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2018

As you walk through your lab, take a look at each RF bench. How old are your signal and network analyzers? How often are they kludged together to create one-off measurements? How recently have your engineers bugged you about getting new equipment that can actually test your latest RFIC?

 

I’m here to help you make a stronger case when your team’s success depends on timely access to better RF instruments. This post introduces language, concepts and solutions that will help you influence purchase decisions and improve your chances of getting the right tools at the right time. When you apply these ideas, your newfound business sense may surprise—if not impress—your boss or boss-squared.

 

Understanding your current reality

Day to day, you deal with competing objectives: delivering excellent results while staying within stringent constraints. From a high-level business perspective, there are three ways to do this: cut costs and deliver the same topline; hold costs steady and increase revenues; or invest more to create a giant leap in output. These days, most organizations operate within the first two scenarios while fast-growing companies chase the third.

 

Getting the right tools at the right time (and place)

Whichever situation you face, one of your biggest issues is likely to be test equipment. In fluent “manager speak,” “test assets” are often your organization’s most “underutilized assets.” Why? Because it’s difficult to confidently determine two crucial bits of information: the location of every instrument and how much each one is truly being utilized.

 

For you and your team, easy access to the right tools enables everyone to do their best work and stay on schedule. Applying manager-speak once more: for “technical staff,” “highly available” test equipment can be a “high-leverage asset.”

 

Pushing for better decisions in less time

An accurate view of location and utilization is essential to making credible decisions in less time: Do you need to purchase or rent additional equipment? Is it better to redeploy, upgrade, trade in or sell some of your existing gear?

 

A few basic changes can provide three big benefits: better visibility, improved utilization, and reduced expenses (capital and operating). The starting point is a solution that puts real-time information at your fingertips. Relevant information about test-asset location and utilization is essential to greater availability and improved productivity.

 

Taking the next steps

Being able to make quick, thoughtful decisions on how to best equip your engineers with the right tools is the foundation for a successful organization. To learn more, check out our latest resources to better understand how to drive down your total cost of ownership.

 

Please chime in with any and all comments. How difficult has it been to get the test tools your team needs? What techniques have you used to help make it happen?

Prove yourself as an engineer! The Schematic Challenge is the perfect opportunity to test your skills. On March 12, 13, and 14, we will be posting a new schematic or problem-solving challenge. If you, as a community, are able to answer questions 4, 5, and 6 correctly by Thursday, March 15 at 11:59 PM MST, we will add three 1000 X-Series oscilloscopes to the overall Wave 2018 giveaway! Answers should be posted in a comment on the #SchematicChallenge posts on the Keysight Bench or RF Facebook pages. Work with your family, friends, coworkers, or fellow engineers in the Wave community to solve these problems. If you haven’t already, be sure to register for Wave 2018 at wave.keysight.com.


Question 4:

By Ryan Carlino

 

Status: SOLVED! (A=1 and B=2)

 

Week2 Q4 Schematic Challenge Wave2018

Given this circuit and assuming an ideal op-amp powered by +/-5V and ideal resistors, calculate the output voltage with respect to the input. Vin will be limited to +/-1V.

Express this transfer function like this:
Vout = A*Vin + B

The answer being posted should be a single number AB. For example, if A=4 and B=7, the answer you should post is 47.

 

Question 5:

By Jonathan Falco and Lukas Mead

 

Status: SOLVED! (90 MHz)

 

What integer frequency in MHz should the LO be set, to allow the RF input range to be seen on OUT?

 

.


Question 6:

By Barrett Poe

 

Status: SOLVED! (4-10-8-8)

 

You are asked to design the front end of a 10 MHz oscilloscope. The “front end” refers to the internals of an oscilloscope between the probe and the analog to digital converter. Your system requires you take a +/- 10V signal input, and output a 0-3.3V signal to the ADC input, which is terminated at 50 Ohms. Your circuit must scale, offset, and filter the incoming signal, then rescale it to the full range (within 10%) of the ADC’s reference voltage without clipping the sampled signal.

 

Oh no! You also just discovered your supplier has discontinued your favorite ideal operational amplifier (opamp). Your next two best choices are:

  • Opamp with 1 pF of capacitance on the inputs
  • Opamp with 10 pF of capacitance on the inputs

Make sure your design works with both of these back-up options. However, note that you will only use the same parts together. Meaning, you will only ever have two 1 pF opamps OR two 10 pF opamps, never one of each.


Also keep in mind – opamp output voltage cannot exceed the supply rails.

Output Voltage = 0 to 3.3V; Ensure Vout is +0%/-10% of ADC range for max input across bandwidth

Frequency = DC to 10 MHz

 

Assign a value to variables a, b, c, and d. The final answer to be posted on Facebook should be expressed as: a-b-c-d. For example, if a = 8, b = 6, c = 12, and d = 10, then the answer should be expressed as: 8-6-12-10.

