EE-940 Advanced RF Measurements
Submitted To:
Dr. Nosherwan Shoaib
Submitted By:
Engr. Irfan Mehmood
A SUMMARY OF TESTING RF POWER AMPLIFIER DESIGNS
The main focus of the webinar is on the testing of power amplifiers. The process flow
involves starting with research and design phase. This phase is started simulation and
emulating the power amplifier design. Then after getting the hardware in the lab, the
characterization process can be started. In this phase highly accurate and flexible test
and measurement solution is required. The complete desired RF performance is
achievable once the complete behaviour and characteristics of the device under test
are finally known.
Usually when there is new emerging technology coming in, like we are going into
higher frequencies and other upgradation in the hardware, then largest dynamic range
is required to know the true capabilities of the new technology. When the device gets
ready you want to test how it performs over temperature and frequency variations.
This all involves characterization processes.
Large measurements are done and not only on a few devices but on large number of
devices before finally putting the device under mass production. In this process it is
ensured that all requirements are met before releasing the design to production
In production, it is to be ensured that the device really meets the specifications and it
is shipped as a good device to the customers.
After starting with R&D through the different process flows, performance optimization
is done. This can be done with different techniques, different topologies for amplifier
as well as with linearization to get better performance. All this involves different testing
scenarios.
Discussing the design phase, Cadence software is used in which demonstration of
device is shown in the middle of the top window. At right and left, different blocks of
R&S are present. These blocks act as data sources and data sinks. These enable the
ability to send or get signal from R&S hardware to simulation and back again. All this
is possible as R&S has developed all different digital standards.
WinIQSIM2 tool enables the creation of signals of various standards from 5G to WiFi
and many others. These signals can be transferred into the Cadence Visual System
Simulator (VSS) which is being used for different blocks in the design. The result is
then transferred over to R&S VSE (Vector Signal Explorer) which is a signal analysis
software where you can have a look at the modulation performance going through the
complete simulations.
An early understanding about the linearization capabilities of your design can be done
as well. As it adds the ability to run a direct DPD linearization in conjunction with the
simulation.
In the simulation phase, it is understood how does this correlate to real hardware
measurement. WinIQSIM2 as well as VSE is used conjunction with the Cadence
software, and those two tools, WinIQSIM2 and VSE, are using the same calculation
methods, the same algorithms as used inside of the instruments, (Inside of a vector
signal generator and a vector signal analyzer). There is already a direct correlation
given by using exactly the same methods. And you can basically replace then the
simulated world with the real hardware.
Now for the real hardware verification and characterization, there is a lot of topics to
be measured to be addressed. And ideally, we want to have one tool to measure as
much as possible in order to simplify the testing process.
There is a long list of different RF parameters from frequency coverage to power
consumption, to understand the gain, the amplification characteristics, all the way to
noise figure.
All of these can be done with just one tool, a vector network analyzer. Many of those
items are directly derived from S-parameter. And S-parameter is the basic
measurement a vector-network analyzer does.
When we look at compression point and power-added efficiency, what is the
measurement we want to do here?
We want to understand the maximum output power versus the useful power range.
Why do we differentiate? Because the maximum output power is already way into
saturation. We see already very large non-linear effects. And typically what is
characterized is to say what is the 1 dB compression point? Meaning how far can we
use the amplifier in the linear way before it really goes into compression.
And typically, a 1 dB compression is shown as a threshold here. There are also others
which are using 3 dB compression point. So, this is freely definable and, in the end,
dependent on the target application.
A VNA with its power sweep can easily do that measurement by sweeping the input
power and measure the result on the output side. Ideally, this is done with a power
sweep moving up and going down to understand the history of the design of the
amplifier because there can be a different performance like a different characteristic
in the power transfer function. Another factor is Power-added efficiency(PAR) that is
to understand what is the power consumption at a certain output power, at a certain
gain.
