An Overview of RF Circuit Simulation - Revision history

Kazem Sabet: /* Physical Transmission Lines */

2016-11-10T15:33:12Z

‎Physical Transmission Lines

Kazem Sabet: /* Generic T-Line Discontinuities */

2016-11-10T15:30:46Z

‎Generic T-Line Discontinuities

Kazem Sabet: /* Physical Transmission Line Discontinuities */

2016-11-10T15:30:24Z

‎Physical Transmission Line Discontinuities

Kazem Sabet: /* Physical Transmission Line Discontinuities */

2016-11-10T15:29:29Z

‎Physical Transmission Line Discontinuities

Kazem Sabet: /* Generic T-Line Discontinuities */

2016-11-10T15:29:00Z

‎Generic T-Line Discontinuities

Kazem Sabet: /* Generic Transmission Lines */

2016-11-10T15:28:36Z

‎Generic Transmission Lines

Kazem Sabet: /* The Complex Impedance Device */

2016-11-10T15:27:29Z

‎The Complex Impedance Device

Kazem Sabet: /* Defining S-Parameters */

2016-11-10T15:27:06Z

‎Defining S-Parameters

Kazem Sabet: /* Multiport Networks */

2016-11-10T15:26:47Z

‎Multiport Networks

Kazem Sabet: /* Understanding RF Circuit Analysis as an Analog Simulation */

2016-11-10T15:26:20Z

‎Understanding RF Circuit Analysis as an Analog Simulation

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 The physical transmission line types are characterized by their physical dimensions and material properties.
 === Physical Line Calculators and Designers ===
 When you place a generic T-line part in your circuit, you have to specify its characteristic impedance (Z0), effective permittivity (eeff) and attenuation constant (alpha). In the case of physical transmission line parts like mircostrip, coaxial line or CPW, you specify the physical parameters of the line such as various dimensions and material properties. [[RF.Spice A/D]] then automatically calculates the necessary transmission line parameters at the time of simulation based on your physical data.
 For every physical transmission line type listed above, the '''Device Manager''' of [[RF.Spice A/D]] provides a corresponding '''Line Calculator'''. The line calculators are accessible form the '''Tools Menu''' of the Device Manager. The line calculators take the substrate properties and the physical dimensions of a line types and calculate its characteristic impedance (Z0) and effective permittivity (eeff). The Line Calculator dialog also has an "Operational Frequency" input with a default frequency of 1GHz, which is used to calculate the guide wavelength of the transmission line at that frequency. In many practical applications, you need quarter-wavelength line segments. In that case, you must first calculate the guide wavelength of the transmission line as defined by &lambda;<sub>g</sub> = &lambda;<sub>0</sub> / &radic;&epsilon;<sub>eff</sub>, where &lambda;<sub>0</sub> = c/f is the free space wavelength at the operational frequency.
@@ Line 248: / Line 254: @@
 <tr>
 <td>
-[[File:tline10.png|thumb|350px| CPW Line Calculator.]]
+[[File:tline10.png|thumb|left|480px| CPW Line Calculator.]]
 </td>
 <td>
-[[File:tline12.png|thumb|350px| Coaxial Line Calculator.]]
+[[File:tline12.png|thumb|lrft|480px| Coaxial Line Calculator.]]
 </td>
 </tr>
 </table>
 You often need to design a 50&Omega; transmission line of a certain type. [[RF.Spice A/D]] provides ten physical transmission line design tools for:
@@ Line 269: / Line 276: @@
 * Twin-Lead Line
 * Twisted-Pair Line
 The above line designers ignore the conductor and dielectric losses and calculate the physical dimensions of the line for a given value of the characteristic impedance Z0. For example, given a substrate with thickness h and relative permittivity &epsilon;<sub>r</sub>, the "Microstrip Designer" calculates the microstrip width in mm for a given value of Z0 (50 Ohms by default). Some line type like CPW and coaxial line have more than one dimensional parameter that can be varied. For example, CPW has slot width (w) and center strip width (s), while coaxial line has inner and outer conductor radii. In such cases, the line designer dialog provides radio button options to fix one parameter and vary the other.
@@ Line 275: / Line 290: @@
 <tr>
 <td>
-[[File:tline11.png|thumb|350px| CPW Line Designer.]]
+[[File:tline11.png|thumb|left|480px| CPW Line Designer.]]
 </td>
 <td>
-[[File:tline13.png|thumb|350px| Coaxial Line Designer.]]
+[[File:tline13.png|thumb|left|480px| Coaxial Line Designer.]]
 </td>
 </tr>

@@ Line 202: / Line 202: @@
 <tr>
 <td>
-[[File:tline4.png|thumb|left|550px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
+[[File:tline4.png|thumb|left|720px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
 </td>
 </tr>

@@ Line 292: / Line 292: @@
 <tr>
 <td>
-[[File:tline5.png|thumb|left|640px| The schematic symbols of the some Physical Transmission Line Discontinuity devices. (Top Row) microstrip components: right-angled bend, mitered bend, tee and cross junctions, (Bottom Row) CPW components: open end, short end, gap and step junction.]]
+[[File:tline5.png|thumb|left|720px| The schematic symbols of the some Physical Transmission Line Discontinuity devices. (Top Row) microstrip components: right-angled bend, mitered bend, tee and cross junctions, (Bottom Row) CPW components: open end, short end, gap and step junction.]]
 </td>
 </tr>

