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1 Agilent EEsof EDA This document is owned by Agilent Technologies, but is no longer kept current and may contain obsolete or inaccurate references. We regret any inconvenience this may cause. For the latest information on Agilent s line of EEsof electronic design automation (EDA) products and services, please go to:

Eagleware App Note 23 Using GENESYS to Generate Load Pull Data Abstract For many circuits that involve active devices, the performance is sensitive to the load.

2 Eagleware App Note 23 Using GENESYS to Generate Load Pull Data Abstract For many circuits that involve active devices, the performance is sensitive to the load. A common way of characterizing this performance is known as load pull. Contours of particular values of the performance measure are generated over a range of loads. Both the real and imaginary parts of the load are varied. The results are commonly displayed on a Smith chart. Since most of these circuits can be designed with GENESYS, it is convenient to be able to generate and plot load pull data within this environment. Introduction For many RF circuits, there may be considerable variation in the load. To determine the sensitivity of various performance measures to these load variations, GENESYS supports parameter sweeps of both the real and imaginary parts of the load. These load impedances are independent of frequency. Therefore, the designer does not need to formulate equivalent reactive elements for each frequency of interest. The results of the parameter sweeps are available in tabular form or can be plotted on a Smith chart. The tables of data can be written to a file for external manipulation. The Smith chart presents contours of user selected values of the performance measure of interest. Analysis Procedure The first step is to replace the existing load in the schematic with the schematic element called Frequency-independent Impedance (IMP). The two input parameters for this element are the real part (R) and the imaginary part (X) of the impedance. Since these will be defined in the Equations, we use variable names Zreal and Zimag respectively. The resulting schematic will be as shown in the schematic above. This example can be found on the Eagleware web site on the Applications forum. A simple

3 transistor amplifier is driven by a 30 dbm input signal at 1.0 GHz. The transistor is a generic nonlinear NPN model using default parameters. The dc operating point is set by the 5 volt supply and the 500Ω resistor R1. In this case, the performance measure of interest is the output voltage (Vout) at the test point Out at the frequency of the fundamental. The second step is to set up the Equations which will define the swept variables (Gamma_real, Gamma_imag), the complex impedance (Zreal, Zimag), the output variable, in this case Vout), and the desired outputs (contours, points). For this example, the resulting Equations are shown below. Equations for Example Case Setup up load to sweep, in terms of Gamma Gamma_real =?0.5 Gamma_imag =?0.5 Gamma = complex(gamma_real,gamma_imag) Convert Gamma to Z, limit Real part of Z to greater than 0 Z = 50*(1-gamma)/(1+gamma) Zreal = re(z) Zimag = im(z) if Zreal < 0.1 then Zreal = 0.1 Set power level Pin=-30 Calculate Contours for example parameter, Vout note: the contour function allows setting start, stop levels for contours as well as smoothing parameters see the on-line help for details using real.sch1 Vout=.db[vout]@#1 Vmax = 15 Vmin = -2.5 Vstep=2.5 smooth=0 Y_max=1 Y_min=-1 X_max=1 X_min=-1 contours=contour(vout,vmin,vmax,vstep,smooth,x_min,x_max,y_min,y_max) points=plotpoints(vout) The swept variables (Gamma_real, Gamma_imag) will be controlled by two parameter sweeps Imag and Real. Therefore, the variables are set to be tunable by the use of 2004 Eagleware Corporation 2

