- Matching problems are specified in real-frequency format.
- Data can be imported from "*.s1p" or "*.s2p" files.
- The target impedance at each frequency can be a point inside the Smith Chart (point-match), any point on the circumference of a Smith Chart circle (circle match), or the area inside or outside such a circle. The circles of interest could be constant gain or constant noise figure circles, or circular approximations of areas defined by load-pull measurements.
- In narrowband problems, control over the input or output impedance of the matching network at the 2nd and 3rd harmonic frequencies is provided. A range of target reactance values can be specified at each harmonic frequency. Control over the resistance at the harmonics frequencies is also provided in order to minimize power generation at these harmonic frequencies.
- A wizard is provided to assist with making the specifications for distributed or microstrip solutions.
- Solutions are synthesized by doing synthesis-based systematic searches.
- The search can be done globally over different topologies.
- The search can be unconstrained or can be constrained to low-pass or high-pass topologies, or topologies without any series capacitors or without any shunt inductors.
- The search can be constrained to solutions suitable for inter-stage biasing (four or more element are required in this case).
- A number of the best solutions obtained in the search are optimized.
- Up to 8 elements can be used in the matching networks synthesized.
- Solutions can be displayed or printed or copied to the clipboard. When microstrip solutions are required, the artwork of each solution can also be displayed.
- The input and output impedance of each matching network can be displayed graphically or in tabular form. When the harmonic impedances were controlled, the impedance at the harmonic frequencies can also be displayed.
- A worst-case tolerance analysis is done on the solutions provided. Preference should be given to insensitive solutions.
- Artwork editing capabilities are provided. When lines are curved or meandered the physical line lengths are adjusted automatically to preserve the electrical performance.
Each solution can be exported as
- An Amplifier Design Wizard (Ampsa ADW) circuit file
- A Microwave OfficeTM script.
- A DXF or HPGL file
- A TouchstoneTM netlist
- A Super CompactTM netlist
The following types of matching networks can be synthesized:
- Lumped-element networks.
- Distributed matching networks.
- Mixed lumped/distributed matching networks.
Parasitic inductance and capacitance can be specified for the capacitors and inductors used in lumped or mixed lumped/distributed solutions. The values of any lumped-elements used can also be constrained. It is a good idea to initially leave these values unconstrained.
Commensurate (equal line length) and non-commensurate networks can be synthesized. In both cases connecting lines can be added to the input and/or the output ports to ensure that all the solutions obtained will effectively start and end with series elements. Short-circuited and open-ended stubs can also be added for biasing or harmonic control purposes.
- The characteristic impedances (lines widths) are fixed and must be specified by the user. High characteristic impedances are usually used for the main-line sections and any short-circuited stubs, while low characteristic impedances are usually used for any open-ended stubs.
- Different characteristic impedance values (line widths) can be specified for main-line sections, shorted stubs and open-ended stubs.
- The characteristic impedance (line widths) of the main-line sections can be tapered (power matching problems). The initial and final characteristic impedance values to be used must be specified by the user.
- The line lengths are used as variables. The lengths of the main-line sections can be constrained.
- Wide stubs can be replaced automatically with stepped main-line sections during synthesis.
- When microstrip solutions are required, the short-circuited stubs can be terminated with vias or inductors (bond wires).
- When microstrip solutions are required, a rendering of the line widths and the minimum and maximum lengths of the main-line sections is displayed graphically for verification purposes.
- When microstrip solutions are required, the electrical parameters associated with the width and length specifications, as well as the associated T-junctions are also calculated and can be displayed. In order for the microstrip performance to closely approximate the desired electrical performance, the stub widths should be chosen to minimize the transformer and shunt susceptance loading effects associated with the T-junctions. Line losses should be taken into account when the minimum line width is specified.
- The line lengths are fixed, while the characteristic impedances are used as variables. Different line lengths can be used for the main-line sections, the open-ended stubs and the short-circuited stubs. It is a good idea to experiment with different line lengths when a new problem is solved.
