2018

January 2018

# Understanding Arbitrary Waveform Generator Functional Building Blocks

Posted by BoonCampbell Jan 26, 2018

Quick note: We usually post oscilloscope tips and tricks to this blog, but today we want to share with you about another test & measurement tool often used with or alongside scopes.

In my previous post, I outlined the different types of signal generators in the market today, and what you need to consider when selecting the right fit for your application. I also highlighted why the arbitrary waveform generator (AWG) is my recommendation for you to simulate real world stimulus.

Arbitrary waveform generators (AWGs) are the most versatile signal generators available. An AWG can generate any mathematically-characterized signal, including sine wave, pulse, modulated, multitone, polarized, and rotated signals. The AWG is commonly seen as the workhorse piece of test equipment and can perform the functions of any other generator type. A typical block diagram of an AWG is shown below. The signal flow through the functional blocks starts with a numeric description of a waveform stored in memory. Then the selected waveform samples are sent to a digital-to-analog converter (DAC), filtered, conditioned, amplified and output as an analog waveform.

A common AWG block diagram

## A Closer Look at Each Arbitrary Waveform Generator (AWG) Functional Block

### 1. Memory

A digital representation of a waveform is loaded into AWG memory through a variety of software applications, such as MATLAB, LabView, Visual Studio Plus, IVI, and SCPI. The memory is clocked at the highest sampling rate supported by the AWG. The size of the memory will dictate the amount of signal playback time available. A rule of thumb to determine the playback time is: memory depth divided by sample rate equals playback time. The faster your sample rate, the quicker you will use up the available memory.

### 2. Sequencer

The sequencer circuitry can solve memory depth limitations by arranging (sequencing) the waveform into segments to create your desired waveform. Memory sequencing (or memory ping-pong) does this by only enabling memory during critical waveform portions and then shutting off. You can think about it like this: when recording a round of golf, imagine how much recording time you would save if you only recorded the players striking the ball and not all the walking and setup time. The sequencer does the same thing by only recording waveform transitions and not idle time. Synchronization is maintained by the trigger generator, which enables the waveform. Trigger events can be internal, external, or linked to another AWG.

### 3. Markers and Triggers

Marker outputs are useful for triggering external equipment. Trigger inputs are used to alter sequencer operation, resulting in the desired waveform entering the DAC. Hardware or software triggers can be used for applications requiring exact timing, like wideband chirp signals. They can also be used where multiple AWGs are synchronized together and need to be triggered simultaneously.

### 4. Clock Generator

The timing of the waveform is controlled by an internal or external clock source. The memory controller keeps track of waveform events in memory and then outputs them in the correct order to the DAC. The memory controller saves space by looping on repetitive elements so that the elements are listed only once in the waveform memory. Clocking circuitry controls both the DAC and the sequencer.

### 5. Digital-to-Analog Converter (DAC)

Waveform memory contents are sent to the DAC. Here the digital voltage values are converted into analog voltages. The number of bits within the DAC will impact the AWG’s vertical resolution. The higher the number of bits, the higher the vertical resolution and the more detailed the output waveform will be. DACs can use interpolation to reach an even higher update rate than what was supplied by the waveform memory.

### 6. Low Pass Filter

Because the DAC output is a series of voltage stair steps, it is harmonic-rich and requires filtering for a smooth sinusoidal analog waveform.

### 7. Output Amplifier

After the signal passes through the filter, it will enter an amplifier. The amplifier controls both gain and offset. This gives you the flexibility to adjust output gain and offset depending on your application. For example, you may need high dynamic ranges for radar and satellite solutions or high bandwidth for high-speed and coherent optical solutions.

Use this blog’s functional building blocks to help you understand just what is happening within your AWG and fully utilize the AWG’s capabilities. For a deeper understanding of arbitrary waveform generator fundamentals, I recommend that you download the comprehensive "Fundamentals of Arbitrary Waveform Generation" guide.

## Takeaway and the Demands of Our Connected World

Internet technologies have driven advanced AWG solutions

Our connected world demands increased speed and data complexity. To support this demand, today’s AWGs must:

• Reach higher frequencies while providing wider bandwidth
• Handle complex modulation techniques that cram more data into available bandwidths
• Work with ideal and real-world signals
• Generate signals that stress devices to their limits
• Provide reliable and repeatable results

More on this topic in my posts to come.

