Time from POUT = –10 dBm to POUT = +32 dBm
τ ≈ 90%
—
2
5
Switching time
Spurious
Load mismatch
Noise power
τRISE, τFALL
Spur
All combinations of the following parameters:
VAPC = controlled (3)
PIN = min. to max.
VCC = 2.9 V to 4.8 V
Load VSWR = 8:1, all phase angles
No parasitic oscillation > –36 dBm
Load
All combinations of the following parameters:
VAPC = controlled (3)
PIN = min. to max.
VCC = 2.9 V to 4.8 V
Load VSWR = 10:1, all phase angles
No module damage or permanent degradation
PNOISE
At f0 + 20 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 32 dBm
—
At 925 to 960 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 32 dBm
—
—
–80
dBm
—
–95
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PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
DATA SHEET • CX77304-17
Table 3. CX77304-17 Electrical Specifications (1) (5 of 6)
PCS1900 Mode (f = 1850 to 1910 MHz and PIN = 6 to 11 dBm)
Parameter
Symbol
Frequency range
Test Condition
Minimum
Typical
Maximum
Units
—
1850
—
1910
MHz
f
Input power
PIN
Analog power control voltage
VAPC
POUT = 29.5 dBm
PAE
VCC = 3.5 V
POUT ≥ 32 dBm
VAPC ≈ 2.0 V
pulse width 577 µs
duty cycle 1:8
TCASE = +25 °C
PAE_LOW INPUT
VCC = 3.5 V
POUT ≥ 32 dBm
VAPC ≈ 2.0 V
pulse width 577 µs
duty cycle 1:8
TCASE = +25 °C
PIN = 4 dBm
—
44.5
—
2f0 to 7f0
BW = 3 MHz
5 dBm ≤ POUT ≤ 32 dBm
—
—
–7
POUT
VCC = 3.5 V
VAPC ≈ 2.0 V
TCASE = +25 °C
32.0
32.5
—
POUT_MAX
VCC = 3.5 V
VAPC ≈ 2.0 V
TCASE = +25 °C
PIN = 4 dBm
—
32.3
—
POUT_MAX
VCC = 2.9 V
VAPC ≤ 2.6 V
TCASE = –20 °C to +100 °C
(See Table 2 for multislot)
PIN = 6 dBm
29.5
30.5
—
POUT_MAX
VCC = 4.8 V,
VAPC ≤ 2.6 V
TCASE = –20 °C to +100 °C
(See Table 2 for multislot)
PIN = 6 dBm
29.5
30.5
—
Input VSWR
ΓIN
POUT = 0 to 32 dBm
controlled by VAPC
—
—
2.2:1
—
Forward isolation
POUT_STANDBY
PIN = 10 dBm
VAPC = 0.3 V
—
–40
–35
dBm
Time from POUT = –10 dBm to POUT = 0 dBm
τ ≈ 90%
—
10
12
Time from POUT = –10 dBm to POUT = +20 dBm
τ ≈ 90%
—
5
8
Time from POUT = –10 dBm to POUT = +32 dBm
τ ≈ 90%
—
2
5
Power Added Efficiency
Harmonic
2nd to 7th
Output power
Switching time
τRISE, τFALL
—
6
—
11
dBm
1.35
1.7
2.1
V
45
50
—
%
dBm
dBm
µs
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DATA SHEET • CX77304-17
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Table 3. CX77304-17 Electrical Specifications (1) (6 of 6)
PCS1900 Mode (f = 1850 to 1910 MHz and PIN = 6 to 11 dBm) [continued]
Parameter
Spurious
Load mismatch
Noise power
Symbol
Test Condition
Minimum
Typical
Maximum
Units
Spur
All combinations of the following parameters:
VAPC = controlled (3)
PIN = min. to max.
VCC = 2.9 V to 4.8 V
Load VSWR = 8:1, all phase angles
No parasitic oscillation > –36 dBm
Load
All combinations of the following parameters:
VAPC = controlled (3)
PIN = min. to max.
VCC = 2.9 V to 4.8 V
Load VSWR = 10:1, all phase angles
No module damage or permanent degradation
PNOISE
At f0 + 20 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 32 dBm
—
At 869 to 894 MHz
RBW = 100 kHz
VCC = 3.5 V
5 dBm ≤ POUT ≤ 32 dBm
—
—
–77
dBm
—
–95
(1) Unless specified otherwise: TCASE = –20 °C to max. operating temperature (see Table 2), RL = 50 Ω, pulsed operation with pulse width ≤ 2308 µs and duty cycle ≤ 4:8, VCC = 2.9 V to 4.8 V.