This is a similar measurement for the VNA point, but we have to add also the capability
to measure the power which is going into the device as the power consumption as the
power supply basically. And we are taking the relationship between the output signal
and the input signal and take this relative to the power provided to the amplifier.
Another important point for amplifiers is the intermodulation.
An amplifier has non-linearities, and typically there can happen different
intermodulation when we have a two-tone signal or any type of scenario. Typically for
intermodulation, a two-tone scenario is used. There are different methods. Two-tones
are used, and then you want to understand the behavior across frequency, across
level.
What is offered or what is performed typically is to use a two-tone and step this over
the frequency range shown in the plot. The other thing is to keep one tone static and
just move the second to go right and left to change the offset or variable spacing, as it
is called here. The third one is to keep this position in the frequency range constant,
but we also have one tone fixed and the other one changing in its power going up and
down to see the effect of the non-linearity in the intermodulation.
In a network analyzer, this can be done all in a very quick manner with dedicated tools
to run those intermodulation measurements. What is required to do so are different
sources in the analyzer to generate the two-tone signals, and ideally to have an
internal combiner so that one output port of the vector analyzer already gives you the
sum signal and you do not have to use an external combiner where additional
calibration is required.
Another important measurement to understand the linearity of the amplifier is called
the intercept point measurement. It is often called IP3, intercept point, third order, or
TOI, third order intercept.
It all describes basically the same. It's a mathematical approximation of the
comparison between the linear behavior as well as how fast the third order harmonic
is increasing. And typically, this is not a measurement which can be done directly on
the point, but it is really a mathematical, a theoretical point based on the crossover of
the wanted curve, of the wanted gain translation shown here in blue, and the red curve,
which basically shows how the third order harmonic is increasing with higher power.
The harmonic is increasing faster at a certain output level, and this way it creates a
crossover point. And the further out this is, the better the characteristic of the amplifier.
Another topic is the harmonics. You basically just run a CW signal into the PA and you
measure all of its output. Within a vector network analyzer, you can use a frequency
conversion measurement method because you know exactly where the harmonics are
at the second, the 2x, 3x, 4x, and so on. Now, we are now at the target frequency of
the original input frequency. This can be easily done using frequency conversion
measurements. When you want to look at, are there any other spurs around.
Well, then a spectrum analyzer mode in the VNA comes very handy because this gives
you the full spectrum view and you can see if there are any other spurs out there.
In intermodulation measurements step, we've actually connected the device under
test, our amplifier, and now we're going to configure the intermodulation
measurements and look at the performance of our DUT. We can see that the two tones
now are at a much higher power level because we've got the amplification of the device
under test, about 25 dBs.
In the top window, what we're going to do is add measurement quantities. Back in the
measurement menu, we can see underneath the wizard, we have the measurement
parameters. We'll start with main tone, where we can look at both the lower or the
upper tone reference to the input or the output of the device under test. Here lower
tone is chosen. We have the intermodulation products. You can see all the relevant
products are displayed here. In this particular example, I'm just going to choose a third
order lower tone. Then the intercept points shows in exactly the same way.
In the scale menu, we can auto scale all of these to a common scale. Let's just
maximize that. For ease to be able to read off the values, let's just put a marker on
here. Now we can see that at this particular frequency, see, around 3.75 gigahertz.
We have a third order lower tone of intermodulation that's around about -35 dB. Then
from that we can calculate the intercept point in this particular case, then at around
about 38 dB.
Another very important characteristic of a power amplifier or also of a low noise
amplifier is the noise figure, or also called noise factor in the linear world.