 

HINTS:

The variable “a” is equal to one of these three options

  • c-1
  • 4
  • 4b

The variable “b” is equal to one of these three options

  • c+1
  • 4
  • 10

The variable “c” is equal to one of these three options

  • b/2
  • 6
  • 2*a

The variable “d” is equal to one of these three options

  • 8
  • (b+2)/3
  • 10

Helping You Achieve Greater Performance and Fast Measurement Speed

At an exhibition demo booth, an engineer complained to me about the measurement speed of a PXI oscilloscope. To make a measurement, he programmed the data acquisition and post-analysis himself. The test took him over a minute to get each result. I told him that he didn’t have to do all of that; all he needed to do was setup the measurement on the oscilloscope and fetch the measurement item result directly. The process should only take a couple of microseconds. An on-board ASIC helps minimize data transfer volumes and speed-up analysis!

 

Like an oscilloscope has on-board digital signal processing, RF signal analysis tools also have on-board processing to accelerate measurement speed.

 

RF Measurement Challenges

For RF signal analysis, it's common to frequency-shift the RF signal to an intermediate frequency (IF) so that you can use a high-resolution digitizer for a high dynamic range signal acquisition. This then gets sent to a PC for data analysis. However, the complexity of this analysis increases with today's wireless communication systems, such as 5G technologies, 802.11ax standard and so on. Measuring these systems can include complex modulation schemes (e.g., orthogonal frequency-division multiplexing, OFDM), carrier aggregation, or MIMO (multi-input multi-output) signals.

 

These complications require significant signal processing, which in turn slows the measurement speed. This is a challenge as measurement throughput is critical in most applications, especially in high volume production testing.

In most signal analyzers, a digitizer is an indispensable component. For wider bandwidth analysis, you need a high-speed digitizer to capture signals. At the heart of a high-speed digitizer is a powerful FPGA or ASIC that processes data in real-time. This allows data reduction and storage to be carried out at the digital level, minimizing data transfer volumes and speeding-up analysis.

 

A key feature often available on digitizers is real-time digital down conversion (DDC). In frequency domain applications, DDC allows engineers to focus on a specific part of the signal using a higher resolution, and transfer only the data of interest to the controller/PC. It works directly on ADC data providing frequency translation and decimation sometimes called "tune" and "zoom." The block diagram shown in Figure 1 illustrates this basic concept of DDC.

 

Digital down-converter block diagram

Figure 1. Digital down-converter block diagram

 

How DDC Works

The frequency translation (tune) stage of the DDC generates complex samples by multiplying the digitized stream of samples from the ADC with a digitized cosine (in-phase channel) and a digitized sine (quadrature channel).

The in-phase and quadrature signals can then be filtered to remove unwanted frequency components. Then, you can zoom in on the signal of interest and reduce the sampling rate (decimation).

 

Finally, the on-board processor sends only the data you care about (I/Q data) to the on-board memory for further analysis. Most of Keysight's digitizers and signal analyzers have implemented DDC to accelerate measurement speed and for demodulation acceleration.

 

In addition, you can perform FFT with I/Q data in parallel for spectral analysis.  Some signal analyzers can do real-time FFT processing (nearly 300,000 times/second) and use comprehensive spectrum displays (density and spectrum) so that you won't lose any agile signals on the screen, shown in Figure 2.

 

Real-time spectrum analysis at 2.4 GHz ISM bandFigure 2. Real-time spectrum analysis at 2.4 GHz ISM (industrial, scientific and medical) band

 

Benefits and Limitations of a High-Speed Digitizer with DDC

Using a high-speed digitizer with DDC for your RF testing can be significantly more efficient:

  1. The frequency translation (tune) reduces both on-board memory and data transfer requirements. The resulting data is in complex form (I+jQ), which is usable for demodulation analysis directly and accelerates measurement speed.
  2. Digital filtering and decimation (zoom) reduce the wideband integrated noise and improve overall SNR.

 

However, there are some limitations with DDC implementation:

  1. The ADC's sampling rate is limited. It's not possible to digitize the high-frequency carrier directly. A common workaround is to use an analog circuit to bring the carrier to an IF so the digitizer can acquire the signal.
  2. The ADC's dynamic range is also limited. In wireless communication systems, you may need to capture both large and small signals at the same time.

 

New generations of high-speed and high-resolution ADC technologies provide excellent resolution and dynamic range into the tens of GHz, which allows you to capture high-resolution wideband waveforms. DDC accelerates measurement speed and increases processing gain to improve performance.

 

Furthermore, the I/Q data can be processed further for advanced real-time signal analysis or sent to a customized FPGA for user-defined signal processing algorithms. These provide you better RF measurement fidelity, signal integrity and higher measurement throughput.

 

If you’d like to learn more about wideband signal acquisitions, you can refer to the following white paper Understanding the Differences Between Oscilloscopes and Digitizers for Wideband Signal Acquisitions to understand what you should be using for your application.