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Copyright 1997-2000 RF Micro Devices, Inc.
A high power, high efficiency, low cost power amplifier
has been developed utilizing commercial gallium ars-
enide (GaAs) heterojunction bipolar transistor (HBT)
technology. The RF2152 is suitable for 3V applications,
especially CDMA/AMPS handsets. Operating in the
IS95 bandwidth with a supply voltage of 3.4V, the
amplifier can provide 28dBm of output power (meeting
IS95 linearity requirements), with 30dB of gain and a
power added efficiency (PAE) of 38 percent.
The RF2152 is the latest addition to a family of power
amplifiers introduced by RF Micro Devices (RFMD) uti-
lizing GaAs HBT technology. This commercially proven
technology has several advantages over other technol-
ogies, such as MESFET or PHEMT. Since HBT's are
bipolar, no negative bias is required, nor is it necessary
to include a charge pump to generate this voltage,
which adds die count and cost to the product. The HBT
can be completely powered down using a control volt-
age, eliminating the need for a drain supply switch
used in MESFET designs. RFMD's HBT process also
utilized backside vias, resulting in low ground induc-
tance when used in conjunction with a slug type pack-
age. The amplifier is packaged in a 16-pin EDSSOP
package, and has been developed with low cost 0402
size components for minimizing application circuit size.
The performance summary of the RF2152 power
amplifier is shown below.
The RF2152 can also be tuned for JDMCA/TACS
(877MHz to 924 MHz) with similar performance.
The RF2152 power amplifier is packaged in an
EDSSOP-16 package with backside ground. The
dimensions for this package are shown in Figure 1.
There are currently two options available for the power
amplifier in a CDMA handset. The first is a module that
usually consists of a single package containing the
power amplifier die, and several components used for
matching and bias decoupling. The other option is to
use a packaged power amplifier MMIC, and design a
matching network externally on the phone PCB. RFMD
is currently developing products for both of these
options, with the RF2152 being a packaged MMIC
amplifier requiring external components.
The advantage of the packaged amplifier becomes
obvious when choosing the operating voltage for the
handset. In discussions with various vendors, it was
found that approximately 50 percent of handset
designs for the 3V CDMA market will use a regulated
V
CC
. In this case, there will be a single output imped-
ance that will result in optimum performance from the
power amplifier. Modules are typically designed to
operate across the entire possible region of operation,
typically 3.0V to 4.3V, for a lithium ion battery-powered
design. This requires a compromise in load line design,
since the module cannot be opened and retuned for
the various applications. Of course, for the other 50
percent of the handset designs, this load line
(designed for a wide range of V
CC
's) can also be imple-
mented on the PCB for MMIC power amplifiers.
The following discussion shows the variation in load
lines for two supply voltage conditions. The calculation
of the correct load line can be approximated by the
equation:
Frequency
824MHz to 849MHz
V
CC
3.0V to 5.0V
Output Power
31dBm AMPS
28dBm CDMA
Gain
30dB
Linearity
-44dBc @ 885kHz
-56dBc @ 1980kHz
PAE
55% AMPS
38% CDMA
.059
.051
.197
.189
.244
.228
.030
.018
8 MAX
0 MIN
.009
.008
.157
.150
.012
.008
1
.003
.001
.025
.062
.070
.102
.110
EXPOSED
HEATSINK
Figure 1. PSSOP-16 Package Outline
TA0032
TA0032
RF2152: A 3V HBT Power Amplifier for CDMA/AMPS Handsets
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Copyright 1997-2000 RF Micro Devices, Inc.
RL={(V
CC
-VSAT)^2}/(2*PSAT)
(Assuming a real load line)
Where
VCC= the supply voltage for the handset.
VSAT =the saturation voltage for the transistor (for this
example, 0.4V will be used).
PSAT =the saturated output power of the amplifier, typi-
cally 3dB above linear output power for a CDMA power
amplifier.
For a 3.0 V handset application, with 28dBm output
power at the power amplifier:
RL=2.7ohms
However, for a 4.3V handset application, with 28dBm
output power at the power amplifier:
RL=6.04ohms
In the case of a handset design using an unregulated
supply voltage, a load line must be designed that will
allow the part to meet CDMA specifications under all
these conditions. So it is obvious a compromise must
be made. In the case of a handset design using a regu-
lated V
CC
design, however, an optimum load line can
be used if the tuning is accessible to the handset
designer. Using an MMIC power amplifier makes this
optimization possible.
!"
