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Mobile Communications
LTE PAs Offer Fast,
Powerful Wireless
Data Options�
C
onsumers are demanding more from
their mobile devices, including increased bandwidth. They have become
accustomed to the near universal data connectivity of smartphones and tablets including applications that continually demand higher and
higher data rates. Given the variety of LTE
frequency bands, and the range of preferred
power levels, RFMD has developed a family
of LTE-compatible power amplifiers for data
connectivity applications. They are summarized in Table 1.
TABLE I
RFMDs family of power amplifiers for LTE dAta connectivity
Part
Number
Frequency
Range
(GHz)
Integration
Linear
Power
(dBm)
Supply
Voltage
(V)
Current
(mA)
RF5602
2.3 to 2.7
Unmatched PA
21 to 23
3.3 to 5
350 to 450
RF5603
3.3 to 3.8
Unmatched PA
23
3.3
425
RF5607
1.9 to 2.7
Unmatched PA
22
5
350
RF5612
2.5 to 2.7
Matched PA
22
3.3
470
RF5623
3.3 to 3.8
Unmatched PA
24
5
600
RF5652
2.3 to 2.7
Unmatched PA
28
5
1200
RFFM7600
2.3 to 2.7
Matched PA+SPDT
24
5
650
32
As can be seen, a wide range of LTE bands
can be covered by these PAs. The RF5607,
for example, has a large frequency coverage
capability of 1.9 to 2.7 GHz. This allows the
customer to tune to a desired frequency band
within this range. The RF5602 is similar and
offers higher output power with less frequency
coverage. It can also be efficiently operated
at lower power with a reduced Vcc. The linear
power listed for each of these amplifiers is for
a nominal linearity requirement, and varies depending on the specific modulation used. The
RF5612 is intended for uplink applications, the
others are primarily intended for the downlink.
Many of the amplifiers in Table 1 can also be
used in WiMAX applications, typically at higher output powers. RFMD continues to add to
its LTE power amplifier family, with higher
power levels in particular, soon to be available.
RF5607
The RF5607 is a versatile member of
RFMD’s LTE power amplifier family. It is
RF Micro Devices
Greensboro, NC
MOBILE COMMUNICATIONS n NOVEMBER 2011
Mobile Communications
VCC1
N/C
VCC2
VCC2
16
15
14
13
BIAS VCC 1
12 RF OUT
1st
STAGE
3rd
STAGE
2nd
STAGE
INTERSTAGE
MATCH
INTERSTAGE
MATCH
RF IN 2
10 RF OUT
VREG2
6
7
8
VREG3
N/C
PDETECT
L6
3.9 nH
1
12
2
11
3
10
4
9
5
6
7
C9
5.6 pF
8
Block diagram of the RF5607.
R3
56 C7
330 pF
C2
1000 pF
PDOWN
s Fig. 3
VREG2
PDET
Schematic of the RF5607 in a 2.1 to 2.2 GHz application.
G (dB)
ACP (dBc)
ure 4. As shown,
ACLR
remains
–25
well below the -44
–30
–35
dBc requirement
–40
up to 22 dBm out–45
put power. At that
–50
point, nonlineari–55
ties resulting from
–60
–65
the large peak to
0
5
10
15
20
25
30
average power raPO (dBm)
tio (PAPR) of the
modulated
sig- s Fig. 4 Typical linearity performance of the
nal begin to de- RF5607 with a 10 MHz modulated LTE signal
grade ACLR. The at frequencies between 2.11 and 2.17 GHz.
RF5607 actually
40
0.50
provides -45 dBc
35
0.45
ACLR.
30
0.40
Gain and cur25
0.35
20
0.30
rent consumption
15
0.25
are also impor10
0.20
tant power ampli5
0.15
fier characteristics.
0
0.10
5
10
15
20
25
They are shown
PO (dBm)
versus
output
power in Figure
Fig. 5 Typical gain and current consump5. Note how gain s
tion performance of the RF5607 with a 10
is only lightly com- MHz modulated LTE signal at frequencies
pressed even at between 2.11 and 2.17 GHz.
the full LTE rated
power of 22 dBm. This highlights the very linear operation
that LTE downlinks demand. The current consumption is
below 330 mA, even at 22 dBm. Current increases gradually from about 230 mA at quiescence. Since the output stage
operates in deep Class AB, the low impedance active bias
ICC (A)
designed
using
RFMD’s
InGaP
HBT process. The
block
diagram,
Figure 1, shows
that this is a threestage power amplifier with integrated
power detection
and active bias
s Fig. 2 The RF5607 LTE downlink PA ap- control. All stages
plication board for 2.1 to 2.2 GHz operation. use a 3 × 20 µm
dual emitter HBT
unit cell. Two cells are used in the first stage. The second
and third stages are scaled up to 8 and 32 cells, respectively.
The PA operates in Class AB mode. The second harmonic termination at the output is implemented with an
on-chip capacitor and an in-package down bond. The first
and second stages are each biased with a two-diode emitter
follower. RFMD’s proprietary active bias circuit supplies
bias to the final stage while providing low impedance for
linear operation over the operating range.
