I hope that my recent series of blog posts on IMS2015 in Phoenix was insightful as well as interesting. I really enjoy attending the show and letting folks out there know about the experience. I just read over some show statistics today and it looks like there were over 4,000 attendees; that is quite an impressive number! I hope that by reading about the IMS show through this blog that it encourages more folks to attend and see what all the papers, presentations, exhibits, and events have to offer. It is not only an educational experience but also an entertaining one. Often as engineers we do not let loose very often and have fun. Attending the show accommodates both the necessary learning while offering time to enjoy some fun events. Before the IMS show I was in the middle of a series of blogs on the design tools that Analog Devices offers. Let’s now continue that discussion looking at the ADIsimRF tool.
The topic of this blog came up while at the IMS show and one of my colleagues mentioned that I should discuss the ADIsimRF tool as a part of the series. I thought this was a marvelous idea. I’ll have to precursor this discussion with the fact that I am actually an RF guy from my previous employment at an RF company which was my first position when I graduated from college. I had a great learning experience at that position being around many who were very knowledgeable RF engineers. These folks taught me many things about RF as well as the professional life. Through some interesting events (which may be a topic for some future blog) I ended up getting an incredible opportunity to work with high speed ADCs at Analog Devices where I am currently.
All that being said, you can get a small peek at why my ears perked up a bit and my curiosity peaked with my colleague’s suggestion to do a blog on the ADIsimRF tool. It has not been often over the last four to five years that I have had an opportunity to work with RF frequencies. Much of the work I’ve done with high speed ADCs has been at 400 MHz or lower with most applications being around 200 MHz. As I’ve heard often “One man’s RF is another man’s IF.” Basically what may seem like a high frequency to one may be a low frequency to another. Personally, based on my experience, I generally consider RF to be 400MHz and higher. This is due in part to the fact that at my first position working with RF I did not work with anything below 400 – 450 MHz. That has been further justified in my current work with high speed ADCs where much of my work has been below 400 MHz which many do not consider as RF. The frequencies I work with are changing however as high speed converters move into the GSPS space where the input frequencies are moving to as high as 2 GHz.
Now that we have had a short history lesson as well as a short IF/RF debate, let’s take a closer look at the ADIsimRF tool. The software is available for free from the Analog Devices website and can be downloaded after filling out a short software request form here: ADIsimRF and appears as such:
The ADIsimRF allows for a signal chain to be analyzed before prototyping the circuit in actual hardware on a lab bench. By default the software loads up with ten stages. The number of stages may be set to between 1 and 20. There are a number of devices available including baluns, amplifiers, filters, ADCs, and DACs. The individual stages have input selections to determine various parameters for the different devices (i.e. gain, input/output impedance, etc.). There is also a section for the input signal statistics at the bottom of the GUI. To the right of the input signal statistics box there is an analysis window that give the results of the simulation. Parameters such as Power Gain, Noise Figure, Output NSD, SNR, OIP3, etc. are reported. The tool can be set up to analyze Transmit or Receive applications. The default is set to Transmit. Being an ADC applications engineer, I mostly work with the Receive features of the ADIsimRF tool. Before we dive into a full example I’d like to spend some time looking at a couple of nice features of the tool. First let’s look at the included calculator tool.
The calculator tool has several settings that enable the user to do conversions between different parameters and units. By default the setting selections Vrms, Vpp, dBV, dBm, mW which is especially useful for a high speed ADC guy like myself. Let’s look at an example. It is often quite useful to determine what input power will result in a -1 dBFS input signal for an ADC. For the case of an input resistance of 200 Ω and a 1.75 VPP full scale ADC voltage, the tool shows us that an input signal of 2.8 dBm would be required to achieve -1 dBFS. Generally in the lab when working with an ADC these are the most important parameters. I am using a signal generator that displays the output power in dBm and am using an ADC where I have set the full scale voltage and I know the input impedance. The calculator tool also returns RMS voltage, volts in dBV, power in mW, and other parameters.
This is a useful place to start as it gets our input conditions set for our signal chain. Next time, we will continue looking at the ADIsimRF tool and its capabilities. As we will see it is actually a nice bridge between the RF domain and the world of high speed ADCs (at least that is one perspective of the tool and one which I am partial to since I am a high speed ADC guy!). There are many potential uses of the tool and I hope you will enjoy the journey as we explore ADIsimRF over the next few blogs.