Amplifier Module. SKY77344-21 Datasheet

SKY77344-21 Module. Datasheet pdf. Equivalent

SKY77344-21 Datasheet
Recommendation SKY77344-21 Datasheet
Part SKY77344-21
Description Power Amplifier Module
Feature SKY77344-21; APPLICATION NOTE SKY77344-21 Power Amplifier Module — Evaluation Information Applicability: SKY77344.
Manufacture Skyworks Solutions
Datasheet
Download SKY77344-21 Datasheet




Skyworks Solutions SKY77344-21
APPLICATION NOTE
SKY77344-21 Power Amplifier Module — Evaluation
Information
Applicability: SKY77344 Version -21
Introduction
This Application Note describes the functionality, board layout and applications instructions of the SKY77344-21 Power Amplifier Module.
The SKY77344-21 Power Amplifier Module (PAM) is designed for quad-band cellular handsets comprising GSM850/900, DCS1800/
PCS1900, and supports Class 12 General Packet Radio Service (GPRS) multi-slot operation, and Enhanced Data GSM Environment (EDGE)
(8PSK) linear modulation. A single analog control voltage is used at the VRAMP port for both GMSK and EDGE modes. The active logic level
at the MODE terminal determines the function of the VRAMP signal.
The EDGE mode is supported with a linear open loop configuration where amplifier gain is held constant with VRAMP and output power is
determined by input power. GMSK mode is supported by operating the SKY77344-21 as a variable gain amplifier where VRAMP controls
gain and resultant output power.
The SKY77344-21 PAM consists of an Indium Gallium Phosphide (InGaP) PA block, a BiCMOS multi-function controller (MFC) block, and
impedance-matching circuitry. The new BiCMOS collector voltage amplitude controller (COVAC) provides envelope amplitude control and
bias optimization for each mode of operation, thus reducing sensitivity to input drive, temperature, power supply, and process variations.
Embedded within a single Gallium Arsenide (GaAs) die using InGaP technology, one Heterojunction Bipolar Transistor (HBT) PA lineup
supports the GSM850/900 bands and another supports the DCS1800 and PCS1900 bands.
The module also contains band select switching circuitry to select GSM (logic 0) and DCS/PCS (logic 1) as determined from the Band
Select (BS) signal. As determined by the MODE control, VRAMP controls the level of output power for GMSK modulation or optimizes the
performance for EDGE modulation. The Enable input signal allows initial turn-on of the PAC circuitry to minimize battery drain.
Figure 1. SKY77344-21 Functional Block Diagram
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201236A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 16, 2010
1



Skyworks Solutions SKY77344-21
APPLICATION NOTE
SKY77344 POWER AMPLIFIER MODULE – EVALUATION INFORMATION
OPERATIONAL CONSIDERATIONS
The SKY77344-21 is intended for multi-modulation GSM/GPRS/EDGE handset applications. The next two sections will describe how the
module should be configured for use with GSM/GPRS and the EDGE waveforms.
GSM/GPRS OPERATION
For GMSK operation, set EN input high and MODE low (< 0.5 V). Select the desired TX band by setting the BS low (CEL/EGSM) or high
(DCS/PCS). VRAMP is a pulsed ramp input that controls the module output power in a manner similar to a traditional “VAPC” or “VPC”
input control signal. The pulsed ramp profile is optimized with the baseband DAC control software to be compliant with PVT and ORFS due
to switching system specifications.
VRAMP Filter
It is advisable to use a first order RC network on VRAMP line to filter noise introduced by the baseband DAC. The filter should be designed
so as to not slow down the power mask timing requirements.
Recommended RC network values are: R = 110 Ω, C = 10 nF, (FPOLE = 145 kHz).
Depending upon the baseband DAC operating characteristics, the RC network can be redesigned or eliminated. The values selected for
the RC network are critical for correct saturation detection / correction operation. A limit of R < 1 kΩ is recommended.
Power Control Scheme
An integrated power control scheme is used to control the PA output power for GMSK operation. The COVAC configuration combined with
a coupler / log detector provides a closed loop feedback mechanism. The COVAC scheme is based on limiting power at the collector by
limiting collector voltage while the feedback path monitors output power. During saturated GMSK operation, the RF input drive is held
constant while saturation characteristics of the amplifier are used to control output power. Reduction of the collector voltage of the
amplifier driver stages forces saturation, effectively limiting the large signal gain and reducing the drive level to the final stage amplifier.
Coincident reduction of the quiescent current in the amplifier provides reduction of the small signal gain along with reduced current drain.
Significant reduction of the final stage bias point below the base-emitter voltage is required to meet aggressive low power performance as
well.
Table 2 is a simplified schematic of PA control scheme which senses the detected output power, compares it to the external VRAMP
signal and sets the required bias voltage at the PA collector.
Figure 2. SKY77344-21 Power Control Scheme – GMSK Mode
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
2 February 16, 2010 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 201236A