# How do I select the right signal generator for my application?

Posted by BoonCampbell Jan 25, 2018

Quick note: We usually post oscilloscope tips and tricks to this blog, but today we want to share with you about another test & measurement tool often used with or alongside scopes.

To develop or test your electronic design, you need to stress it beyond its real-world application. This will insure your device will operate flawlessly for your customers. In some cases, you may find real world stimuli, but most of the time you will need to use instrumentation.

Figure 1. The stimulus test model

The instrumentation needed to develop and test today’s technologies has grown into many signal generator types over the years. The most popular signal generators provided by test and measurement manufacturers are:

• Function Generators
• RF Generators
• Pulse and Pattern Generators
• Arbitrary Waveform Generators (AWG)

There are many generators types out there, so choose yours wisely.

### Function generators

These are the most well-known and cost-effective signal generators. But, they can only provide a limited set of waveforms such as sine, square, and triangle. They are designed to be very easy to use for simple waveforms with limited memory. You can also adjust the generator’s frequency, offset and other output variables as well as the types of modulation.

Function generators are a good general-purpose source. Use function generators when you need a stable and repeatable stimulus signal. You can use them in applications requiring only periodic waveforms such as stimulus response testing, filter characterization and clock source simulation. Some of the more modern function generators are even capable of generating simple AWG waveforms.

### Radio Frequency Signal Generators (RF Signal Generators)

RF signal generators produce continuous wave tones with variable output power levels. RF generator outputs typically range from a few kHz to 6 GHz while microwave signal generators cover from 1 MHz to 20 GHz. Use them to service radio receivers and other RF applications. Keep in mind that there are many types and sub categories of these generators, and Keysight provides solutions from 9 kHz all the way up to 25 GHz.

### Pulse Generators and Pattern Generators

Pulse generators and pattern generators have an advantage over function generators because the output repetition rate and pulse widths can be varied. Their internal circuits may be digital, analog, or a combination of both in order to create the desired outputs. The benefits of direct digital synthesis yield precise frequencies. Use them when working on digital circuits, whereas you should use a function generator primarily for analog circuits.

### Arbitrary Waveform Generators (AWGs)

An arbitrary waveform generator (AWG) can create all the repetitive waveforms that the three generators above can provide. Plus, an AWG can provide single shot pulses and interpolate between defined points. This is helpful when you need to create triangular waveforms. By harnessing the power and versatility of an AWG’s digital signal processing techniques, you can create whatever signals you need to fully exercise your device under test. With this flexibility, you can either confirm proper operation or pinpoint faults within your system. Basically, with your AWG you can create custom solutions for a wide range of applications.

Figure 2. M8195A Keysight AWG

Below is another view of the diverse generator market :-

Signal sourceCharacteristicsWave shape
RF Signal GeneratorsCW (continuous wave) sinusoidal signals over a broad range of frequencies. Modulation types include amplitude, frequency, phase and pulse modulation. May include the ability to sweep the output frequency over a user-set range for frequency response testing.Sine
Modulated sine
Swept sine
Vector Signal GeneratorsDigitally-modulated RF signals that may use any of a large number of digital modulation formats such as QAM, QPSK, FSK, BPSK, and OFDM.Sine
Modulated sine
Pulse GeneratorsPulse waveforms or square waves. Used for testing digital and pulsed systems.Rectangular pulse
Data or Data Pattern GeneratorsMultiple logic signals (i.e. logic 1s and 0s) used as a stimulus source for functional validation and testing of digital circuits and systems.Rectangular pulse
Function GeneratorsSimple repetitive waveforms like sine wave, saw tooth, step (pulse), square, and triangular. May include a modulation function such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM).Sine
Rectangular pulse
Square wave
Triangle
Ramp/saw tooth
Modulated waveforms
Noise
Arbitrary Waveform Generator (AWG)Digitally-based signal source generating any waveform, within published limits of bandwidth, frequency range, accuracy, and output level.All the above

### Use your AWG to simulate real world stimulus

In many scenarios, you need real-world, non-repetitive stimulus to fully test your product. To do this, you need an AWG. In addition, you want to simulate the real-world signals early in the development cycle and fully test the robustness of your designs. An AWG allows you to do this and catch any intermittent or inherent design issues quickly and efficiently. This results in less revisions and gets products to market quicker.

