參數(shù)資料
型號(hào)： CX77304-15
廠商： SKYWORKS SOLUTIONS INC
元件分類： 放大器
英文描述： 2MM SOCKET STRIPS
中文描述： 824 MHz - 849 MHz RF/MICROWAVE NARROW BAND MEDIUM POWER AMPLIFIER
封裝： 9.10 X 11.60 MM, 1.50 MM HEIGHT, LEAD FREE, PLASTIC, LEADLESS, SO-16
文件頁(yè)數(shù)： 8/20頁(yè)
文件大?。?/td> 620K
代理商： CX77304-15
Technical Information
CX77304-15
PA Module for Dual-Band GSM850 PCS1900 / GPRS Applications
16
Skyworks Solutions, Inc.
101749A
Proprietary Information
September 19, 2003
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) 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
s 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 700mV. As the APC input exceeds the enable threshold, the bias will activate. After
an 8
s 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 1V before the 8
s 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
s 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. Figures 10 and 11 show the relationship 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.
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
s directly prior to the start of ramp up.
Figure 12 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.
The device specifications for enable threshold level and switching delay are shown in Table 3.
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參數(shù)描述
CX77304-16 制造商:SKYWORKS 制造商全稱:SKYWORKS 功能描述:CX77304-16 PA Module for Tri-Band EGSM DCS PCS / GPRS
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CX77314 制造商:未知廠家 制造商全稱:未知廠家 功能描述:CX77314 Product Summary|PA Modules for GSM/GPRS Handsets
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