# Analog Devices Design Tools: ADIsimRF Part 2 This opens the ADIsimRF Calculator window that allows the user to select from many different useful calculators. Last time we took a look at the Vrms, Vpp, dBV, dBm, mW selection and did a short example using a typical ADC usage case. For the sake of time we won’t go through every calculator, but let’s take a look at a few more to get a feel for how helpful this tool can be. First, let’s look at the Decimal to Binary and Hex calculator. This is another handy tool for an ADC guy such as myself. This is a nice tool to convert between the different number formats quickly. In this example I’ve taken the positive full scale value of a fourteen bit converter in two’s complement format which in hexadecimal is 0x1FFF, in binary is 0b01111111111111, or in decimal is 8191. ADIsimRF Calculator Tool – Decimal to Binary and Hex

Another important parameter to consider when dealing with an ADC is the noise spectral density. The NF and NSD in 50 ohms calculator tool will convert between the Noise Figure (NF) and Noise Spectral Density (NSD). It is important to remember though that the tool, being an RF tool, does this calculation in the 50 ohm domain which is the standard impedance in RF applications. When dealing with an ADC, the input impedance is not always set to 50 ohms. In many cases it can be 100 ohms, 200 ohms, or even as much as 400 ohms. If the impedance of the ADC input network is set to a value other than 50 ohms, then the calculator may not be used. However, the ADIsimRF tool can handle this with no problem when doing the signal chain analysis (which we will explore later in this series of blog posts). Please pay attention to the units as well. In RF terms it is more common to look at NSD in dBm/Hz whereas in ADC terms it is more common to look at NSD in dBFS/Hz. As we look at an example in the upcoming blogs you’ll see how easy it is to forget some of these finer details from time to time. ADIsimRF Calculator Tool – NF and NSD in 50 ohms

In any of these calculators only one parameter must be entered to calculate the other parameters. In this example, I simply input the NSD of an ADC in the dBm/Hz box for NSD and the tool (with an assumed 50 ohm system impedance) calculates the noise figure in dB and the noise spectral density in nV/ √ Hz. As an applications engineer I’ve found that different customers like to see different values – some prefer to look at noise figure while others prefer to operate with the noise spectral density in their signal chain analysis. This tool allows the user to operate with their parameter of choice when completing an analysis of a particular application.

When in doubt about the operation of the tool or when looking to find out more information on how calculations are made within the tool, the Help menu can be accessed. This menu has many different items to help the user understand the operation of the ADIsimRF tool as well as some examples. In addition there are some nice generally helpful tidbits of information. 