The noise figure basically describes the added noise by the amplifier itself. Let's have
a look at an example. On the bottom left, you see an input signal with a certain signal
strength, and there is always some background noise. Now, when this signal goes
through the amplifier, everything is amplified with the gain of the amplifier. So the signal
is amplified, as well as the wideband noise. Unfortunately, the amplifier itself also adds
some wideband noise. This results in a limited dynamic range, limited signal-to-noise
ratio, shown on the right plot with the red arrow showing that the signal-to-noise ratio
is a certain way reduced compared to the input signal. Obviously, this should be as
small as possible. The added noise by the amplifier should be as small as possible,
and especially when we are talking about low-noise amplifiers, often used in the
receive path of an RF design. The noise figure should be as low as possible. What we
need to understand for the noise figure when we have to measure it, we basically look
at the output noise versus the input noise in conjunction with the gain, as shown also
in the formula of the noise factor shown here in linear terms.
To measure it, we can use two different approaches. One is with a spectrum analyzer,
the other one with a vector network analyzer. Let's have a quick look how to do this
with the spectrum analyzer. There we use also a noise source which is very well
characterized and we know exactly what noise comes out when we turn it on or we
have it off. It's also a component which is in the loop and we connect it to the device
under test, as shown here on the plot. And we make a measurement of the noise
coming from the device under test after amplifying the noise from the noise source or
having the noise source turned off. And when we take those two measurements into
account, you can draw the graph as shown here on the bottom right. And taking these
two measurements, you can take a line through it and can in this way also calculate
back, derive the noise added just by the device by the amplifier. There is also an
application node referred here giving you more background information on this. The
second method typically used with a vector network analyzer is called the cold source
method.
We are using here the vector network analyzer as a source as well as a measurement
receiver and measure noise while the source is turned off and measure gain while the
source is turned on. The calculations are based on noise-temperature representation,
meaning we are looking at not the noise each component adds to it, but the
temperature, which is the corresponding effect to it. Also, easy to remember cold
source method, looking at temperature representation here. And what is important to
have really accurate measurement results and also repeatable data is a good
calibration of the vector network analyzer. Meaning the calibration of the noise
temperature of the source on the left side and the receiver on the right side. And then
you see here the formula through which you can derive the noise factor. Now, when
we look at physically how to connect to the device, it really depends on the stage of
the device. There you want to do probably already the first different characterization
before putting it into different dyes, sawing it, separating the different modules, and
packaging it. The first step typically is on wafer testing and wafer verification.
Focus for this is at first to understand that the wafer run really was successful and is
working as expected. This is typically done using DC, so voltage behavior, as well as
some basic RF parameters. This is done together using manual or different stages of
automation, wafer probers, in order to connect to the DUT on the wafer. When you
want to make measurements and, on an amplifier, typically the amplifier gets warm
when it's being used. And when you think about the amplifier in a full stage, there is
some cooling. Obviously, on a wafer, there is no possibility for cooling. So we need to
take care on the signal path already not to overheat the device. And that is why we are
focusing not on standard S-parameters, but on pulsed S-parameters in order to limit
the self-heating of the device. The other topic is when we look at on-wafer, typically
there is no matching network around it. So load-pull meaning to optimize to set a
certain impedance on the input and on the output may be important. Very often on
wafer testing is done in combination with load-pull measurements.
In the end, you can use tuners in a classic load-pull design to create a certain
impedance on the input and on the output. They are typically used in between the
vector network analyzer of a test instrument and to the device on the test. There can
be different methods as passive and active load pull. It is important to understand here
why we want to use it because the transistors, the core of our amplifier, are highly
dependent on its load impedance, on the input, or on the output. Load pull allows us
to basically provide any an impedance to the device and the test we want and to
understand the behavior across different impedances, but also to match to a 50 Ohms
world.
Unfortunately, in this area, small signal characterization of the PA is not valid anymore
because of non-linear effects, the behavior changes. But we still can measure with a
VNA director wave quantities describing the performance and the characteristics of
the device.
And also similar to on wafer testing, a raw PA dye and also the insert of an MMIC are
typically not 50-ohm devices. But the whole world and all the RF design is typically
based on a 50-ohm design. There is a matching network required. In order to
characterize the device. Another topic is you need to design a device model. We talked
in the very beginning about simulation and design early phases. Well, when you take
the PA into a larger environment, into a complete RF system, and you are starting to
simulate this, you need a good model for the amplifier.