A unique feature of the RF5607 is that the input and
output matching networks are off chip. Interstage matching is broadband to cover the entire 1.9 to 2.7 GHz frequency range. Actual applications are in much narrower
bands within this range. Ultimate performance is critically
dependent on output match and to a lesser extent on input
match. Therefore, optimized matching for specific LTE
downlink bands has been developed for implementation
off-chip. Figure 2 shows an application board for 2.1 to
2.2 GHz operation. The application boards for other bands
are identical, only the values of the matching components
change.
The schematic, with matching components optimized for
a 2.1 to 2.2 GHz LTE downlink is shown in Figure 3. The
RF5607 uses a 3 × 3 mm QFN package. ESD protection is
included on all pins to both Human Body Model (HBM)
and Charged Device Model (CDM) requirements. The exact band of operation is tunable with external components.
The key performance attributes for an LTE power amplifier are power, ACLR and current consumption. Typical power and linearity for the RF5607 are shown in Fig
16 15 14 13
C8
3.3 pF
5
L5
3.9 nH
C16
1 uF
C19
3.3 pF
9 N/C
VREG1 4
J1
RF IN
R1
15 C3
1 pF
L3
12 nH
J2
RF OUT
DETECTOR
BIAS
34
C1
1000 pF
C11
1 uF
R4
100 C13
330 pF
11 RF OUT
PDOWN 3
s Fig. 1
VCC
(Continued on page 38)
MOBILE COMMUNICATIONS n NOVEMBER 2011
Mobile Communications
Intermod Squad:
Low PIM Connectors
D
ubbed the Intermod Squad, Santron has developed a new series
of low PIM cable assemblies that
feature intermodulation performance as
low as -181 dBc with an eSeries 7/16 connector terminated on TFlex-402 cable.
Typical performance across the lineup of
assemblies terminated with eSMA and
eSeries Type N’s is -162 dBc. The eSMA
cable assemblies perform from DC to 20
GHz and the eSeries Type N cable assemblies perform from DC to 18 GHz.
These assemblies are phase and attenuation stable, provide excellent shielding,
support UL/NEC Plenum class CMP,
are corrosion resistant, and are low in
weight and highly flexible.
The key component in San-tron low
PIM cable assemblies are the latest series of connectors. eSeries connectors,
which include SMA (trademarked as
eSMA), Type N, TNC and 7/16 styles,
offer evolved cable/connector transitions. The repeatability of these transitions from the cable into the connector
is key to the consistent high performance
of these cable assemblies. The center
contact is a solder-free connection so
the transition is controlled to machined
tolerances, which are much tighter than
the variations seen by cable assembly
personnel and solder joints. Another advantage of the elimination of this center
conductor solder joint is it precludes the
changes that occur in dielectric densities
that would affect changes in the dielectric constant. Also, the connector bodies contain an internal stop to locate the
cable position into the connector.
Reliability is improved with these
connectors with an extended ferrule
that is crimped onto the body that provides longitudinal protection out past
this wick line, which is a traditional fail-
ure point. For added protection, dual
wall heat shrink is positioned within the
saddle of this crimp ferrule and further
extends the strain relief from this wick
line offering high reliability in applications that involve repeated flexure.
The Albaloy plating provides a robust surface that easily accepts the
braid solder joint and supports corrosion resistance per salt fog testing. The
eSMA center contacts are BeCu; they
are plated gold over a copper strike
providing excellent RF performance,
corrosion resistance and control over
porosity. The eSeries N and 7/16 center
contacts are plated silver over a copper
strike, which contains cost versus gold,
and also provides good RF performance
and corrosion resistance.
San-tron Inc.,
Ipswich, MA (978) 356-1585,
www.santron.com.
ACP (dBc)
(Continued from page 34)
–25
–30
–35
–40
–45
–50
–55
–60
–65
0
5
10
15
20
PO (dBm)
25
30
s Fig. 6
Typical linearity performance of
the RF5607 with a 10 MHz modulated LTE
signal (blue) and a 5 MHz W-CDMA modulated signal (black) at frequencies between
2.11 and 2.17 GHz.
network allows current to increase so
that linearity is maintained as drive
level grows.
Figure 6 shows the power and
linearity performance of the RF5607
with both a LTE downlink signal and
a W-CDMA signal. LTE has a wider
modulated bandwidth and a higher
38
data rate than W-CDMA. This increases the linearity demands on the
system and on the PA. As Figure 6
shows, this can be directly seen in
power amplifier performance. Linearity is 1.5 to 2.5 dB better with the
W-CDMA signal.
LTE provides users with very high
data rates in mobile devices enabling
streaming multimedia and supporting
the growth of social networking and
the push to cloud computing. LTE
imposes unique system requirements
and presents challenges to the power
amplifier designer, particularly of the
downlink. RFMD has developed a
family of products to address these
needs. They cover the key downlink
frequency bands, provide an ACLR of
better than -44 dBc and provide efficient operation with LTE modulation
bandwidths of up to 20 MHz.
RF Micro Devices,
Greensboro, NC
(336) 664-1233,
www.rfmd.com.
MOBILE COMMUNICATIONS n NOVEMBER 2011