Skyworks Solutions SKY77344-21
SKY77344 POWER AMPLIFIER MODULE – EVALUATION INFORMATION
APPLICATION NOTE
Saturation Detection/Correction Operation Description and External VRAMP Filter Guideline
When the SKY77344-21 PAM saturates under conditions of low battery and/or VSWR, a decrease in the internal power control loop gain-
bandwidth occurs, producing high level switching transients on the falling edge of the burst. To prevent this condition, the SKY77344-21
includes an autonomous saturation detection / correction function. When saturation is detected, output power is reduced by approximately
0.5 dB which is sufficient to increase the loop gain-bandwidth to a level that restores switching transients to specification compliance
(with additional production margin).
Under some environmental conditions, the PA may enter soft saturation, which is the transition region between no saturation and hard
saturation. To ensure compliant switching transients in this region, the PA is “tested” for soft saturation by pushing the PA into hard
saturation. This is achieved by reducing the output power approximately 0.5 dB about 100 μs after the start of every burst. This “correct
every burst” feature occurs for all VRAMP levels greater than 1.0 V. Saturation is detected during the first 100 μs or “high” part of the
carrier power envelope followed by the required power reduction. Whether the PA is saturated or non-saturated, a ~0.5 dB power
correction will be observed for all VRAMP levels greater than 1.0 V. Nominally, this power correction will occur ~100 μs after the start of the
burst.
However, as VRAMP exceeds the voltage required for nominal rated output power (~1.85 V), the correction duty cycle will increase from
100 μs / 577 μs (17%) to 100%. As the applied VRAMP is increased beyond that required for nominal rated power, the internal VRAMP, which
references the internal PA control loop, must be further decreased to pull the control loop out of saturation. Since the internal pullback
time constant is fixed, this action requires additional time and results in increasing the correction duty cycle. For VRAMP greater than
~2.2 V, which is beyond the normal operating region of the device, the duty cycle is ~100% and the saturation detection/correction
circuitry is no longer active.
Under conditions of low battery and/or VSWR PA load, where the saturated PA output power (PSAT) has decreased, the correction duty
cycle will also increase beyond the nominal 17%. The internal VRAMP must be decreased below the lower VRAMP @PSAT value to pull the
control loop out of saturation. Since the internal pullback time constant is fixed, this action requires additional time or longer correction
duty cycle. To ensure part-to-part constancy, the correction factor (~0.5 dB for Low Band, ~0.4 dB for High Band) is screened at
production test.
Figure 3 illustrates a block diagram of the saturation detection/correction technique used in the SKY77344-21. Depicted are the power
amplifier, detector, collector voltage power control loop, and the saturation detection/correction functions, VRAMP comparator, timer,
correction offset ramp generator, IOFFSET current source, and saturation detector.
Figure 3. SKY77344-21 Block Diagram of Saturation Detection / Correction Technique
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
201236A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 16, 2010
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