Once the desired waveform is loaded into the AWG’s memory, it can be used to generate an output waveform. You can then adjust your frequency, amplitude, and DC offset and use tools such as triggering, gating, bursts, and modulation to further customize your stimuli. The advanced stimulus created by your AWG allows you to verify product performance limits under worst case conditions. Because of this, the applications for AWGs span virtually all industries.

What kind of signal generator do you need? Function, RF, Pulse or AWG? For real-world, non-repetitive stimuli creation, look to a function or arbitrary waveform generator. To fully utilize your AWG, you should have a basic understanding of the instrument's controls, features, and operating modes. To learn more about AWGs, download the “Fundamentals of Arbitrary Waveform Generation” guide.

# How to Measure Current on an Oscilloscope - Low Current Probing

Posted by ErinEast Jan 25, 2018

As power consumption and energy efficiency become more important, especially with battery-powered devices, it’s necessary to measure extremely low-level signals with higher sensitivity. Lowering your device’s current consumption will, in turn, lower its power consumption.

Power is defined as P = V x I

Having the ability to view the µA range with the highest accuracy possible allows you to analyze the power consumption of your design in detail. This ultimately leads to minimizing the power consumption, therefore maximizing battery life.

One of the main challenges engineers run into is measuring the current consumption of a signal with wide dynamic range. In battery-powered devices, like a cell phone, the device will switch back and forth between active and idle states. During the active state, it will draw higher currents, in the A’s range. But when the device is idle, it draws very small currents, in the µA’s. In Figure 1, you can see the current signal of a cell phone making a phone call. The active peaks have a current of around 2 A, but during the idle states, the current is very small.

Figure 1. Current consumption during a cell phone call

To measure on both of these extremes accurately, a specialized current probe is best. Clamp-on style current probes are typically enough for most measurements, especially if you are only trying to analyze the active periods. However, when measuring on the lower levels during the idle periods, a clamp-on current probe typically has too much noise. The Ohm’s law approach is the best option to measure on the µA or nA level. This means simply measuring the voltage drop across a sense resistor to derive the current. The only sense resistor current probe available with high sensitivity and a wide dynamic range is Keysight’s N2820A current probe, which can be seen in Figure 2

Figure 2. N2820A 2-channel high sensitivity current probe

This is a 2-channel active current probe. Each of the channels has a different gain in order to measure the two different current ranges. When you probe on your device with both channels:

• One channel will give you a zoomed-in view of the µA level
• The other will provide a zoomed-out view of the active, higher levels

The probe also has extremely low noise, which means you will have the highest accuracy possible when measuring on those really low levels. This will help to ensure you are saving even pA’s of current, which may seem small, but can make a huge difference in the system overall.

Figure 3. Zoomed-in view (yellow) of the µA level and zoomed-out view (green) of the larger portions of the current signal in the A range

As I mentioned, this probe simply measures the voltage drop across a sense resistor. You can either cut a line and solder a resistor directly into the circuit, or you can use one of the temporary connectors that come with the probe. The probe comes with a 20 mΩ and a 100 mΩ resistor sensor head ready to use, along with a user-definable resistor head. You can use resistances from 1 mΩ to 1 MΩ.

Selecting the correct sense resistor for your device can be difficult,
but is critical in order to measure different current ranges and characteristics accurately.

If you use a larger resistor, you will get a great signal to noise ratio, which makes for more accurate measurements. The downside to using a larger resistance value is the burden voltage. Burden voltage is the unwanted voltage drop caused by increased power dissipation at the resistor. Using a smaller sense resistor will lower the power dissipation and, in turn, the burden voltage. However, this lower resistor value also comes with downsides, especially with measurement accuracy. Figure 4 below can be used to help determine whether a high or low resistor value would be better for the measurements you are trying to make.

Figure 4. The balance between sense resistor values and measurement specifications

Once you have this wide range of currents accurately captured on the oscilloscope screen, you can learn from it to understand how to adjust your design to increase power efficiency. Area under the curve measurements allow you to understand the charge and easily calculate current consumption over time. You will be able to see where there may be areas where power is being wasted. There could be points where the device should be in its idle state, but some functionality is staying on that is causing for power to be drawn unnecessarily.