There are two methods to calculate those. One is called a compact modeling
approach, where you are basically measuring small signal effects. You're looking at
the linear behavior, you describe this, and you create a model based on the behavior,
meaning, Oh, there is a certain capacitance effect here, there is a resistance here, and
you create a model as shown here, for example, in this fat compact model. The other
approach is called a behavioral model. We are looking at the PA in this way as a black
box. And we just want to describe the transfer function from the input to the output and
don't want to go into the detail of the different effects inside of the transistor as before.
This approach also takes into account harmonics and different impedance effects. So
what we derived before from load-pull measurements. And it's typically measured with
a non-linear vector-network analyzer approach and also works not only for the linear,
but for the non-linear range of the device under test. And there are different systems.
Another term which is often used in the industry is called X-parameters, which in the
end is just another term for PhD behavioral model. Now we want to transition from
CW-based measurement to modulated measurements to modulated scenarios. Why?
Within the traditional approach, using a VNA for CW measurements, you can get a lot
of information and characteristics out of the device. But when we look at really
wideband modulation schemes, as we see today with 5G, ultra-wideband, or the latest
WiFi additions. You have a high band with a couple of hundred megahertz, sometimes
even up to gigahertz range. And then the behavior of the amplifier, not exactly can be
modeled, can be verified with just CW testing. Ideally, you really want to use the target
scenario, the target signal, in order to understand the behavior of your device. The test
setup typically looks like this shown here, where we use a signal generator, a vector
signal generator with the wideband modulation capabilities and a spectrum analyzer
on the other side, being able to demodulate. In order to get really accurate power
results and also gain measurements, you combine this also with power meters, input,
and on the output side.
The signal-to-noise ratio of the device. So if we are talking about really high power
levels, we are getting close to the saturation point of the amplifier and see some
compression. So, the performance is not as good anymore and we see an increase of
EVM. Below this, it's the ideal section where we have the best-performance EVM, and
that should be ideally as wide as possible. On the lower end, we see already that the
signal-to-noise ratio is degrading based on lower input powers, based on also lower
signal levels. And this also EVM increases again. And that's why it's called this bathtube curve. Last but not least, distortion measurements we mentioned also already on
the VNA side with CW approaches where you basically sweep the CW tone through
the input to do AM to AM distortion or AM to PM distortion, so amplitude distortion or
phase distortion. In a modulated world, we do not have to sweep the input power, but
we can make benefit of the signal fidelity due to its modulation. And while just capturing
a certain time duration, we typically have a large variance on the power levels and a
nice distribution and can directly derive from there also the AM to AM and AM to PM
curves as shown here in these plots.
Also, a common scenario is to use different typologies. For example, envelope
tracking, Do-R-T scenarios, Do-R-T amplifiers. Or just lately, they are starting to look
more and more into load modulated balanced amplifiers, L-MBAs in short. And not to
forget linearization, which can be done, for example, with digital predistortion. When
we talk about waveform engineering, we're basically talking about different amplifier
classes like Class A, class B, et cetera. It is defined by the time duration it is conducting
power and the longer the conduction angle, so the time it is conducting power, is the
more linear the amplifier acts, but the lower the efficiency is. We see this in the table
below. And on the right side in the diagram, we see the different classes and its
duration, conduction angle based on a sinusoidal input. Another optimization method
is crest factor reduction. Crest factor describes the ratio between the peak and the
average power in the signal. As we see on the CCDF, those peaks are pretty rare, so
they are not coming that often. But in order to transmit the whole signal very linear, we
need to keep those peaks still in the linear range of the amplifier.