@@ Line 292: / Line 292: @@
 <tr>
 <td>
-[[File:tline5.png|thumb|480px| The schematic symbols of the some Physical Transmission Line Discontinuity devices. (Top Row) microstrip components: right-angled bend, mitered bend, tee and cross junctions, (Bottom Row) CPW components: open end, short end, gap and step junction.]]
+[[File:tline5.png|thumb|left|640px| The schematic symbols of the some Physical Transmission Line Discontinuity devices. (Top Row) microstrip components: right-angled bend, mitered bend, tee and cross junctions, (Bottom Row) CPW components: open end, short end, gap and step junction.]]
 </td>
 </tr>

@@ Line 202: / Line 202: @@
 <tr>
 <td>
-[[File:tline4.png|thumb|left|480px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
+[[File:tline4.png|thumb|left|550px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
 </td>
 </tr>

@@ Line 150: / Line 150: @@
 === The Generic T-Line ===
 [[RF.Spice A/D]] offers a passive device called Generic T-line with the keyboard shortcut “T”, which is a general purpose frequency-domain transmission line segment model. It is based on the native SPICE LTRA model, but with the following parameters:
@@ Line 159: / Line 158: @@
 The default parameters of the Generic T-Line are Z0 = 50 Ohms, eeff = 1, alpha = 0, and len = 10mm. A unit effective permittivity implies a TEM transmission line because &radic;&epsilon;<sub>eff</sub> = &beta; / k<sub>0</sub>, where &beta; is the propagation constant of the transmission line and k<sub>0</sub> = 2&pi;f/c is the free space propagation constant, with f being the frequency in Hertz and c = 3e8 m/s being the speed of light. A zero attenuation constant represents a lossless transmission line. The Generic T-Line device is indeed a two-port network with a 2&times;2 scattering matrix or four S-parameters: s11, s21, s12 and s22. Obviously, this is a reciprocal and symmetric network, i.e., s11 = s22, and s21 = s12.
 Note that N-port networks in [[RF.Spice A/D]] have schematic symbols with 2N pins. Each pair of pins represents a port. In a similar way, the generic T-line has two ports and four pins. The pins are marked with plus and minus signs. For example, in the figure above, the pins P1+ and P1- together form Port 1. Normally, the negative pins are grounded, and the positive pins are connected to the other parts of the circuit.
@@ Line 171: / Line 178: @@
 <tr>
 <td>
-[[File:tline2.png|thumb|400px| The schematic symbols of the Generic Open Stub (left) and Generic Short Stub (right) devices.]]
+[[File:tline2.png|thumb|left|480px| The schematic symbols of the Generic Open Stub (left) and Generic Short Stub (right) devices.]]
 </td>
 </tr>
@@ Line 195: / Line 202: @@
 <tr>
 <td>
-[[File:tline4.png|thumb|480px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
+[[File:tline4.png|thumb|left|480px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
 </td>
 </tr>

@@ Line 97: / Line 97: @@
 <tr>
 <td>
-[[File:twoport3.png|thumb|400px| The property dialog of the Complex Impedance device.]]
+[[File:twoport3.png|thumb|left|550px| The property dialog of the Complex Impedance device.]]
 </td>
 </tr>

@@ Line 77: / Line 77: @@
 <tr>
 <td>
-[[File:twoport2.png|thumb|400px| The property dialog of a multiport network device.]]
+[[File:twoport2.png|thumb|left|550px| The property dialog of a multiport network device.]]
 </td>
 </tr>

@@ Line 53: / Line 53: @@
 <tr>
 <td>
-[[File:twoport1.png|thumb|400px| Cascading two two-port network devices.]]
+[[File:twoport1.png|thumb|left|480px| Cascading two two-port network devices.]]
 </td>
 </tr>

@@ Line 5: / Line 5: @@
 == Understanding RF Circuit Analysis as an Analog Simulation ==
 You can use [[RF.Spice A/D]] to simulate or design distributed analog and mixed-mode circuits at high frequencies. RF circuit analysis, by nature, is an AC analysis that you typically run at high frequencies ranging from tens of Megahertz to tens of Gigahertz. At such high frequencies, the dimensions of your circuit may become comparable in order of magnitude to the wavelength, when wave retardation effects start to appear. In other words, your circuit starts to act like a distributed structure rather than a lumped circuit where signals propagate instantaneously. In the analysis of a low frequency circuit, two nodes that are connected to each other through a wire are assumed to have equal potentials or identical voltages. In RF circuits, however, parts and devices are connected to one another using transmission line segments, which introduce additional phase shifts depending on their electrical lengths and may also alter the voltages and currents at different points of the circuit due to impedance mismatch.
 [[RF.Spice A/D]] uses the same Berkeley SPICE and XSPICE simulation engines of its forerunner B2.Spice A/D. In other words, the high frequency AC analysis is carried out by the same analog and mixed-mode SPICE simulation engines based on nodal admittance analysis, which have been enhanced with additional RF simulation capabilities. As a result, you can mix the RF devices in your circuits with all the other analog and mixed-mode devices. You can also mix transmission-line-type RF devices with digital parts and perform mixed-mode time domain simulations.