Now, you can easily analyze power consumption and see the big picture on the dynamic current waveforms to improve the energy efficiency of your devices. And, built-in automatic measurements make it even easier to take your analysis to the next step and find the root cause of any problems you see.

To learn about which current probe is right for your applications, take a look at the Application Note, How to Select the Right Current Probe.

# Join Wave 2018 for tips, tricks and giveaways to make you an engineering legend!

Posted by KeysightOscilloscopes Jan 16, 2018

Keysight is launching Wave 2018, a first-of-its kind event created to connect you with our experts! Join us March 1-16 to learn helpful tips, discuss the latest ideas, and explore new advances in the industry via daily videos, exclusive content, and live Q&As. Plus, you can register for daily bench and RF giveaways worth up to \$44,000! You won’t want to miss a minute of this event – or your chance to win. You can register now for a free early entry, and mark your calendar for March 1 when we’ll kick off Wave 2018 with a live stream. Get ready to discover an entire Keysight community focused on helping you become an engineering legend!

# Don’t leave it to chance!

Enter Keysight’s Test to Impress contest during Wave 2018 for even more ways to win. Simply submit a short video on why you need test and measurement equipment, and our panel of judges will be awarding one grand prize winner, who will get a bench or RF bundle prize of their choice, and four runner-up winners, who will get a DSOX1102G InfiniiVision 1000 X-Series oscilloscope. Want to see example entries? Check out the 2017 Test to Impress entries playlist.

# What happened to Scope Month?

Wave 2018 is the next evolution of Keysight’s Scope Month, a 2016/2017 month-long oscilloscope-focused event that also featured measurement tips and giveaways. During Wave 2018 you’ll have access to helpful content beyond just oscilloscopes. Learn tips and tricks that will help you master all of the test and measurement tools on your bench. Scope Month had drawings for single oscilloscopes, but during Wave 2018 you could win giveaway bundles that include oscilloscopes, waveform generators, power supplies, digital multimeters, microwave analyzers, and more!

# While you wait for Wave 2018 to begin...

Keysight Bench Facebook Page – Don’t miss out on information about Wave 2018 and other events by following us on social.

Keysight RF Test & Measurement Facebook Page – Keep up with the latest RF/microwave news and content

Keysight Lab’s YouTube Channel – Get a steady stream of how-to videos by subscribing to our YouTube channel.

“EEs Talk Tech” Electrical Engineering Podcast – Join Mike and Daniel as they cover a broad range of topics from the basics of electrical engineering to the tough engineering problems of tomorrow’s technologies.

Keysight Oscilloscopes Blog – Follow for the latest industry news, measurement tips and advice from Keysight oscilloscope experts.

Keysight RF Test Blog – Follow to learn how to improve your RF test measurements.

*The specifics around this event are subject to change. View the latest information at www.wavekeysight.com

# Why Does Apple Slow Down Old iPhones?

Posted by Daniel_Bogdanoff Jan 12, 2018

The internet got all kinds of angry at Apple recently. It turns out, Apple slows down the processor’s clock frequency on older iPhones. The internet took this as an opportunity to jump on “Evil Apple” for what it perceived as a marketing ploy to get people to upgrade.

But, the internet was wrong.

As it turns out, this was simply a case of good engineering by Apple’s engineers.

To understand why they would slow down the processor speed of old phones, you have to understand how lithium ion batteries work and have a basic understanding of processors.

Let’s start by taking a look at lithium ion battery technology.

## Lithium Ion Battery Technology

Mobile devices use lithium ion batteries primarily because of their incredible energy density. They provide a lot of power and don’t take up much space.

We all want a battery that lasts a week. That is, until we have to carry it. Engineers must find a sweet spot somewhere between device usability and eternal battery life (known as “battery heaven”).

To understand Apple’s problem, you need to understand how lithium ion batteries (LIB) work. LIBs use a chemical reaction in which the anode (lithium-doped cobalt oxide) passes lithium ions to the cathode (graphite) through a special barrier. The ions, using an electrolyte as a conductor, can pass through this barrier. Electrons cannot, and therefore get provided to the circuit. Note the electrons in the half-reactions for the cathode and anode:

Figure 1.  Cathode half-reaction

Figure 2. Anode half-reaction

If there’s a path for the electrons, the chemical reaction will take place. If there’s not, the battery hangs in a balanced state and holds its charge.