On the downside or as a challenge, we really need to have a high-speed tracker, which
is typically somewhat in the range of three to five X the signal bandwidth. So, when
we talk about high-speed signals with 100 megahertz, we need a tracker which is able
to follow that at a rate of 300 to 500 megahertz. Very commonly used in, let's say, on
infrastructure scenarios is a Dorothy amplifier. It is already invented a long time ago,
but it's a very well-known and very well-researched efficiency enhancement method.
It is also combining two amplifiers. One is used for the main, so basically for the R-MS
power, and the other one is used for the peak power. As we have only RMS, we don't
really care for those high peaks we talked before on the crest factor reduction, we can
use this closer to saturation in order to get more efficiency out of it and leave the
auxiliary amplifier with a larger headroom for the peaks. And this one is then also
trimmed for more linearity. And in this way, typically there are uses of different amplifier
classes.
Typically, these are using a differentially biased devices with different behaviors. The
other side is the digital Dorothy. In this way, we are not having one, but two different
channels driving the amplifier. So we split the signal not analog, but in the digital
domain already. And drive in this way already two separated signals to the main and
to the auxiliary amplifier. In this way, we can better optimize the signal behavior and
better position the amplifiers used in conjunction together, and this creates better
efficiency.
We are splitting the signal digitally and manipulate the phase and the amplitude
between the two channels and create measurements to see where is the best point in
collaborating between the two amplifiers. This can not only be done for saturated
power, but obviously also for efficiency, ACLR, and any other matrix you are interested
in. Unfortunately, what is best for efficiency is typically not best for saturated power,
typically not best for ACLR. But with these measurement campaigns, you know exactly
when you put a splitter at a certain position, what you're getting out of this. Based on
the usage of the Dorothy design, you can optimize your overall design by selecting
based on all those measurement data and you know exactly what you're getting. Let
me show you here a possible outcome of a Dorothy design with a conventional mode
of operation shown on the left, and even a dual input mode operation where we are
using the Dorothy design really in its best possible way. What you see in the two plots
is the gain compression on the top and the phase variance on the bottom. Ideally, on
the phase variance, you want to have it as flat as possible.
And on the gain compression, you want this to be put out as much as possible. So,
you want to have a linear behavior as long as possible. And the dual input mode shows
you more than a DB of extending the capabilities. This enables you to say, Well, I can
better spec my device, or I can take a different device with the same setup and a
smaller device, so to say, and save energy, save power in this way, also save cost.
Another possibility would be, I leave the specifications as they are for performance,
but extend the bandwidth over which they are possible. Talking about increasing
bandwidth over which a certain performance is possible, that is also one reason why
more and more are starting to look at load-modulated balanced amplifiers. It's a new
topology where typically, again, two amplifiers are used in a balanced performance or
two balanced amplifiers, plus control signal power, which is injected on the output,
which is creating our load modulation, so to say. And this concept offers really large
bandwidth coverage, even all the way up to 100 %. Unfortunately, the power which is
coming in from the CSP port is going directly through and needs to be very linear.
So, it has a high requirement on that CSP input. It is already started to look at a variant
of the L-MBA, which is called an orthogonal L-MBA. And this uses a different input for
the control signal, not on the load side, but also on the input side on the left, so to say.
And adding a fixed or a tuned load on the output. This enables a more efficient usage
of the L-MBA structure. Obviously, the tuned load on the output can also be used for
large variants, also for measurement campaign in order to best understand what
should be used there, also created by an active load modulation. Okay, so much about
the different topologies. Let's have a look at linearization methods. And again here,
there's a lot of research in there. The target, what we want to reach for linearization is
to have it as linear as long as possible. Am to AM should be really like a flat line until
we hit something like a brick wall. So it doesn't get any further. We are really at the
saturation point at the amplifier. And the AM to PM, also there is no distortion. So again,
here a flat line.