(2) ICC = 0A to xA, where x = current at POUT = 34.5 dBm, 50 Ω load, and VCC = 3.5 V.
(3) ICC = 0A to xA, where x = current at POUT = 32.0 dBm, 50 Ω load, and VCC = 3.5 V.
Figure 2. Typical CX77304-17 PAM Application
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PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Package Dimensions and Pin Descriptions
Figure 3 is a mechanical diagram of the pad layout for the 16-pin
leadless CX77304-17 tri-band PA module. Figure 4 provides a
recommended phone board footprint for the PAM to help the
designer attain optimum thermal conductivity, good grounding,
and minimum RF discontinuity for the 50-ohm terminals.
DATA SHEET • CX77304-17
Table 4 lists the pin labels and descriptions and Figure 5 shows
the device pin configuration and pin numbering, which starts with
pin 1 in the upper left, as shown, and increments counterclockwise around the package. Figure 6 interprets typical case
markings.
Figure 3. CX77304-17 PAM Package Dimensions—16-pin Module (All Views)
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DATA SHEET • CX77304-17
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Figure 4. Phone Board Layout Footprint for 9.1 mm x 11.6 mm Package
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PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
DATA SHEET • CX77304-17
Table 4. CX77304-17 Signal Description
Pin
Name
Description
Ground
Pin
GND
2
DCS/PCS_IN
RF input to DCS/PCS PA
10
EGSM_OUT
EGSM RF output (DC coupled)
3
GND
Ground
11
GND
Ground
4
EGSM_IN
RF input to EGSM PA
12
DCS/PCS_OUT
DCS/PCS RF output (DC coupled)
5
GND
Ground
13
GND
Ground
6
VCC1
Power supply for PA driver stages
14
APC
Analog Power Control
7
GND
Ground
15
GND
Ground
8
VCC2
Power supply for PA output stages
16
BS
Band Select
Package and Handling Information
Because of its sensitivity to moisture absorption, this device
package is baked and vacuum packed prior to shipment.
Instructions on the shipping container label must be followed
regarding exposure to moisture after the container seal is broken,
otherwise, problems related to moisture absorption may occur
when the part is subjected to high temperature during solder
assembly.
The CX77304-17 is capable of withstanding an MSL 3/240 °C
solder reflow. Care must be taken when attaching this product,
whether it is done manually or in a production solder reflow
environment. If the part is attached in a reflow oven, the
temperature ramp rate should not exceed 5 °C per second;
maximum temperature should not exceed 240 °C. If the part is
manually attached, precaution should be taken to insure that the
part is not subjected to temperatures exceeding 240 °C for more
than 10 seconds. For details on both attachment techniques,
precautions, and handling procedures recommended by
Skyworks, please refer to Skyworks Application Note: PCB Design
and SMT Assembly/Rework, Document Number 101752.
GND
Description
1
Figure 5. CX77304-17 Pin Configuration—16-Pin Leadless PAM
(Top View)
9
Name
Ground
Figure 6. Typical Case Markings
Additional information on standard SMT reflow profiles can also
be found in the JEDEC Standard J–STD–020.
Production quantities of this product are shipped in the standard
tape-and-reel format. For packaging details, refer to Skyworks
Application Note: Tape and Reel, Document Number 101568.
Electrostatic Discharge Sensitivity
The CX77304-17 is a Class I device. Figure 7 lists the
Electrostatic Discharge (ESD) immunity level for each pin of the
CX77304-17 product. The numbers in Figure 7 specify the ESD
threshold level for each pin where the I-V curve between the pin
and ground starts to show degradation. The ESD testing was
performed in compliance with MIL-STD-883E Method 3015.7
using the Human Body Model. If ESD damage threshold
magnitude is found to consistently exceed 2000 volts on a given
pin, this so is indicated. If ESD damage threshold below 2000
volts is measured for either polarity, numbers are indicated that
represent worst case values observed in product characterization.
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DATA SHEET • CX77304-17
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
Technical Information
CMOS Bias Controller Characteristics
The CMOS die within the PAM performs several functions that are
important to the overall module performance. Some of these
functions must be considered for development of the power
ramping features in a 3GPP compliant transmitter power control
loop. Power ramping considerations will be discussed later in this
section.
NOTE: Please refer to 3GPP TS 05.05, Digital Cellular
Communications System (Phase 2+); Radio Transmission
and Reception. All GSM specifications are now the
responsibility of 3GPP. The standards are available at
http://www.3GPP.org/specs/specs.htm
Figure 7. ESD Sensitivity Areas
Various failure criteria can be utilized when performing ESD
testing. Many vendors employ relaxed ESD failure standards,
which fail devices only after “the pin fails the electrical
specification limits” or “the pin becomes completely nonfunctional”. Skyworks employs most stringent criteria, fails
devices as soon as the pin begins to show any degradation on a
curve tracer.