"
#
The RF2152 utilizes the TRW/RFMD high volume low
cost commercial HBT process. This is a mature pro-
cess developed by TRW in the late 1980's. Since the
early 1990's, TRW and RFMD have worked together to
optimize this process for low cost commercial applica-
tions. A unique feature of this process is the utilization
of molecular beam epitaxy (MBE), which is an accurate
and repeatable method for growing the various transis-
tor layers. Previously viewed as an expensive research
process, MBE is now being used in low cost commer-
cial processing. This has been accomplished through
the development of multi-wafer MBE reactors at TRW.
This results in better uniformity and reduced process
variation when compared with older MOCVD-type pro-
cesses.
A major milestone in the success of this process was
reached with the recent announcement of the comple-
tion of the world's largest HBT fab located at RFMD's
headquarters in Greensboro, North Carolina. With the
implementation of cross-linked manufacturing, RFMD
and TRW will now provide customers with two geo-
graphically separated manufacturing locations for high
volume production using the same process. The only
difference is the transition to four-inch wafers at the
RFMD fab. This results in a 70 percent increase in
parts per processed wafer.
!"
"
#
As mentioned earlier, the TRW/RFMD HBT process
takes advantage of high volume MBE-based transistor
growth. In an HBT transistor, the critical geometries are
vertical, and are controlled during this MBE process.
This is very different from MESFET technologies,
where critical geometries are based on photolitho-
graphic processing steps that are dependent on mask
alignment and optical resolutions.
Additionally, the turn-on voltage (VBE) of an HBT is
controlled by the bandgap of the structure, and is not a
function of processing. With MESFET's, the turn-on
voltage (VT) is greatly affected by processing, espe-
cially surface effects such as traps. This results in large
variations in bias current, which are commonly cor-
rected using expensive post processing adjustments
such as laser trimming resistors.
the HBT process also allows wafers to be completed
and stockpiled, thus eliminating several steps from the
critical path of production development.
Finally, the minimum geometries in the HBT process
are 2
m, typically two to four times the gate geome-
tries found in MESFET's. This also increases the man-
ufacturability of this process.
!"
"
#
There are many advantages to using HBT technology
in power amplifiers, rather than the older MESFET and
HEMT-based approaches. One of the biggest is sim-
plicity for the customer's designs. HBT's, unlike MES-
FET's, do not require any negative voltages for
operation, so a charge pump is not required either in
the IC package (where it will use current) or in the
handset (where it will add cost).
Another advantage is power control. All power amplifi-
ers require some means of power-down control to
reduce battery current consumption when not in use. In
MESFET-based designs, the conventional means for
power-down control is to use an external "drain side
switch" to disconnect the battery voltage, and shutting
down the charge pump supplying gate bias. This "brute
force" approach is required because the alternative
would be to design a charge pump to provide addi-
tional negative voltage to fully deplete the MESFET,
which would consume too much current.
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Copyright 1997-2000 RF Micro Devices, Inc.
There are two negative results with using a drain side
switch. First, the cost of an added component. Second,
the voltage drop across the switch, which must be con-
sidered when comparing PAE results with HBT power
amplifiers.
For example, assuming two amplifiers (one MESFET
and one HBT), both operating at 3.0V, 28dBm out, 40
percent PAE, and the drain side switch has a voltage
drop of 0.15V. This would require that 3.15V be sup-
plied to the MESFET amplifier to have 3.0V at the
drain. This would result in a drop of two PAE percent-
age points.
Looking at this another way, the affect of a drain side
switch on talk time is even more apparent. Assuming
the battery was allowed to run down to 3.0V before
shutting the phone off, and both PA running at 40 per-
cent efficiency, the following currents are derived:
PA without drain switch (i.e., HBT PA)
28dBm out =0.63 W
40 percent PAE
I
CC
= 0.63W/(3.0 V*0.4)
I
CC
= 525 mA
However, in a PAE with a drain switch, the voltage at
the drain will be 2.85V. Assuming the load line was
reoptimized to provide 40 percent PAE, the current
required will be:
I
DD
= 0.63W/(2.85V*0.4)
I
DD
= 552 mA
The result is a five percent increase in current con-
sumption in a FET-based amplifier at low battery volt-
age.
"
#
$
A functional block diagram of the RF2152 is shown in
Figure 2.
As shown above, the RF2152 is a two-stage power
amplifier with internal bias circuits. Interstage tuning is
accomplished partially off-chip to account for board
ground inductance from various manufacturing tech-
nologies. Power down and low power modes are con-
trollable via external pins.
The first stage ground is brought out through a sepa-
rate pin for isolation from the output stage. The output
stage is grounded through the package slug.
The following is a description of the various I/O's.
