Sunday, February 27, 2011

Low Cost Solution for Measuring Frequency Hopping

Frequency hopping is a method of switching or "hopping" a carrier signal among many frequency channels, using a pseudo-random sequence known to both transmitter and receiver. Frequency hopping is more widely known in wireless communication, but it is also used in radar where it is sometimes referred to as an agile signal or agile carrier. In wireless communication frequency hopping is a way to lower signal interference and share a small section of bandwidth. It also serves as a method to protect a signal against ease-droppers. In radar frequency hopping is used to guard against jamming and deception or as a way to reduce signal interference. 
To measure the frequency and modulation content on a comm or radar signal the signal analyzer or similiar instrument is typically the solution of choice. But lets say you wanted to measure or capture a long record of frequency hop data to check long term accuracy or validate an algorithm or verify frequency channel transitions, how would you do it? You could use a high speed digitizer or mixer digitizer combo with a lot of memory. You then would have to post process the digitized data to create an easy to read frequency plot. 
An easier low cost way to do it is with a modern universal counter that has gap-free measurement capabilities. A counter works by making high accuracy and high resolution timing measurements between signal edge events. A counter with gap-free measurement capability can make timing measurements without any rests or gaps in between up to a certain sample rate. For instance the Agilent 53230A counter has a gap-free sample rate of 1 MS/s. What that means is if you have a carrier at 2.4 GHz the 53230A will pre-scale or divide down the signal to fit the sampling rate. You can than use the pre-scale value and the resulting timing measurement to calculate frequency on a continuous bases. Since a counter is just making edge event timing measurements and not digitizing you can make a lot of high resolution frequency measurements without using much memory at all.
As an example, below are two plots of 32,000 frequency measurements made on a frequency hopping carrier signal using the 53230A. The plot has frequency on the Y axis and time on the X axis (click on the figure to enlarge).

The frequency range of the signal is about 2.48 to 2.58 GHz. The top view shows all of the measurements and the bottom plot is a zoomed in picture of about 850 measurement points at one of the carrier hop levels. The bottom plot shows that even though we are capturing a large time slice of frequency hop measurements we still have ample measurement resolution to zoom in and see noise on the carrier. 
The 32,000 measurements made at a 1 MS/s rate only took up about 3% of the 53230A's 1 million measurement reading memory. Imagine the price tag on a digitizing based solution that could capture that much high resolution frequency data! Besides just capturing long periods of frequency hopping data the gap-free measurement capability found in modern universal counters also can be used as a low cost modulation domain analysis and close-in noise analysis tool on carrier signals.

Monday, February 21, 2011

Simulating Complex ECG Patterns with an Arbitrary Waveform Generator

Using an electrocardiogram (ECG sometimes called an EKG) is an invaluable way to identify various physical ailments. Today there is a wide array of cardiac equipment that displays and interprets ECG signal patterns. Medical equipment designers need a flexible way to seamlessly generate accurate ECG signal patterns to verify and test their designs. In this post, I will discuss how to generate complex ECG signal patterns with an arbitrary waveform generator (AWG). Below in the figure is a 12-lead ECG waveform.

There are three methods to create and store an ECG on an AWG:
1. You can use a device such as a digitizer or oscilloscope to capture an actual ECG signal from a patient. Then you upload the digitized points to the AWG. With modern AWGs, there are many ways to accomplish this, including using a .csv file and a memory stick.
2. You can use mathematical software to create an ECG signal. There may be custom software for the AWG that can do this, or you could use a standard software package, such as MATLAB ®.
3. If your instrument has this capability, you can use your AWG’s built-in "typical" ECG waveform. The Agilent 33521A has a built-in ECG waveform.

Using an AWG’s arb sequencing capability to simulate complex ECG patterns
AWGs that have arb sequencing ability, like the 33521A function/arb waveform generator, can seamlessly transition from one arb waveform stored in memory to another without any discontinuities in the output. The figure below shows an example using the 33521A’s arb sequencing feature to combine three different ECG waveforms stored in different places in memory into one waveform.