But there’s a catch. LIBs age. A test from Battery University showed that LIBs experience a capacity drop of up to 20% after 250 charge cycles.

Not only do LIBs lose capacity, but they also lose the ability to generate high levels of current. The current production capability of an LIB is proportional to how fast its chemical reaction takes place. The faster the reaction, the higher the current.

When choosing a battery for your product, one spec you should consider is the current production capability. Typically, you know your required currents, so this is an easy call. Choose a battery that will give you enough current to power your design and enough extra headroom to be comfortable. But what happens a few years down the road? Your battery’s performance will degrade, but your device will still need the same amount of power.

The environment also takes a toll on LIBs. Like any proper chemical reaction, temperature is a factor. The colder an LIB, the slower the chemical reaction, the lower the peak current. Couple this with an old, degraded battery and you’re in for some trouble.

Eventually, you’re going to run out of extra power-generation capability. This is the problem Apple’s facing. Their older-model iPhones still require the same power that they did on day one, but their batteries aren’t holding up.

Now, Apple is slowing down your phone! Why? It’s actually for your own good. The reasoning comes down to how processors work.

## Processors Need Power

Basically, processors are just an intelligently organized collection of transistors. When combined, they make up logic gates that form the core of modern processing (no pun intended). For gates to function properly, they need power. If a gate doesn’t get enough power, it’ll still work; it’ll just operate more slowly.

Figure 3.  Low supply voltages mean increased propagation delay!

Heavy processing tasks require a lot of power, and mobile devices are designed to handle this load. But what happens if a device’s battery is degraded to the point that it can’t provide enough power?

Without sufficient power to the processor, the gates won’t operate as fast. Put simply, their propagation delay increases. Processors operate expecting a certain propagation delay. The timing of its operations depend on logic blocks making decisions within an expected number of clock cycles. Low power to a processor slows down logic blocks.

Then things break.

Then what? If you have a well-designed device, it’ll realize there’s an issue and simply perform an emergency shutdown. If your device isn’t so well designed, the electronics can be damaged.

Don’t take it from me, Apple says as much in their statement on this matter:

"Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices. Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components.

Last year we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions. We've now extended that feature to iPhone 7 with iOS 11.2, and plan to add support for other products in the future."

So, what are Apple engineers actually doing to “prolong the life of their devices?” They’re slowing down the CPU frequency if the phone detects an insufficient battery voltage.

An iPhone owner on Twitter documented their iPhone 6’s CPU jumping from 600 MHz up to 1400 MHz after a battery replacement.

## How iPhones Deal with Old Batteries

Apple is attacking this issue on two fronts.

The first is clear from the Twitter example – a slow down of the phone’s CPU frequency. The old battery’s lower power capability means a larger propagation delay in the processor. Slowing the CPU frequency ensures that there’s enough buffer time to cover a non-ideal propagation delay.

The second is addressed in Apple’s statement. Apple’s engineers are spreading out processor-heavy clock cycles to minimize the required battery power.

## What Can You Do About It?

How do you avoid experiencing phone slow down?

First, take care of your battery. Don’t let it get too hot, especially if it’s fully charged. Also, don’t use off-brand chargers. A lower charging voltage is proven to prolong battery life, but it also takes longer to charge.

Second, expect to get a new battery every 350-500 charge cycles. They are not that expensive compared to a new device, and they can massively improve processing performance.

If you’re designing devices that use LIB, your users’ experience can hinge on battery management.

Make sure to have proper air flow around the battery. Also, think about whether or not the battery should be user-serviceable. Plan for battery degradation when selecting a battery and designing battery management circuitry.

Figure 4.  Design with battery limitations in mind!

## It Seems Apple Isn’t Evil

Though some people may wish it were true, this wasn’t an evil corporate marketing scheme. It’s just good engineering. A closer look at processor basics and lithium ion battery technology shows that Apple is simply doing what they have to do to improve their users’ uptime – a noble goal.

I’d love to hear your thoughts on the issue. Let me know on Twitter(@Keysight_Daniel), the Keysight Bench Facebook page, or the Keysight Labs YouTube channel!

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