Pin
Function
1
Supplies VCC to the bias circuits
2
Interstage tuning control
3
No Connect
4
Supplies VCC to the first stage
5
Ground for the first stage
6
RF input
7
Bias fine control
8
Power down control
9
No Connect
10
No Connect
11
No Connect
12
RF Out
13
RF Out
14
Harmonic Trap
15
No Connect
16
VMODE (output bias adjustment
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VCC
LTUNE
NC
VCC1
GND1
RF IN
VPD
VPD
MODE
NC
RF OUT
RF OUT
RF OUT
NC
NC
NC
BIAS
CIRCUITS
PACKAGE BASE
GND
Figure 2. Block Diagram of RF2152
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Copyright 1997-2000 RF Micro Devices, Inc.
The application schematics for the most common
applications (IS95 CDMA) are shown in Figure 3.
It should be noted that many of the capacitors shown
for bias decoupling have been found necessary to
reduce test equipment noise on a test bench, but
unnecessary in an actual handset with a battery.
The evaluation board layout, containing the power
amplifier and matching components, may be found in
the RF2152 data sheet.
%
& #
To demonstrate the possible utilization of the RF2152,
typical parts were tuned for use across a wide supply
voltage range of 3.0 V to 5.0 V. This would demonstrate
the typical requirements of a handset using very low
cost NiCad batteries with a typical charger voltage of
5.0 V. Figures 4 through 18 show the amplifier perfor-
mance overall bias and temperature conditions, with-
out retuning the part.
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
BIAS
CIRCUITS
R3
VPD
100
pF
100
pF
RF
IN
1.2
nH
47
nH
100
pF
V
CC
1
nH
2
pF
9
pF
7
pF
100
pF
RF
OUT
MOD
E
100
pF
100
pF
100
pF
L6 may be implemented as a transmission
line to reduce DC losses.
R3 is used for bias adjustment. 0
for 2.8V
regulated supply.
All unused pins should be grounded to PC
board if possible.
L6
20 nH
2.7
nH
PACKAGE BASE
Figure 3. RF2152 Applications Circuit
ACPR (@885 kHz offset) vs. Frequency
Vcc=3.5 V, Vreg=2.8 V, CDMA Pout=28 dBm
-50
-49
-48
-47
-46
-45
-44
-43
-42
-41
-40
820
825
830
835
840
845
850
855
Frequency (MHz)
ACPR (dBc)
Lower -30 C
Upper -30 C
Lower + 25 C
Upper +25 C
Lower +85 C
Upper +85 C
Figure 4. CDMA Mode: Adjacent Channel Linearity
ACPR (@1980 kHz offset) vs. Frequency:
Vcc=3.5 V, Vreg=2.8 V, CDMA Pout=28 dBm
-68
-66
-64
-62
-60
-58
-56
-54
-52
820
825
830
835
840
845
850
855
Frequency (MHz)
ACPR (dBc)
Lower -30 C
Upper -30 C
Lower +25 C
Upper +25 C
Lower +85 C
Upper +85 C
Figure 5. Alternate Channel Linearity
Gain vs. Frequency
Vcc=3.5 V, Vreg=2.8 V, CDMA Pout=28 dBm
30
30.5
31
31.5
32
32.5
33
33.5
34
820
825
830
835
840
845
850
855
Frequency (MHz)
Gain (dB)
-30 C
+25 C
+85 C
Figure 6. Gain versus Frequency
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PAE vs. Frequency
Vcc=3.5 V, Vpd=2.8 V, CDMA Pout=28 dBm
30
31
32
33
34
35
36
37
38
39
40
820
825
830
835
840
845
850
855
Frequency (MHz)
PAE (%)
-30 C
+25 C
+85 C
Figure 7. PAE versus Frequency
ACPR (@885 kHz offset) vs. Frequency
Vcc=3.0 V, Vreg=2.8 V, CDMA Pout=27 dBm
-48
-47
-46
-45
-44
-43
-42
-41
-40
820
825
830
835
840
845
850
855
Frequency (MHz)
ACPR (dBc)
Lower -30 C
Upper -30 C
Lower +25 C
Upper +25 C
Lower +85 C
Upper +85 C
Figure 8. Adjacent Channel Linearity (3.0V)
ACPR (@1980 kHz offset) vs. Frequency
Vcc=3.0 V, Vreg=2.8 V, CDMA Pout=27 dBm
-66
-64
-62
-60
-58
-56
-54
820
825
830
835
840
845
850
855
Frequency (MHz)
ACPR (dBc)
Lower -30 C
Upper -30 C
Lower +25 C
Upper +25 C
Lower +85 C
Upper +85 C
Figure 9. Alternate Channel Linearity (3.0 V)
Gain vs. Frequency
