Cover Story
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Flat gain is hard to come by in any
amplifier especially one with even moderate bandwidth. Achieving flat gain requires that the amplifier’s active devices
are impedance matched as closely as
possible for all of the frequencies within
that bandwidth. Since most transistors
exhibit extremely low impedances, designing a matching circuit to serve as an
interface to the “outside world” at 50 Ω
for any appreciable bandwidth requires
tradeoffs, such as sacrificing some gain
or noise-figure performance in order to
achieve flat gain with frequency. For ex-
1. The YSF-122+ and other members of the YSF Flat Gain amplifier family are supplied in
a plastic surface-mount package measuring just 5 x 6 mm complete with input and output
ports matched to 50 Ω.
The YSF Flat Gain amplifiers at a glance
Model
Frequency
range
(MHz)
Gain
(dB)
Gain
flatness
(dB)
Noise
figure
(dB)
Output
power
(dBm)
YSF-122+
800-1200
20.4
±0.2
3.4
+20.5
YSF-2151+
900-2150
20.0
±0.4
3.1
+20.0
YSF-162+
1200-1600
20.1
±0.2
3.2
+20.0
YSF-232+
1700-2300
20.0
±0.2
2.8
+20.0
YSF-272+
2300-2700
19.0
±0.7
2.5
+20.0
YSF-382+
3300-3800
14.5
±0.9
2.5
+20.0
YSF-322+
900-3200
17.0
±2.2
2.5
+20.0
Notes: Values shown are typical, with gain, noise, figure, and output power at 1-dB compression values
measured at midband frequencies and typically +5 VDC and 145 mA.
100 January 2011| Microwaves&RF
23.0
22.5
22.0
21.5
21.0
20.5
20.0
19.5
19.0
18.5
18.0
–45°C
+25°C
+85°C
800
850
900
950
1000 1050
Frequency—MHz
1100
1150 1200
2. The small-signal gain for the YSF-122+ amplifier, which is nominally 20 dB, is plotted versus frequency at three different operating temperatures.
40A_F2
ample, developing amplifiers capable of
reasonable flat gain and low noise figure
usually requires sacrificing output power
and dynamic range (as characterized by
third-order intercept point). Building
an amplifier that has high, flat gain, low
noise figure, and even moderate output
power at 1-dB compression calls for clever impedance matching across the full
operating frequency range.
That is precisely what has been done
in the YSF series of Flat Gain amplifiers.
They are impedance matched across the
frequency range specified for each model
and provide a unique combination of high
gain, flat response vs. frequency and also
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
850
900
950
1000 1050
Frequency—MHz
1100
1150 1200
4. The noise figure of the YSF-122+ amplifier remains stable even
with changes in bias.
40A_F4
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+4.75 VDC
+5.00 VDC
+5.25 VDC
800
850
900
950
1000 1050
Frequency—MHz
1100
1150 1200
40A_F3
relatively low noise figures and outputpower levels that are typically in the range
of +20 dBm—much higher than other
commercial amplifiers that are nominally
considered low-noise amplifiers (LNAs).
The YSF amplifiers leverage a mature
GaAs enhancement-mode pseudomorphic high-electron-mobility-transistor
(E-pHEMT) integrated-circuit (IC) process that has been well characterized to
better understand its electrical characteristics over frequency and temperature.
This process, and the intelligent design
of these two-stage, medium-power amplifiers, contributes greatly to the stable
frequency response over temperature
+4.75 VDC
+5.00 VDC
+5.25 VDC
800
23.0
22.5
22.0
21.5
21.0
20.5
20.0
19.5
19.0
18.5
18.0
3. The small-signal gain for an YSF-122+ amplifier is plotted versus
frequency at three different bias settings to show insensitivity to
supply voltage.
Gain—dB
ning a total frequency range of 800 to
3800 MHz with typical gain of 20 dB and
typical gain flatness as good as ±0.2 dB
across a 400-MHz bandwidth.
Gain—dB
ain flatness control plays
an increasingly important
role in modern communications systems, notably those
that rely on multiple gain stages and
high-gain intermediate-frequency (IF)
amplifiers. Key receiver components,
such as amplifiers and filters, typically
exhibit variations in gain or amplitude
response, presenting challenges for
designers working with modulation
schemes such as quadrature amplitude
modulation (QAM). However, with the
launch of the YSF series of “Flat Gain”
amplifiers from Mini-Circuits (www.
minicircuits.com), extremely well-controlled amplitude responses are now
available in a line of amplifiers span-
Noise figure—dB
These easy-to-use
plastic-packaged
amplifiers provide
high, flat gain
for small-signal
applications through
3.8 GHz, including in
satellite and cellular
communications
systems.