The four main functions described in this section are Standby
Mode Control, Band Select, Voltage Clamp, and Current Buffer.
The functional block diagram is shown in Figure 8.
To avoid ESD damage, latent or visible, it is very important the
Class-1 ESD handling precautions listed below are observed in
the product assembly and test areas.
• Personnel Grounding
- Wrist Straps
- Conductive Smocks, Gloves and Finger Cots
- Antistatic ID Badges
• Facility
- Relative Humidity Control and Air Ionizers
- Dissipative Floors (less than 109 Ω to GND)
• Protective Workstation
- Dissipative Table Tops
- Protective Test Equipment (Properly Grounded)
- Grounded Tip Soldering Irons
- Conductive Solder Suckers
- Static Sensors
• Protective Packaging & Transportation
- Bags and Pouches (Faraday Shield)
- Protective Tote Boxes (Conductive Static Shielding)
- Protective Trays
- Grounded Carts
- Protective Work Order Holders
Figure 8. Functional Block Diagram
Standby Mode Control
The Combinational Logic cell includes enable circuitry that
monitors the APC ramping voltage from the power amplifier
controller (PAC) circuit in the GSM transmitter. Typical handset
designs directly connect the PA VCC to the battery at all times, and
for some PA manufacturers this requires a control signal to set
the device in or out of standby mode. The Skyworks PAM does
not require a Transmit Enable input because it contains a standby
detection circuit that senses the VAPC to enable or disable the PA.
This feature helps minimize battery discharge when the PA is in
standby mode. When VAPC is below the enable threshold voltage,
the PA goes into a standby mode, which reduces battery current
(ICC) to 6 µA, typical, under nominal conditions.
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PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
DATA SHEET • CX77304-17
For voltages less than 700 mV at the APC input (pin 14), the PA
bias is held at ground. As the APC input exceeds the enable
threshold, the bias will activate. After an 8 µs delay, the amplifier
internal bias will ramp quickly to match the ramp voltage applied
to the APC input. In order for the internal bias to precisely follow
the APC ramping voltage, it is critical that a ramp pedestal is set
to the APC input at or above the enable threshold level with a
timing at least 8 µs prior to ramp-up. This will be discussed in
more detail in the following section, “Power Ramping
Considerations for 3GPP Compliance”.
Band Select
The Combinational Logic cell also includes a simple gate
arrangement that selects the desired operational band by
activating the appropriate current buffer. The voltage threshold
level at the Band Select input (pin 16) will determine the active
path of the bias output to the GaAs die.
Voltage Clamp
The Voltage Clamp circuit will limit the maximum bias voltage
output applied to the bases of the HBT devices on the GaAs die.
This provides protection against electrical overstress (EOS) of the
active devices during high voltage and/or load mismatch
conditions. Figure 9 shows the typical transfer function of the APC
input to buffer output under resistively loaded conditions. Notice
the enable function near 600 mV, and the clamp acting at 2.15 V,
corresponding to a supply voltage of 4.0 V.
Figure 10. Base Bias Clamp Voltage vs. Supply Voltage
Current Buffer
The output buffer amplifier performs a vital function in the CMOS
device by transferring the APC input voltage ramp to the base of
the GaAs power devices. This allows the APC input to be a high
impedance port, sinking only 10 µA, typical, assuring no loading
effects on the PAC circuit. The buffers are designed to source the
high GaAs base currents required, while allowing a settling time
of less than 8 µs for a 1.5 V ramp.
Power Ramping Considerations for 3GPP Compliance
The primary variables in the power control loop that the system
designer must control are:
• Software control of the DSP / DAC
• Software control of the transmitter timing signals
• Ramp profile attributes - pedestal, number of steps, duration of
steps
• Layout of circuit / parasitics
• RC time constants within the PAC circuit design
All of these variables will directly influence the ability of a GSM
transmitter power control loop to comply with 3GPP
specifications.
Figure 9. Base Bias Voltage vs. APC Input, VCC = 4.0 V
Due to output impedance effects, the bias of the GaAs devices
increases as the supply voltage increases. The Voltage Clamp is
designed to gradually decrease in level as the battery voltage
increases. The performance of the clamp circuit is enhanced by
the band gap reference that provides a supply-, process-, and
temperature-independent reference voltage. The transfer function
relative to VBAT is shown in Figure 10. For battery voltages below
3.4 V, the base bias voltage is limited by the common mode range
of the buffer amplifier. For battery voltages above 3.4 V, the
clamp limits the base bias.