4 ? before the value. The value of 0.5 is arbitrary. The complex variable Gamma (γ) is formed by the equation: Gamma = complex(gamma_real,gamma_imag) The swept variables define a grid of points in a complex plane. This grid is related to the load impedance and the impedance plotted on a Smith chart by the equations: Z = 50*(1-gamma)/(1+gamma) Zreal = re(z) Zimag = im(z) if Zreal < 0.1 then Zreal = 0.1 The origin of this complex plane is the center of the Smith chart, which corresponds to the Reference impedance (Zo). Typically, this is a real impedance (Ro) of 50Ω. For a sweep of the real and imaginary parts of γ of ± 0.70, the grid of points is as shown. This choice of Gamma keeps the impedances within the Smith chart, assuring that the real part of the impedance is positive (i.e. the load is passive). Alternately, a range of ± 0.90 can be used, where the equations force the real part of the impedance to be positive. The choice can be based on the range of load impedances expected. For the ± 0.70 range, the pure real impedances will range from 8.8 Ω (γ = 0.7) to 283 Ω (γ = -0.7). For the range of reactive loads with a real part (Ro) equal to 50 Ω, the extremes are ± 47 Ω. And finally, at the boundaries of the Smith chart where the real part of the impedance is essentially zero, the reactances are: 20.7 Ω and Ω. The final set of equations defines the output variable and the data to be plotted. While contours can be generated for any output parameter (for example, gain or intermodulation), in this example we will graph the output voltage, Vout. The output is the voltage across the load, as defined by: Vout=.db[vout]@#1 The measurement is.db[ ] which yields the result in db, and denotes the first frequency or fundamental (i.e. 1 GHz). The remaining equations give the values of the parameters for the plotting of the curves and points on the Smith chart. Vmax = 15 Value of Vout on maximum value contour Vmin = -2.5 Value of Vout on minimum value contour Vstep = 2.5 Incremental step between maximum and minimum contours smooth = 0 Indicates no smoothing to be applied to contour curve Y_max = 1 Maximum vertical scale for Y_min = -1 Minimum vertical scale for X_max = 1 Maximum (right-most) scale for X_min = -1 Minimum (left-most) scale for Contours = CONTOUR(Vout, Vmin, Vmax, Vstep,smooth,X_min,X_max, Y_min,Y_max) Points = PLOTPOINTS(Vout) The first 3 parameters control the values of the output variable (Vout) for each of the curves. In this case the curves will represent Vout = -2.5 db, 0 db, +2.5 db, db. The scaling parameters will inhibit plotting outside a square of length 2 on a side. This is the square for which the Smith chart boundary is the inscribed circle. Note that any curves outside the Smith chart are not valid points, since we forced the real part of the impedance to be zero Eagleware Corporation 3

5 The resulting Smith chart is shown. Notice that both the contours of constant Vout, and the points where the data was taken are displayed. Markers were added manually along the real or horizontal axis, to show the values of Vout for each curve. This horizontal axis corresponds to impedances with a positive real part only. The third step of the process is to set up the three analyses: Harmonic Balance (HB1), Sweep Imag, and Sweep Real. The parameters for each analysis are as follows: 1. Harmonic Balance (HB1): Design to simulate: Sch1 Signal: frequency = 1000 MHz, order = Eagleware Corporation 4

2. Sweep Imag : Simulation to sweep = HB1 Variable to sweep = Gamma_Imag Type of sweep = Linear: Number of Points = 15 Sweep Range: Start Value = -0.7, Stop Value = 0.7 3.

6 2. Sweep Imag : Simulation to sweep = HB1 Variable to sweep = Gamma_Imag Type of sweep = Linear: Number of Points = 15 Sweep Range: Start Value = -0.7, Stop Value = Sweep Real : Simulation to sweep = Imag Variable to sweep = Gamma_Real Type of sweep = Linear: Number of Points = 15 Sweep Range: Start Value = -0.7, Stop Value = 0.7 An optional step is to generate a table of the points where the performance was evaluated, and the points on the contours of constant Vout. This Table can be exported as a file for further evaluation by a program such as EXCEL. The first several lines of the tabular output are shown below. Conclulsion The GENESYS environment is capable of generating load pull analyses for a wide range of circuits of importance to RF and microwave engineers. This example has demonstrated the relatively simple steps required to perform such an analysis. It also indicated the use of parameter sweeps, nonlinear simulations, and the export of tabular data Eagleware Corporation 5

7 For more information about Agilent EEsof EDA, visit: Agilent Updates Get the latest information on the products and applications you select. Agilent Direct Quickly choose and use your test equipment solutions with confidence. For more information on Agilent Technologies products, applications or services, please contact your local Agilent office. The complete list is available at: Americas Canada (877) Latin America United States (800) Asia Pacific Australia China Hong Kong India Japan 0120 (421) 345 Korea Malaysia Singapore Taiwan Thailand Europe & Middle East Austria Belgium 32 (0) Denmark Finland 358 (0) France * *0.125 /minute Germany ** **0.14 /minute Ireland Israel /544 Italy Netherlands 31 (0) Spain 34 (91) Sweden Switzerland United Kingdom 44 (0) Other European Countries: Revised: March 27, 2008 Product specifications and descriptions in this document subject to change without notice. Agilent Technologies, Inc. 2008

EM Insights Series. Episode #1: QFN Package. Agilent EEsof EDA September 2008

EM Insights Series. Episode #1: QFN Package. Agilent EEsof EDA September 2008 EM Insights Series Episode #1: QFN Package Agilent EEsof EDA September 2008 Application Overview Typical situation IC design is not finished until it is packaged. It is now very important for IC designers