Vcc=3.0 V, Vreg=2.8 V, CDMA Pout=27 dBm
30
30.5
31
31.5
32
32.5
33
33.5
34
820
825
830
835
840
845
850
855
Frequency (MHz)
Gain (dB)
-30 C
+25 C
+85 C
Figure 10. Gain versus Frequency (3.0V)
PAE vs. Frequency
Vcc=3.0 V, Vreg=2.8 V, CDMA Pout=27 dBm
32
33
34
35
36
37
38
39
40
41
42
820
825
830
835
840
845
850
855
Frequency (MHz)
PAE (%)
-30 C
+25 C
+85 C
Figure 11. PAE versus Frequency (3.0V)
ACPR (@885 kHz offset) vs. Frequency
Vcc=5.0 V, Vreg=2.8 V, CDMA Pout=28 dBm
-52
-51
-50
-49
-48
-47
-46
-45
-44
820
825
830
835
840
845
850
855
Frequency (MHz)
ACPR (dBc)
Lower -30 C
Upper -30 C
Lower +25 C
Upper +25 C
Lower +85 C
Upper +85 C
Figure 12. Adjacent Channel Linearity (5.0 V)
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ACPR (@1980 kHz offset) vs. Frequency
Vcc=5.0 V, Vreg=2.8 V, CDMA Pout=28 dBm
-60
-59
-58
-57
-56
-55
-54
-53
-52
820
825
830
835
840
845
850
855
Frequency (MHz)
ACPR (dBc)
Lower -30 C
Upper -30 C
Lower +25 C
Upper +25 C
Lower +85 C
Upper +85 C
Figure 13. Alternate Channel Linearity (5.0V)
PAE vs. Frequency
Vcc=5.0 V, Vreg=2.8 V, CDMA Pout=27 dBm
20
21
22
23
24
25
26
27
28
29
30
820
825
830
835
840
845
850
855
Frequency (MHz)
PAE (%)
-30 C
+25 C
+85 C
Figure 14. PAE versus Frequency (5.0V)
Gain vs. Frequency
Vcc=5.0 V, Vreg=2.8 V, CDMA Pout=28 dBm
29
29.5
30
30.5
31
31.5
32
32.5
33
820
825
830
835
840
845
850
855
Frequency (MHz)
Gain (dB)
-30 C
+25 C
+85 C
Figure 15. Gain versus Frequency (5.0V)
AMPS Mode
Vcc=3.0 V, Vreg=2.8 V, Pout=30.5 dBm
20
25
30
35
40
45
50
55
60
65
820
825
830
835
840
845
850
855
Frequency (MHz)
Gain (db)/PAE (%)
T=-30 PAE
T=25 PAE
T=85 PAE
T=-30 Gain
T=25 Gain
T=85 Gain
Figure 16. AMPS Mode Performance (3.0V)
AMPS Mode
Vcc=3.5 V, Vreg=2.8 V, Pout=31.5 dBm
20
25
30
35
40
45
50
55
820
825
830
835
840
845
850
855
Frequency (MHz)
Gain (db)/PAE (%)
T=25 PAE
T=85 PAE
T=-30 PAE
T=-30 Gain
T=25 Gain
T=85 Gain
Figure 17. AMPS Mode Performance (3.5V)
AMPS Mode
Vcc=5.0 V, Vreg=2.8 V, Pout=31.5 dBm
26
28
30
32
34
36
38
40
820
825
830
835
840
845
850
855
Frequency (MHz)
Gain (db)/PAE (%)
T=85 PAE
T=25 PAE
T=-30 PAE
T=-30 Gain
T=25 Gain
T=85 Gain
Figure 18. AMPS Mode Performance (5.0V)
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' & #
The data below shows the performance of an RF2152
power amplifier tuned for optimal performance at 3.5 V.
While CDMA power amplifier performance is typically
specified at 27dBm to 28dBm output power, the actual
average operating output power of a CDMA handset is
typically 10 dBm to 15dBm. With this in mind, the
RF2152 utilizes two external bias control pins to lower
the quiescent current approximately 50 percent in low
power (less than 15 dBm) mode.
Pin 16 (VMODE) directly controls the output bias. Pull-
ing this line TTL low will reduce the bias in the output
stage by about 50 percent. Pin 7 is a fine adjustment
for both stages. Depending on the output power
required in the handset design, this line can be used
for further bias reduction in low power mode.
The RF2152 HBT is an integrated power amplifier on
the market for IS95 CDMA and dual CDMA/AMPS
applications. The amplifier offers the handset designer
the opportunity to optimize an amplifier for their partic-
ular application with excellent performance. The ampli-
fier is optimized for CDMA performance, with excellent
efficiency and low power mode aimed at improving
talktime in 3V handsets.
FREQ
PIN
ICC
ACP1
ACP2
EFF
824
-3.5
469
44/44
58/59
38%
836
-4.4
460
44/44
58/59
39%
849
-4.6
444
44/44
58/59
40%
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