The first ECG waveform cycle is meant to be an "ideal" ECG waveform. The other two were based on the first one but were changed in a systematic way using MATLAB software. Notice the second ECG
waveform has a flattened T wave. In the third ECG waveform, the T wave is inverted.
The 33521A’s sequencing capability provides flexibility for controlling when it sequences from one waveform to another. One way to control sequencing is to specify how many cycles each waveform is run before sequencing to the next. Sequences can also return to a waveform that was used previously in that sequence.
Combining the 33521A’s arb sequencing feature with its large arb memory, 1 million points per channel standard with 16 million optional, gives you the ability to simulate complex ECG patterns for thorough testing of cardiac monitoring equipment designs. For example, each ECG waveform shown in the above figure were created with about 500 points. You could store up to 2,000 different ECG waveforms of this size in the 33521A’s standard arb memory. The 33521A allows arb sequences to contain up to 512 steps, allowing you to create complex ECG patterns for thorough testing. You can control arb sequences on the 33521A asynchronously by using triggers to control waveform transitions instead of cycle counts. This provides you with the ability to continuously cycle a waveform for some undetermined time period until it receives a software trigger or external trigger or front-panel trigger. Once it receives the trigger, the 33521A transitions to the next waveform in the sequence. You can also mix the two ways of transitioning through a sequence, specifying a count and using triggers.

Free Matlab ECG simulation program
You can download and use an ECG simulator program created in MATLAB®. You can find the ECG simulator download and instructions at simulation-using-matlab or type “ECG MATLAB” into a search engine and it should be at the top of the results. The program creates ECG waveforms using multiple Fourier series summed together. A Fourier series is used for each distinct wave shape in the ECG waveform, such as the P wave, T wave, etc. The program allows you to adjust various ECG waveform parameters to simulate various cardiac conditions. You can then transfer the ECG waveform you created to a 33521A either by storing it in a .csv file and using a memory stick or remotely via Matlab's instrument toolbox feature.

Tuesday, February 15, 2011

Agilent Redefines Oscilloscopes with the new InfiniiVision 3000 and 2000 X-Series

On 2/15/2011 Agilent released its new scope family, the InfiniiVision 3000 and 2000 X-Series. After reading the title of this post the first question that probably popped in your head is: "what about this new scope family is so redefining?" The three main headlines for this new family of scopes that really makes it redefining are it gives you a lot of scope at a great price, it has the capability of 4 instruments in 1, and its upgradability. A lot of scope at a low price means the InfiniiVision X-Series delivers:
  • Largest display in class with a 8.5-inch WVGA display
  • Fastest waveform update rate in class at 1 million waveforms per second
  • Deepest memory in class 4 Mpts with MegaZoom IV technology
  • Offers 33 automated measurements, nine parametric triggers, six serial protocol triggers, as well as seven waveform math functions including FFT
The 4 instruments in 1 includes:
  1. Best in class scope
  2. Logic timing analyzer
  3. Protocol analyzer (optional)
  4. WaveGen built-in function generator (optional)
You heard me right this family of scopes offers an optional function generator. This is an industry exclusive feature! It is a 20 MHz function generator that can do sine, square, ramp, pulse, DC, and noise waveforms. The optional function generator capability is ideal for educational or design labs where bench space and budget are at a premium.
Finally easy upgradability to protect your investment. Project needs change, but traditional oscilloscopes are fixed - you get what you pay for at the time of purchase. With the InfiniiVision X-Series if you need more bandwidth (up to 500 MHz), digital channels, WaveGen, or measurement applications in the future, you can easily add them all after the fact. 
To get more info on Agilent's new InfiniiVision 3000 and 2000 X-Series Oscilloscopes check out the links below:

Tuesday, February 8, 2011

Scope's Segmented Memory Feature Makes Skipping Points a Good Thing

If you work with signals that have relatively long idle times between low-duty-cycle pulses or bursts of signal activity, then you'll love the segmented memory feature available in today's scopes. Segmented memory allows you to capture more selective signal details with less memory. With segmented memory, the scope’s acquisition memory is divided into multiple smaller memory segments. This enables your scope to capture a whole bunch of successive single-shot waveforms with a very fast re-arm time — without missing any important signal information.  In simpler terms it is a way for you to optimize your scope memory usage by only capturing the signal segments you are interested in. The second advantage segmented memory provides is a user interface that allows you to easily view the signal segments to check overall signal quality or to quickly find that needle in a hay stack bug that you know is out there. After a segmented memory acquisition is performed, you can easily view all captured waveforms overlaid in an infinite-persistence display and quickly scroll through each individual waveform segment. Common applications for this type of oscilloscope acquisition include high-energy physics measurements, laser pulse measurements, radar burst measurements, and packetized serial bus measurements. Below is an example of using segmented memory in a high-energy physics application.

High-energy physics and laser pulse applications 
Segmented memory acquisition in an oscilloscope is commonly used for capturing electrical pulses generated by high-energy physics (HEP) experiments, such as capturing and analyzing laser pulses. With segmented memory acquisition, the scope is able to capture every consecutive laser pulse, even if the pulses are widely separated. the figure below shows the capture of 300 successive laser pulses with a pulse separation time of approximately 12 ┬Ás and an approximate pulse width of 3.3 ns. All 300 captured pulses are displayed in the infinite-persistence gray color, while the current selected segment is shown in the channel’s assigned color (yellow for channel 1).

Note that the 300th captured pulse occurred exactly 3.62352380 ms after the first captured pulse, as indicated by the segment time-tag shown in the lower left-hand region of the scope’s display. With the scope sampling at 4 GSa/s, capturing this amount of time would require more than 14 Megapoints of conventional acquisition memory. If these laser pulses were separated by 12 ms, the amount of conventional acquisition memory to capture nearly 4 seconds of continuous acquisition time would be more than 14 Gigapoints. Unfortunately, there are no oscilloscopes on the market today that have this much acquisition memory. But since segmented memory only captures a small and selective segment of time around each pulse while shutting down the scope’s digitizers during signal idle time, scopes can easily capture this much information using just 8 Megapoints of memory

Agilent’s InfiniiVision Series oscilloscopes are the only scopes in the industry that not only provide segmented memory acquisitions simultaneously on all analog channels (up to four analog channels) and logic channels (up to 16 digital channels) of acquisition, but they also are the only scopes that provide hardware based serial decoding on packetized serial data for each captured waveform segment. The InfiniiVision Series includes the scope I have on my bench, the MSO7054A (although now they are on the B model so looks like I need to upgrade).

Click here for more on Agilent's segmented memory feature

Click here for more info on the scope I have on my bench (the B model though)

Thursday, February 3, 2011

N6781A SMU was Named One of EDN's HOT 100 Products for 2010

Agilent's N6781A SMU for battery-drain analysis was one of EDN's HOT 100 products for 2010! Congrats to the N6781A R&D team for their innovative hard work.

The N6781A has an Agilent only patented seamless ranging technology that allows its 18-bit current measurement digitizer to switch from one measurement range to another with no discontinuities in the output. I actually briefly mention the N6781A in my last blog post and I cover its features and capabilities in detail in my June 27th 2010 post. The seamless ranging capability is key for handheld device design where power optimization is critical because it allows you to fully characterize the device's dynamic current profile as it transitions through various standby and operation modes. The N6781A can simulate the device's battery or it can serve as a zero ohm shunt for battery rundown tests. The N6782A is the sister product to the N6781A and it also has seamless ranging capabilities. The N6782A is geared more towards low power optimization at the component and circuit level.

Full list of EDN's HOT 100 Products click here

N6781A product page

EDN article on the N6781A click here