- The lowest and highest characteristic impedances allowable must be specified. Different constraints can be imposed on the characteristic impedance values of the main-line sections, the open-ended stubs and the short-circuited stubs.
- The characteristic impedance values can be left unconstrained initially. This is useful for establishing an appropriate range of characteristic impedance values for the problem to be solved. The information obtained should also be used when the substrate to be used is selected.
- The length option can be used to force the lengths of any stubs used to be electrically short. The stub impedance/susceptance will approximate that of the equivalent lumped component closely if this is done. This opens the possibility of replacing the stubs in the solutions synthesized with lumped components.
- The non-commensurate distributed synthesis approach is followed, but the line lengths are reduced by using lumped inductors and/or capacitors when the required values are within the constraints specified. Shunt capacitors can also be replaced with overlay capacitors. Allowance is made for the associated line effect and via inductance when this option is selected.
- Open-ended stubs can be replaced with stepped main-line sections. This option is frequently useful when matching networks for power amplifiers are synthesized.
- Pads can be specified for the lumped components used in distributed solutions. The default pad sizes used for different chip sizes can be modified by the user.
- An extra connecting line can be specified for stubs. This option can be used to separate the shunt component pad from the main-line junction. The parasitic effects associated with the corresponding T-junctions can be reduced by using this option. It may also be required for solder reflow purposes.
- A rendering of the microstrip specifications, which includes the pad sizes, is displayed graphically for verification purposes.
- Parasitic inductance can also be specified for the capacitors used, while parasitic capacitance can be specified for the inductors used.
The microstrip models used in the standard version of the Impedance-Matching Wizard is based on work done by Hammerstad and Jensen . To get accurate results at millimeter frequencies and in high power (low impedance) circuits it may be necessary to customize the microstrip discontinuity models used. Provision is made in the IMW for user customization of these models. Such customization is based on EM-simulations of the relevant discontinuities on the substrate of interest. Models must then be fitted to the EM data, after which curves must be fitted to the relevant model parameters over the frequency range of interest.
The matching networks synthesized with the Impedance-Matching Wizard can be processed further in the Amplifier Design Wizard (Ampsa ADW). This processing includes comprehensive optimization of the solutions selected, replacing inductors with square spiral inductors, hair-pin inductors, solenoidal coils or bond wires (single or double geometrical bond wires are supported), and replacing capacitors with series or shunt single-layer parallel-plate capacitors (chip capacitors, MIM capacitors, etc.). Overlay capacitors with centered or offset vias can also be used. When offset vias are used, one or two vias can be used.
Note that more optimization features are provided in the Impedance-Matching Module of the ADW than in the IMW. The solutions synthesized can be optimized in terms of the active performance targeted in the ADW environment. A wide range of impedance-matching problems can also be set up automatically in the ADW.
The artwork can be manipulated extensively in the ADW. In addition to the export formats allowed in the Impedance-Matching Wizard, native Sonnet Software® files can also be created for the ADW artwork. When the artwork is exported in DXF format for use in CST’s Microwave StudioTM a CST technology file is also created. This file is used to extrude the different layers in the artwork at the correct heights. The DXF layers are also mapped to the required CST materials. Footprints are also created for any bond wires used.
It is sometimes not possible to solve a defined matching problem well (theoretical gain-bandwidth limitations). Frequency selective resistive networks can then be used to modify the problem appropriately. Double-section modification networks can be synthesized in the ADW to reduce gain-bandwidth constraints before a lossless matching network is synthesized. These modification networks can also serve to level gain slopes and to reduce or remove stability problems in amplifiers.
In addition to customization of microstrip discontinuities, provision for customization of the single-layer parallel plate capacitor models and the square spiral inductor model is also made in the ADW.
- 1. E. Hammerstad and O. Jensen, "Accurate Models for Microstrip Computer- Aided Design" IEEE MTT-S, International Symposium Digest, Washington D.C., May 1980, pp. 407-409.