SKY77328 Datasheet, PDF (16/19 Pages) Skyworks Solutions Inc. – iPAC PAM for Quad-Band GSM/GPRS

DATA SHEET
SKY77328 iPAC™ PAM FOR QUAD-BAND GSM / GPRS
Technical Information
Closed loop control of the amplifier is enabled when ENABLE is
driven to logic high. The PA collector current will then be directly
proportional to the VAPC input voltage over the range of 200 mV to
2.1 V.
To meet the GSM power versus time mask and switching transient
requirements the PAM must be provided with a DAC ramp profile
on the VAPC input as well as proper timing on digital controls for the
PAC circuitry.
Note:
Please refer to 3GPP TS 51.010-1: Mobile Station (MS)
conformance specification. All GSM specifications
are now the responsibility of 3GPP. The standards
are available at http://www.3GPP.org.
The SKY77328 has been designed to comply with interface
requirements and DAC resolution of leading base band devices.
The ramp profile typically consists of a pedestal voltage, 10–16
discrete voltage steps on the rising edge of the burst, a constant
region, 10–16 steps on the falling edge, and a final voltage.
Typically, the user defines the start, stop, and 10–16 percentage
values for each rising and falling edge, which are then applied as
discrete voltages at the VAPC input. For the SKY77328, generally
the same profile, scaled in amplitude, is used for all frequencies
and power control levels. The ultimate purpose is to keep the RF
output power ramp within the time mask and to maintain
acceptable spectral limits at specified offset frequencies. The VAPC
input has an internal reconstruction filter such that external
resistors or capacitors are unnecessary on the phone board or the
test fixture.
Figure 7 represents the dynamic characteristics of the RF output
burst power that results from the ramp profile delivered by the
DAC to the VAPC input. The transmit power must not exceed the
given limits at the time specified relative to the start and end of
the data burst. Additional requirements are placed on spectral
components generated by switching transients. Ramping at high
rates will result in components that violate these spectral limits. A
ramp control signal must be applied to the VAPC pin, which results
in the desired power ramp response. The log relationship of VAPC
to POUT, along with the finite bandwidth and potential slew rate
limitations of the feedback loop, results in a complex mapping of
the ramp profile to the actual output power. Careful attention is
required in generating the input waveform which results in the
desired output response.
Figure 8 shows an example of the Skyworks PAM test setup for
evaluation of RF performance with various ramp profiles. The
user’s test setup may also include a TX/RX switch and a diplexer
in the output signal path. Alternatively, the SKY77328 PAM may
be installed in a phone board.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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March 17, 2009 • Skyworks Proprietary and Confidential Information. • Products and product information are subject to change without notice. • 103237A