Amps Aim at Flat Gain
G
Gain—dB
Technical Director
(temperature and full characterization
data for all of the YSF series amplifiers
can be found on the Mini Circuits web
site at www.minicircuits.com).
As an example, model YSF-122+ is designed to cover the full cellular communications L-band of 800 to 1200 MHz . As
with other members of the YSF Flat Gain
amplifier family, it is easy to plug into a
design: the amplifier has 50-Ω input and
output ports, includes internal feedback
and bias circuitry, and operates from a
single positive voltage supply. No additional external components are required.
As with the other YSF amplifiers, the YSF122+ is a Mini-Circuits System-In-Pack-
23.0
22.5
22.0
21.5
21.0
20.5
20.0
19.5
19.0
18.5
18.0
+4.75 VDC
+5.00 VDC
+5.25 VDC
1700
1800
1900
2000
2100
Frequency—MHz
2200
2300
5. The small-signal gain for an YSF-232+ amplifier is plotted versus
40A_F5
frequency at three different bias settings.
101
age (MSiP) module that is housed in a 5
x 6 mm plastic package. This is an eightpad package (Fig. 1), although only three
pad connections are needed: for bias, RF
input, and RF output. The other five pads
are not used. The housing includes input
and output DC blocking capacitors.
The YSF-122+ pHEMT amplifier is
ideal for applications where a small gain
block can be added to overcome the signal losses from passive components in a
system, such as filters, cables, or switches. It provides nominal gain of 20 dB with
±0.2 dB gain flatness across its 400-MHz
bandwidth. The small-signal gain is typically 20.1 dB at 800 MHz, 20.4 dB at 1000
MHz, and 20.3 dB at 1200 MHz.
The gain remains flat even across its
specified operating temperature range
of -40 to +85°C (Fig. 2). The amplifier’s
gain was characterized at room temperature (+25°C) as well as near the extremes
of the operating temperature range (-45
102 6. The small-signal
gain for an YSF-382+
amplifier is plotted
versus frequency
from 3300 to 3800
MHz at three different bias settings.
Gain—dB
flat-gain amplifiers
22
21
+4.75 VDC
20
+5.00 VDC
19
+5.25 VDC
18
17
16
15
14
13
12
3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
Frequency—MHz
40A_F6
and +85°C). The measurements
reveal
the expected drop in gain at the hightemperature extreme, and the increase in
gain at lower temperatures although, as
the plots show, the gain across frequency
at all three temperatures tracks closely
and remains consistent across frequency
and temperature.
The gain-versus-temperature-and-frequency measurements were performed
with a bias supply of +5 VDC and input
power of -25 dBm (the model YSF-122+
amplifier is rated for maximum input
power of +21 dBm). When the YSF-122+
amplifier’s small-signal gain was measured as a function of several different
bias voltages above and below the nominal recommended +5-VDC bias level, the
gain also remained remarkably flat (Fig.
3), showing the amplifier’s relative insensitivity to variations in supply voltage.
In addition to its extremely flat gain,
the YSF-122+ amplifier excels in other
parameters not typically associated with
high, flat gain, including noise figure,
output power, reverse isolation, and output third-order intercept (IP3) performance. The amplifier exhibits noise figure of 3.5 dB at 800 MHz, 3.4 dB at 1000
MHz, and 3.4 dB at 1200 MHz. As with
the gain, the noise figure for the YSF122+ amplifier is very well behaved with
bias supply. When characterized at bias
settings of +4.75, +5.0, and +5.25 VDC,
the noise figure remained close to 3.5 dB
across all frequencies of operation. And
even across the operating temperature
range, where the noise figure of an amplifier is expected to fluctuate, the YSF122+ shows only about ±0.5 dB variation
(Fig. 4).
The YSF-122+ also delivers typical
output power at 1-dB compression of
+20.5 dBm at midband, with levels of
+20.5 dBm at 800 MHz, +20.5 dBm at
1000 MHz, and +20.4 dBm at 1200 MHz.
The output IP3 performance is typically
+37 dBm at 800 MHz, +36 dBm at 1000
MHz, and +36 dBm at 1200 MHz. The
reverse isolation is typically 32 dB, while
the midband input return loss is typically
11 dB and the midband output return loss
is typically 15 dB. The amplifier typically
draws 118 mA from a +5-VDC supply.