Different methods are out there: Cartesian polar feedback, analog digital predistortion,
and feed-forward. A lot of them have been researched. I want to focus here then a little
bit more on the digital predistortion because this is what is used very commonly
nowadays. The benefit of having digital predistortion in such a scenario is also that it
allows us to use more variants and more flexibility on the typology. Because some of
those topologies, including LNBA, show certain interesting special behavior when
transmitting a signal, and these can be compensated with the two predistortion. There
is a close collaboration ideally given between those two in order to get best efficiency.
So predistortion really is done in a way to compensate the DUT performance, the DUT
characteristics. In the plot here, we see with blue, the performance, the classic
compression curve of an amplifier. Red is what we would like to see, and with those
orange dotted lines, we see the DPD-manipulated input signal in order to compensate
for the distortion for the saturation of the amplifier. So, if we want to use an amplifier
close to compression where efficiency is highest, but non-linearity also is highest, so
we need to compensate, we need to use any linearization.
Ideally, when you're designing a PA, you want to understand how well you can linearize
this. How good can my PA behave with a EVM characteristic or with ACLR when we
have proper predistortion? Typically, predistortion is not the main skill set in this
environment when we are designing amplifiers, but we need to understand it. Direct
DPD, as we offer this in our systems, in our instruments, gives you an easy way to
understand how good an amplifier can behave with an ideal predistortion by basically
manipulating the input signal in an iterative process and comparing the output signal
when it comes from the device under test here on the right side, comparing here with
the input signal and what is the variance and manipulating sample by sample the input.
In order to create a pre-distorted signal. This is done in an iterative process and
optimizing the signal.
We even have a hard clipping. This can have two effects. It can be a configuration of
the direct DPD configuration, or it can be simply the saturation point of the power
amplifier.
Now, let's move on to device characterization. In R&D, we were looking and testing
four design goals to reach the design goals. In characterization, we want to ensure
that not only one device or a small sample meets the design goals, but a larger sample
before we will release the product for production. What we are looking here for is to
verify to verify on a larger scale, on a larger number of samples, and to verify also the
data sheet performance figures, and even more. To better understand the
characteristics of the device over frequency, over level, and also over temperature.
So, it's a larger measurement campaign which is typically fully automated. And it also
includes to get a certain of lifecycle testing included to understand the durability of the
design. The test requirements for the RF characteristics are basically very similar to
what we've done already in research and design. Now, in characterization, we are
looking at the same RF matrix as in research and development. And this way also we
need a similar test setup from the function block point of view. Here we show on the
plot a network analyzer to do CW measurements, to do also matching measurements.
And on the other side we have a signal generator, vector signal generator and vector
signal analyzer for the modulation measurements. And obviously also a power supply
which is also able to measure the power consumption going into the device for
efficiency measurements. Active devices call for a diversified characterization using
CW and modulated tests. And typically, they are done, as shown on the last slide, with
different instrument setups: vector network analyzer or vector signal generator, vector
signal analyser on the other side. And both have their pros and cons and their
strengths, their individual strengths. In a complete characterization setup, sometimes
even both sides are used or often even both sides are used. And in this way, then
there might be a change in connection by a standard setup or a switching in between
them. Not ideal. The goal should be to have one connection and run all the different
testing. That also enables you to run the testing in a faster, smoother way with a higher
measurement speed because we are doing a large measurement campaign and
typically this can take quite some time. Using a calibration, as we use in the VNA also
for the modulation part, would give us also more accuracy on EVM with something
which is called a vector-corrected EVM.
And in this way, it is also optimized with one connection for automated testing because
there is no manual needed. So how can this look like? What we are proposing here is
a combination of the setup with the signal generator on the left, signal analyzer on the
right, and the VNA at the bottom. The connection between them is using a coupler.
And once everything is calibrated, you can run all the different measurements in an
automated setup with the individual instruments with best characterization capabilities
as we have calibrated out the effect of the coupler all the way down to the DUT port,
not only for the VNA, but also for the signal generator and analyzer. So basically, one
can say the effect of the measurement setup is de-embedded by using the proper
functions inside of the signal generator and analyzer, which offer this ability for deembedding. In lifecycle testing, typically we do also stress testing using defined Halt
techniques, highly accelerated lifecycle tests, as they are called, doing stress with
vibration, temperature, humidity, but also with a high input power. What we are doing
is we are increasing the stress gradually and check the performance of the PA.
