Transmitter architectures and system design

kinpoagilent

【文件名】:071012@52RD_HFE0605_McCambridgeandWhitaker.pdf
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bjohn

Combination Closed Loop
and VCC Power Control for
a GSM/GPRS PA
By Paul McCambridge, Xindium Technologies, and
Brian Whitaker, Maxim Integrated Products
Power control is an
important performance
specification
for GSM/GPRS wireless
handsets. This article
shows how the MAX4002
low-cost, low-power logarithmic
amplifier and
power detector, and the XIN9133 quad-band
GSM/GPRS power amplifier (PA) are combined
in a closed loop power control system
with the added advantage of PA protection
through supply voltage power control. This
results in significant advantages over today’s
predominant GSM power control solutions on
the market.
Power Control Requirements
Important requirements for power amplifiers
in a GSM cell phone are:
• Adjustable and precision-set output power.
• The PA is not allowed to transmit outside its
frequency band (a precise power ramp control
is needed to eliminate out-of-band noise).
• The PA is only allowed to transmit in its
own timeslot, not in others (requiring tight
ramp control).
When a PA is used without control, it is difficult
to meet the GSM specifications, because
the PA by itself is not accurate enough.
Reasons for inaccuracy include:
• The PA is a non-linear device.
• The PA gain and output power varies with
frequency, battery voltage and temperature.
• Gain control slopes of PAs vary across device
populations.
There

bjohn

Combination Closed Loop
and VCC Power Control for
a GSM/GPRS PA
By Paul McCambridge, Xindium Technologies, and
Brian Whitaker, Maxim Integrated Products
Power control is an
important performance
specification
for GSM/GPRS wireless
handsets. This article
shows how the MAX4002
low-cost, low-power logarithmic
amplifier and
power detector, and the XIN9133 quad-band
GSM/GPRS power amplifier (PA) are combined
in a closed loop power control system
with the added advantage of PA protection
through supply voltage power control. This
results in significant advantages over today’s
predominant GSM power control solutions on
the market.
Power Control Requirements
Important requirements for power amplifiers
in a GSM cell phone are:
• Adjustable and precision-set output power.
• The PA is not allowed to transmit outside its
frequency band (a precise power ramp control
is needed to eliminate out-of-band noise).
• The PA is only allowed to transmit in its
own timeslot, not in others (requiring tight
ramp control).
When a PA is used without control, it is difficult
to meet the GSM specifications, because
the PA by itself is not accurate enough.
Reasons for inaccuracy include:
• The PA is a non-linear device.
• The PA gain and output power varies with
frequency, battery voltage and temperature.
• Gain control slopes of PAs vary across device
populations.
There.........[em07]