Skip navigation
All Places > Keysight Blogs > EEsof EDA > Blog > 2016 > August
2016

Jack Sifri, MMIC/Module design flow specialist, outlines 4 steps on how to effectively tune the performance on your RF board design in this latest article from High Frequency Electronics.

Step 1. Create a Top-Level Schematic. 

Step 2. Use the EM Cosimulation (emCosim) method. 

Step 3. Launch ADS Momentum and perform the EM simulation.

Step 4. Plot the results in data display.

 

Read more about these 4 steps and how he applies them to a real-world example by clicking on the link to the article.

 

It is often the case that our manually calculated values do not provide optimum performance. Tuning is a way to change the component values and see the impact on circuit performance. Optimization is an automated procedure of achieving the circuit performance in which ADS can modify the circuit component values in order to meet the specific optimization goals. Download the Tuning and Optimization chapter from the ADS Example Book.

 

Click HERE to download more chapters.

In a previous blog I described the benefits and challenges to the implementation of co-design. To better understand the concept of co-design, let us consider the design of an RF receiver with acceptable performance that will not render the algorithms ineffective, and in particular, a side-looking Synthetic Aperture Radar (SAR) on an airplane that covers an area on the ground (Figure 1). blog 2 figure 1.png

Figure 1. Airplane mounted SAR.

 

As the plane flies, its antenna beam sweeps the area. Linear frequency modulated radar pulses are continuously transmitted and return pulses are collected. From the returned pulses, an image is reconstructed. This reconstruction is enabled by signal processing algorithms. The returned signals are at microwave frequencies and, therefore, have to be properly down converted to the baseband before processing them. The RF receiver must perform this task without significantly degrading the signal quality.

 

Rather than having radar transmit completely in baseband, an algorithm is used to take a picture, take the raster scan of pixels, analyze at the luminosity, and put the scans out as a data stream. The reflections of signals coming back into the radar front-end are then processed. Next, the long stream is taken, chopped into pieces and put into a picture.

blog 2 figure 2.pngFigure 2. From left to right, the impact of an increase in phase noise in the oscillator is shown. The amplifier is close to
compression in the right image.

 

While evaluating the quality of the images produced, the RF amplifier, RF mixer, down converting Local Oscillator (LO), amplifier nonlinearity, LO phase noise, and mixer characteristics are all considered. In this case, the LO phase noise caused the RF receiver’s contrast to suffer slightly (Figure 2). Although difficult to pick up with the eye, the impact can be seen in numeric measurements.

 

On the other hand, a significant visible impact can be seen with the amplifier going into 1-dB compression. As it gets close to its compression point, a great deal of detail and sensitivity is lost and washed out.

blog 2 figure 3.png

Figure 3. The change in image quality as A to D is changed from 14 to 6 bits can be observed from left to right.

 

Loss of detail comes from other sources as well. For example, let’s examine an Analog to Digital Converter (ADC). When it is moved from IEEE double-precision floating point to 14 bit to 12 bit and then to 10 bit, banding starts and there is a loss of detail (Figure 3). By the time six bits is reached, significant amounts of detail in the images are lost. At 6 bits,
an Automatic Gain Control (AGC) may need to be added on the front end. Auto scaling can be performed to get it into the sweet spot of the ADC.

 

In conclusion, in SAR, there are many contributing factors that can cause loss of detail and image quality. In order to compensate for this, co-design of DSP and RF can be used to produce better results.

 

Want to learn more about this example? Check out Dr. Murthy Upmaka's IMS 2016 MicroApps presentation.

 

In all areas of business, increased communication leads to more streamlined processes and greater potential for success. This is no less true in system design. Within large design organizations, baseband Field Programmable Gate Array (FPGA) and Radio Frequency (RF) signal processing communities have traditionally been separated. Today, however, many RF functions are moving into the algorithmic world and this is making communication between the two areas more crucial than ever. Blog 1 imge.png

 

Co-design, a process whereby all stakeholders actively participate in the design process, offers a solution to this dilemma. While organizations have certainly successfully designed electronic systems like wireless communication systems, smart phones and space systems without co-design, its’ use offers not only the potential for reduced risk and cost, but accelerated time-to-market as well; enviable advantages for any modern design organization. It’s not surprising then, that the co-design of baseband algorithms and RF distributed circuits has emerged as a critical and important trend. For modern design organizations, it’s now more imperative than ever that they simulate both Digital Signal Processer (DSP) and RF circuits together at the system level using mixed signals.

Blog 1 image.png

Co-Design Benefits

Without a doubt, co-design offers designers a number of important benefits. For example, by co-designing DSP and RF circuits, over design, inaccurate predictions and difficulties in assembly can be prevented. In contrast, organizations that utilize disparate design flows with little to no communication and don’t co-validate along the way can anticipate added cost and complications. The algorithmic engineers have a hard time accounting for RF signal impairments in the signal processing, while those working on RF circuits aren’t able to clearly see how their systems are being used in the overall
infrastructure. Co-validation during the design process allows for some of these problems to be accurately accounted for, and lets organizations find the cheapest technique to solve a problem.

 

Co-Design Challenges

Despite these benefits, DSP and RF co-design is not without its challenges. DSP and RF circuits are simulated with different techniques. DSP is typically done in the numeric and time domain whereas RF circuits are designed using frequency-domain techniques. Converting between the two domains takes a long time and even when RF is changed into the time domain, many elements still exist in the frequency domain. You either have a very detailed RF model that is trusted completely, but need to simplify the signals, or arbitrary signals on the baseband side with an extremely simplified RF. Co-design bridges the gap, offering the right level of behavioral modeling on both sides.

 

Interested in learning more about DSP and RF co-design? Watch this 13- minute video on YouTube -  Dr. Murthy Upmaka's talk at IMS 2016.