Andy HowardApplications Engineer28 May, 2002,Load Pull Simulation Using ADS,Load Pull Simulation Using ADS 28 May, 2002,Page 2,Outline,Overview Specifying and generating desired load reflection coefficients Assigning arbitrary reflection coefficients at the harmonic freqs. Biasing the device and running a simulation Calculating desired responses (delivered power, PAE, etc.) Generating contour lines,,Load Pull Simulation Using ADS 28 May, 2002,Page 3,Load pull simulation varies the load reflection coefficient presented to a device...,Vary load reflection coefficient,,Load Pull Simulation Using ADS 28 May, 2002,Page 4,to find the optimal value to maximize power or PAE, etc.,Load Pull Simulation Using ADS 28 May, 2002,Page 5,Specify the load reflection coefficients,Simulation set up is complicated, but region is sampled more uniformly,Simulation set up is trivial,Load Pull Simulation Using ADS 28 May, 2002,Page 6,Sweeping rho over a circular region,Specify circular region, via s11_rho and s11_center variables,This is just a static figure. It does not get updated nor correspond to the values in the equations.,,Radius of circle,,Center of circle,Load Pull Simulation Using ADS 28 May, 2002,Page 7,Use ReflectionCoefUtility data display to help set s11_center and s11_rho,The circle center and radius are updated when you move either or both of the markers,Load Pull Simulation Using ADS 28 May, 2002,Page 8,Two variables are swept to generate the points within the desired circle,,,These initialize the swept variables,,,indexs11 is the reflection coefficient,Will explain Start and Stop equations later,,Load Pull Simulation Using ADS 28 May, 2002,Page 9,More on the swept variables,,,Variable “imag_indexs11” is the y-axis value of simulated reflection coefficient. Variable “real_indexs11” is the x-axis value. The imag_indexs11 variable is stepped uniformly, whereas real_indexs11 is stepped non-uniformly.,Each point is a data pair: (real_indexs11, imag_indexs11),m3 is at approximately: (-0.706, 0.386),Load Pull Simulation Using ADS 28 May, 2002,Page 10,Sweep limits for “imag_indexs11”,,Arrow points to s11_center,,,imag(s11_center),,,A,B,Distance “A”=Distance “B”=max_rho-max_rho/(lines+1),Load Pull Simulation Using ADS 28 May, 2002,Page 11,What is “max_rho”?,,,Length of vector C =mag(s11_center),C,D,Length of vector D =1-mag(s11_center),The max_rho equation reduces the radius of the circle of simulated reflection coefficients if any part of the circle would otherwise be outside the Smith chart, which would imply an active load.,,“max_rho” will be the smaller of the length of vector D and the user- entered circle radius, s11_rho.,Load Pull Simulation Using ADS 28 May, 2002,Page 12,What about the “max_rho/(lines+1)” term?,,,Including this term prevents the first and last line from being tangent to the circle at a single point. This allows real_indexs11 to be swept along the first and last lines defined by imag_indexs11.,Load Pull Simulation Using ADS 28 May, 2002,Page 13,maximum value of c_limit,Sweep limits for “real_indexs11”,,Arrow points to s11_center,,real(s11_center),,c_limit is the distance from the vertical center line of the circle to the edges, along each of the horizontal lines. It is different for each horizontal line.,,,,,,min. value of c_limit,,Load Pull Simulation Using ADS 28 May, 2002,Page 14,How is c_limit calculated?,,Arrow points to s11_center,imag(s11_center),c_limit is calculated from: r**2=c_limit**2+Y**2, where Y=imag_indexs11-imag(s11_center), and r=max_rho,,,,Circle radius is max_rho,,,,,,imag_indexs11,,c_limit,,Load Pull Simulation Using ADS 28 May, 2002,Page 15,How are the number of lines and the points per line calculated?,,User sets this value,,The “lines” equation takes the square root of “pts”, then computes the integer part. The max() function ensures that at least one line is used. The number of points per line is computed by keeping the integer part of pts/lines.,Load Pull Simulation Using ADS 28 May, 2002,Page 16,Alternate reflection coefficient sweep,Sweep the phase of the reflection coefficient “Phi_rho” in degrees, and sweep the magnitude “Mag_rho”. “rho” below becomes the swept reflection coefficient, instead of indexs11.,Load Pull Simulation Using ADS 28 May, 2002,Page 17,Outline,Overview Specifying and generating desired load reflection coefficients Assigning arbitrary reflection coefficients at the harmonic freqs. Biasing the device and running a simulation Calculating desired responses (delivered power, PAE, etc.) Generating contour lines,,Load Pull Simulation Using ADS 28 May, 2002,Page 18,You could make the load independent of frequency:,But this would model an unrealistically simple situation and would give sub-optimal results.,Load Pull Simulation Using ADS 28 May, 2002,Page 19,Set source and load impedances at harmonic frequencies arbitrarily,These default values are somewhat sub-optimal, as using opens or shorts to terminate the harmonics should give better performance.,Z。