Applications Information
Introduction
The Agilent ACPM-7891 provides
a cost effective dual or tri-band
GSM Power Amplifier (PA) solu-
tion with the additional benefit
of multi-slot GPRS operation,
giving excellent efficiency and
extended transmit time. Figure 1
illustrates how the ACPM-7891
fits into a typical dual-band or
tri-band terminal design. The
device is internally matched to
50Ω and therefore an effective
design can be implemented
quickly with a few additional
capacitors for d.c. blocking of the
output ports and bypassing of
the supply pins.
The control loop can also be
implemented quickly by using an
integrated power controller such
as the LT1758-2 from Linear
Technology. An example using
this controller is given later in
this note. The required loop per-
formance and stability can be
achieved more easily in this way,
without the need for complex
and time consuming design work
around an external error com-
parator or discrete Schottky
diode detector.
Demoboards are available, and
design engineers can evaluate
the RF performance of the
ACPM-7891 power amplifier to
implement a solution quickly by
using this application note in
conjunction with the datasheet.
Chipset
Transmit
900MHz
ACPM-7891
Switch/Diplexer
Coupler
Antenna
1800MHz
1900MHz
Baseband
DAC
Loop Control
Receive
900MHz
1800MHz
1900MHz
Figure 1. ACPM-7891 in a Typical Dual-band or Tri-band Terminal.
ACPM-7891 Performance
Figure 2 plots the actual output
power of the ACPM-7891 PA for
GSM900, DCS1800 and PCS1900
bands as a function of the con-
trol voltage, Vapc. The input
power to the PA is a GMSK
modulated RF carrier of a con-
stant power level of 2 dBm. The
PA’s maximum output power is
35 dBm in the GSM900 band,
and 33 dBm for the DCS1800/
PCS1900 band at a control volt-
age of 2.2V. The input RF carrier
and control voltage are both
pulsed, following the GSM TDMA
characteristic response with a
period of 4.615ms and a duty
cycle of 12.5~25% per the GSM
standard.
40
35
30
25
20
15
10
5
0
-5
-10
-15
-20
0.75
0.95
1.15
1.35
1.55
1.75
1.95
2.15
EGSM
DCS
PCS
Pout (dBm)
Vapc (V)
Figure 2. Output Power vs. Control Voltage for
the ACPM-7891 Power Amplifier.
12
HP [ AGILENT(HEWLETT-PACKARD) ]
