iPAC™ FEM FOR QUAD-BAND GSM / GPRS
DATA SHEET • SKY77500
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.
Open Loop Control Mode
With PAC ENABLE at logic low, the voltage applied to VAPC is
buffered and applied directly to the bases of the RF devices. This
mode of operation provides backward compatibility with the
existing amplifier designs and allows for various test scenarios.
As with previous designs, an active clamp acts as a protection
mechanism limiting the maximum voltage that can be applied to
the base of the RF devices. This clamp voltage decreases with
increasing supply voltage.
The enable threshold on the VAPC input for open loop operation
exhibits a wide tolerance, which may vary from 200 mV to
800 mV. When enabled in Open Loop mode, the internal PAC
circuitry (V-I converter and integrator) is placed in standby.
Figure 9 shows an example of the Skyworks FEM test setup for
evaluation of RF performance with various ramp profiles.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
103146A • Skyworks Proprietary information. • Products and product information are subject to change without notice. • May 16, 2005
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