This on one side helps to understand what can be done or how long can it sustain it.
But on the other side, it also derives the ability to understand the behavior of the PA
before it breaks. This enables also to add a warning system, a monitoring system in
an overall system based on knowing, okay, if a biasing point is changing with high
power or over time, this will indicate the end of the life cycle of the product. As a next
step, we want to look into the production requirements. Well, in production, it's not
really about measuring accurately each component. It's about ensuring proper
functioning of the components and meeting the target specifications. While the focus
is on the throughput and on the speed of measurements for reducing the cost. And in
this way, repeatability from one sample to the next is more important than absolute
level accuracy or absolute measurement accuracy. Testing and production is typically
done in two different stages. At first, testing is done on the wafer level, where we want
to make sure that the wafer run is successful before we spend the additional money
for dizing it, putting it into dice, and even packaging for final testing.
And then this is the full RF testing in the package device typically conducted. The test
procedures which are followed are often based on the characterization testing. What
we are doing is we don't want to go obviously through the full process, but it's a very
much limited set of characterization tests which is also used in production. So, where
we are looking at critical performance points as well as also classic analog and digital
behavior of a MMIC, for example. So, we want to understand at a certain output power,
what is the power consumption? And if those two matches to what we learned in
characterization, what a good device performs, then we know that this device works
and is according to specifications. Parallel testing is an important topic in order to
increase throughput by using multiple devices at the same time. Multiport test
instruments, like shown here, a multiport vector network analyzer, enable really
multisite test in parallel as they are offering multi-receive passes or multi-transmit
passes in one instrument. It's not a switched approach where one after the other is
done, but it's really testing in parallel in order to improve the throughput. In contrast to
in characterization, in production typically, we want to focus on CW-only or modulationonly approaches.
There is no combination typically between VNA as well as modulation setup, but just
one or the other in order to simplify the test setup and also to reduce cost. An important
point in production is that typically we have also load boards and we have more signal
conditioning in between the device and the test towards the input and to the output
through the measurement receiver. So, calibration all the way down to the DUT is an
important topic and also to run some de-embedding of those effects. And the absolute
accuracy is really just based on the calibration of the whole system. One downside
which typically comes in with longer cables, longer signal routing, is that we are losing
power there, unfortunately. We have signal losses, signal attenuation. And that means
we are losing dynamic range. So, it's a balance. What we need to cover with
measurement accuracy, what is needed, and also to still have enough signal-to-noise
ratio to meet those measurement accuracies. But on the other side, to minimize the
cost by taking, let's say, a more economic version of what was used in R&D, for
example. And that's why really repeatability and reduced measurement uncertainty is
important here in this way and unfortunately, higher output power or sensitivity can
cope with this.
There are various amplifier topologies out there, but in general, the different process
steps in research and development, in characterization and in production are pretty
much the same, no matter if we are talking about a CMOS-based amplifier or a gallium
nitrite-based amplifier. The combination of CW and modulator testing gives us the
most comprehensive understanding of the performance of the device. And obviously,
special scenarios based on the application of the device are typically coming in in order
to ensure proper functioning, best efficiency, best fitting into the target application. Last
but not least, linearization, post-digital predistortion, for example, is an important point
as it helps us to get more efficient designs using amplifiers closer to its compression
point, but also to offer a wider range of possibilities in order to optimize the amplifier
topologies by using different linearization techniques. And this gives us a more
freedom in the PA design.
Reference:
Webinar:
A
summary
of
testing
RF
power
amplifier
designs
https://www.rohde-schwarz.com/us/knowledge-center/webinars/webinar-a-summaryof-testing-rf-power-amplifier-designs-register_255375.html