Stability and Gain Circles University of San Diego（稳定和获得圆大学圣地亚哥）.pdfVIP

ADS Tutorial Stability and Gain Circles EEE 194RF The first step in designing the amplifier with the S parameter method is to determine whether the amplifier is unconditionally stable or potentially unstable. This can be easily estimated using the K stability factor and delta. The amplifier will be unconditionally stable if: K 1 and mag() 1. These factors are easily calculated using Measurement Equations in the ADS schematic panel. K is pre-programmed in as stab_fact which can be selected from the S-parameter palette on the left. Delta can be programmed yourself using a blank MeasEqn. The maximum available gain (MAG) and maximum stable gain (MSG) can also be calculated using the max_gain function. When swept over a range of frequencies, it can be clearly seen where the device will be unconditionally stable (above 1.5 GHz for this example). Note that the user-defined equation capability of the display panel is used to also calculate and plot MSG and the intrinsic transducer gain (GTi) with both and = 0. In the regions where K 1, the S L max_gain function plots MSG. When unconditionally stable, it plots MAG. ADS tip: When you want to plot from your user-defined equations, you need to select the equations dataset in the plotting panel. Equations MSG MAG Unstable Next, you could check (as the book suggests) to see if the device is unilateral. (this is rarely the case). Evaluate the Unilateral Figure of Merit, U, at the design frequency using a Measurement Equation. Let’s choose 500 MHz for our example. Show the result in a table in the display panel. Here, we see that at 500 MHz, the device is clearly not unilateral. The unilateral approximation w