Although there is a specific time mask template in which the
transmitter power is allowed to ramp up, the method is very
critical. The 3GPP system specification for switching transients
results in a requirement to limit the edge rate of output power
transitions of the mobile. Switching transients are caused by the
transition from minimum output power to the desired output
power, and vice versa. The spectrum generated by this transition
is due to the ramping waveform amplitude modulation imposed
on the carrier. Sharper transitions tend to produce more spectral
"splatter" than smooth transitions. If the transmit output power is
ramped up too slowly, the radio will violate the time mask
specification. In this condition, the radio may not successfully
initiate or maintain a phone call. If the transmit output power is
ramped up too quickly, this will cause RF "splatter" at certain
frequency offsets from the carrier as dictated by the 3GPP
specification. This splatter, known as Output RF Spectrum (ORFS)
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101943B • Skyworks Proprietary and Confidential Information • Products and Product Information are Subject to Change Without Notice. • July 29, 2004
13
DATA SHEET • CX77304-17
due to Switching Transients, will increase the system noise level,
which may knock out other users on the system. The main
difficulty with TDMA power control is allowing the transmitter to
ramp the output power up and down gradually so switching
transients are not compromised while meeting the time mask
template at all output power levels in all operational bands. The
transmitter has 28 µs to ramp up power from an off state to the
desired power level.
The GSM transmitter power control loop generally involves
feedback around the GaAs PA, which limits the bandwidth of
signals that can be applied to the PA bias input. Since the PA is
within the feedback loop, its own small-signal frequency
response must exhibit a bandwidth 5 to 10 times that of the
power control loop. As discussed in the previous section, the PA
bias is held at ground for inputs less than 700 mV. As the APC
input exceeds the enable threshold, the bias will activate. After an
8 µs delay, the amplifier internal bias will quickly ramp to match
the ramp voltage applied to the VAPC input. Since the bias must be
wide band relative to the power control loop, the ramp will exhibit
a fast edge rate. If the APC input increases beyond 1 V before the
8 µs switching delay is allowed to occur after the bias is enabled,
the PA will have significant RF output as the internal bias
approaches the applied bias. During this ramp, the internal power
control is running "open loop" and the edge rates are defined by
the frequency response of the PA bias rather than that of the
power control loop. This open loop condition will result in
switching transients that are directly correlated to the PA bias
bandwidth.
Application of an initial APC voltage, which enables the bias at
least 8 µs before the VAPC voltage is ramped, will ensure that the
internal bias of the PAM will directly follow the applied VAPC. As a
result, the power control loop will define all edge transitions
rather than the PA internal bandwidth defining the transition.
Figure 11 and Figure 12 show the relationships of the internal
bias relative to the applied APC in two cases. One case has
ramping starting from ground; the other case has ramping
starting with an initial enable pedestal of 700 mV. It is evident that
the pedestal level is critical to ensure a predictable and well
behaved power control loop.
PA MODULE FOR TRI-BAND EGSM DCS PCS / GPRS
The device specifications for enable threshold level and switching
delay are shown in Table 3.
Figure 11. PAM Internal Bias Performance—No Pedestal Applied
Figure 12. PAM Internal Bias Performance—Pedestal Applied
To enable the CMOS driver in the PAM prior to ramp-up, a PAC
output pedestal level to the APC input of the PAM (pin 14) should
be set to about 700 mV. This pedestal level should have a
duration of at least 8 ms directly prior to the start of ramp up.
Figure 13 shows typical signals and timings measured in a GSM
transmitter power control loop. This particular example is at GSM
Power Level 5, Channel 62. The oscilloscope traces are
TxVCO_enable, PAC_enable, DAC Ramp, and VAPC (pin 14).
NOTE: When the TxVCO is enabled, the pedestal becomes set at
the APC input of the PAM, then the PAC is enabled, and
finally the DAC ramp begins.
Figure 13. GSM Transmitter – Typical Ramp-up Signals
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14
July 29, 2004 • Skyworks Proprietary and Confidential Information • Products and Product Information are Subject to Change Without Notice. • 101943B
Ordering Information
Model Number
Manufacturing Part Number
Product Revision
Package
Operating Temperature
CX77304-17
CX77304-17
17
9.1 x 11.6 x 1.5 mm
–20 °C to +100 °C
Revision History
Revision
Level
Date
Description
A
September 19, 2003 Initial Release
B
July 29, 2004
Revise: Figure 3 <changed thickness dimension from “1.50 mm max.” to “1.5 ±0.1 mm” >
References
Application Note: Tape and Reel, Document Number 101568
Application Note: PCB Design and SMT Assembly/Rework, Document Number 101752
JEDEC Standard J-STD-020
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