January 2011| Microwaves&RF
flat-gain amplifiers
In spite of its
broad bandwidth,
the YSF-322+
achieves low
noise figure, with
typically 3.0 dB at
900 MHz and 2.5
dB at 3200 MHz.
The YSF-122+ is just one
example of the Flat Gain
amplifier product line,
with additional models
providing various bands
of coverage through 3.8
GHz (see table), including model YSF-232+ with a
bandwidth of 1700 to 2300
MHz that is well suited to
many cellular communications applications and two
relatively broadband models, the 900-to-2150-MHz
model YSF-2151+ and the
900-to-3200-MHz model YSF-322+.
The YSF-232+ maintains impressive
±0.2 dB gain flatness for typical gain of
20 dB across the 600-MHz bandwidth
from 1700 to 2300 MHz. At room temperature, the gain is typically 19.8 dB at
1700 MHz, 20.0 dB at 2000 MHz, and 19.5
dB at 2300 MHz. The output power at
1-dB compression is typically +20 dBm
at all three test frequencies, with IP3 of
typically +35 dBm at all three test frequencies. As with the lower-frequency
YSF-122+, the YSF-232+ maintains remarkably flat gain across the frequency
range even with fluctuations in the
supply voltage (Fig. 5). The YSF-232+
amplifier has typical midband noise figure of 2.8 dB and typical reverse isolation
of 30 dB.
For general-purpose, broadband satcom applications, the YSF-2151+ amplifier has typical specified gain flatness of
±0.4 dB from 900 to 2150 MHz (Fig. 6).
It supplies typical gain of 20.2 dB at 900
MHz, 20.0 at 1600 MHz, and 19.8 dB at
2150 MHz. The output power is +20 dBm
at all three test frequencies, and the noise
figure remarkably drops with increasing
frequency, registering 3.5 dB at 900 MHz,
3.1 dB at 1600 MHz, and 2.6 dB at 2150
MHz. The YSF-2151+ has high reverse
isolation of 30.5 dB with typical current
draw of 118 mA at +5 VDC.
The broadest-bandwidth YSF amplifier is model YSF-322+, with 20 dB typical
gain at 2000 MHz and a usable bandwidth
of 900 to 3200 MHz, although gain does
drop off to typically 16 dB at the upper104 frequency limit. As a result of the wide bandwidth
covered, this is the YSF
amplifier with the poorest gain flatness, at ±2.2
dB, although still competitive performance for such
a wide bandwidth. In spite
of the broad bandwidth,
the YSF-322+ achieves low
noise figure, with typically
3.5 dB at 900 MHz, 3.0 dB
at 1700 MHz, 2.5 dB at 2500
MHz, and 2.5 dB at 3200
MHz. The output power at
1-dB gain compression is +20 dBm at all
four test frequencies, while the typical reverse isolation is a robust 30 dB.
The highest-frequency YSF amplifier
is model YSF-382+, which covers 3300
to 3800 MHz. The gain drops off somewhat compared to the other members
of the Flat Gain family, 16.0 dB at 3300
MHz, 14.5 dB at 3600 MHz, and 14.0 dB
at 3800 MHz, but the gain response is still
a respectable ±0.9 dB in terms of flatness
with frequency (Fig. 6). The noise figure
is typically 2.5 dB at 3300 MHz, 2.5 dB at
3600 MHz, and 2.6 dB at 3800 MHz, while
the output power at 1-dB compression
is typically +20 dBm at all three test frequencies, and the output IP3 is typically
+36 dBm at all three test frequencies. The
YSF-382+ exhibits 28 dB typical reverse
isolation for good immunity from signal reflections in the signal-processing
chain, such as from reflective filters.
The YSF Flat Gain amplifiers are designed to handle maximum input-power
levels to +21 dBm and are supplied in
eight-lead 5 x 6 mm plastic surfacemount packages with a conductive metal
paddle for dissipating excess heat. All of
the E-pHEMT amplifiers are two-stage
designs that operate from a single +5VDC voltage supply and all feature input and output ports matched to 50 Ω
for ease of use. Full data sheets, performance curves, and raw data are available
on the Mini-Circuits web site. —JB MiniCircuits, P. O. Box 350166, Brooklyn, NY
11235-0003; (718) 934-4500, FAX: (718)
332-4661, www.minicircuits.com. MRF
January 2011| Microwaves&RF