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Application Note 016
 

APPLICATION NOTE 016

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USING MODELITHICS CLR LIBRARY MODELS IN SHUNT CONNECTIONS

 
 


CIRCUIT DESCRIPTION

Modelithics’ CLR models are accurate for use in either series or shunt connection within a design. This application note discusses the use of Modelithics CLR Library Microwave Global Models™ in shunt configuration. Depending on the format of the shunt connection in the design, the model advanced pad features should be set accordingly. Several common configurations are presented, including a case where electromagnetic (EM) co-simulation is being used. The default mode for CLR models in the Modelithics library have solder mount pads included, with the reference planes at the outer edges of the component pad stacks (Figure 1).


Figure 1 – The default model setting (Sim_mode=0) has pads included and reference planes are located at the outer edges of the component pad stacks.

SHUNT COMPONENT WITH PAD EXTENDING OFF LINE

For all shunt connections, a microstrip tee element is used to establish the shunt component connection pin. The first shunt layout option has a component attached to a line in shunt with component pad stacks included and extending off the edge of the line. One pad is attached to the side of the line (at a connection point where the microstrip tee is placed) and the other pad is attached to ground. A layout image and schematic representation example for this shunt configuration is shown in Figure 2. In this connection, there is additional metal from the component pad extending from the line. Note that the value for W3 of the microstrip tee-junction (MTEE in ADS as shown) is set equal to the width of the component pad stack (Pad_Width), as is the width on one side of the step element (MSTEP) used at the component-via pad junction. W1 and W2 of the MTEE are equal to the line width. The advanced pad settings of the model to achieve the shunt connection shown in Figure 2 are:



Sim_Mode = 0 (default)
Pad_Mode = 0 (defaults to “pads included in layout” per Sim_Mode setting)
PadAngle (1 and 2) = 0 degrees (default)
PadInModel (1 and 2) = 100% (default)


Care should be taken to use an accurate representation of the ground via; the designer may choose to use an EM simulation data file to represent the via rather than use a built-in model.


Figure 2 – Layout (left) and schematic representation (right) for a shunt connection with pads off of the line. Pad stacks are outlined in dashed yellow line.

SHUNT COMPONENT WITH PART MOUNTED ON THE LINE

Another way to attach a shunt component is with one terminal of the part mounted on the line such that there is no extra metal extending from the line where the shunt component is attached. A layout and schematic image of this configuration is shown in Figure 3. An application where this connection type might be used is on the input/output lines of an amplifier design where shunt capacitors and/or inductors are commonly added. Figures 4 (LNA) and 5 (PA) show example test fixtures with shunt components attached such that one terminal is attached to the RF line with no additional pad stack extending from the line. A new feature added to the CLR models, starting with the Modelithics Library v17.5, significantly facilitates this common configuration. The new feature is part of the PadInModel parameter available in most CLR models as the added setting option: “Shunt: Part mounted on microstrip line”. This can be set for each pad individually. The advanced pad settings of the model to achieve the shunt connection shown in Figure 3 are:


Sim_Mode = 0 (default)
Pad_Mode = 0 (defaults to “pads included in layout” per Sim_Mode setting)
PadAngle1 = 0 degrees (default)
PadInModel1 = Shunt: Part mounted on microstrip line.
PadAngle2 = 0 degrees (default)
PadInModel2 = 100% (default)

Note if it is desired to have the grounded end component terminal mounted on the ground pad metal as well (no additional pad), the PadInModel parameter for the other model port can also be set to “Shunt: Part mounted on microstrip line.”


Figure 3 – Alternative shunt interconnection, in which one terminal of the component is mounted on the MLIN. The PadInModel1 parameter was changed from 100% to “Shunt: Part mounted on microstrip line.” Pad stacks are outlined in dashed yellow line.


Inductor and capacitor added in shunt on RF lines
Figure 4 – LNA evaluation board circuit (from Modelithics App Note 040) with components added in shunt with one terminal of the component mounted directly on the line.


Figure 5 – PA circuit (from Modelithics Presentation “Practical Broadband Power Amplifier Design Method Using Load-line, Load-pull And Real-frequency Synthesis Techniques”) showing components added in shunt with one terminal of the component mounted directly on the line.

The plot in Figure 6 shows a comparison of simulated S21 of the two different shunt configurations described above, where “Case 1” is a simulation of the part mounted in shunt with pads extending off of the line, and “Case 2” is a simulation of the part mounted in shunt with one component terminal on the line (no pad extending from line). The measurement trace shown is for one sample of the 2.0pF CBR04 capacitor mounted on a fixture in shunt configuration with one end of the component on the RF line (Case 2). Note the shift in resonance by ~560MHz due to the different shunt configuration and pad effect.


Figure 6 – S21 (dB) of CAP-KEM-0402-004 2.0pF capacitor model in two shunt configurations: Case 1: Pad off the line (Black), and Case 2: Component mounted on the line (Red) as well as one measured sample (Blue Circles) of the KEMET CBR04 2.0pF capacitor on fixtures with Case 2 configuration.

The plots in Figure 7 show S-parameters and phase of the same comparison, but with three measured samples



Figure 7 – S11 and S21 (dB) [top plots], and S11/S21 phase (degrees) [bottom plots] of CAP-KEM-0402-004 2.0pF capacitor model in two shunt configurations: Case 1: Pad off the line (Black), and Case 2: Component mounted on the line (Red) , as well as three measured sampled ( Blue , Pink , Turquoise ) of the capacitor on fixtures with Case 2 configuration.

SHUNT COMPONENT WHEN USING EM CO-SIMULATION

The third option for setting up the schematic and model pad parameters applies when doing EM co-simulation with Modelithics built-in pads and the respective advanced pad parameter settings. The pad parameters need to be set such that the pad parasitics are not counted twice; i.e. in both the layout EM simulation and circuit simulation. The recommended steps for an EM co-simulation are as follows, illustrated in Figure 8:


1) Model parameter settings for shunt configuration with one (or both) part terminals on a line (Case 2, with one terminal on a line):
Sim_Mode = 0 (default)
Pad_Mode = 2 (Pads not in Layout)
PadAngle1 = 0 degrees (default)*
PadInModel1 = Shunt: Part mounted on microstrip line.
PadAngle2 = 0 degrees (default)*
PadInModel2 = 100% (default)
2) Generate layout and run EM-simulation.
3) Using the same model settings, run the circuit co-simulation with the EM layout. The recommended design simulation is complete. Figure 9 shows a model-to-measurement comparison using EM co-simulation. *Only proceed to the next step if the ADS layout will be used to generate drawings for board fabrication.
4) The layout needs to be updated if it will be used to generate PCB fabrication drawing for board ordering. For the electronic simulation, the Modelithics model pads were removed from the layout and calculated in the circuit simulation. To generate a new layout for fabrication, change the Modelithics model Pad_mode setting to 0 (default based on Sim_mode) or 1 (Pads always in the layout). Update the layout. This version will now include the Modelithics model pads and can be used for fabrication.


Figure 8 – Steps for EM co-simulation using “Shunt: Part mounted on microstrip line” PadInModel feature. 1) Model pad parameter settings, 2) Layout for EM-simulation, 3) EM co-simulation, 4) Updated pad parameter settings for fabrication layout (if needed). (*Microstrip lines on either side of the Tee are added for visual representation of the line, but not used in simulation.)



circuit Simulation, Sim_mode=0, Shunt Mode
EM Co-Simulation, Sim_mode=0, Shunt Mode
Measured Data


Figure 9 - S21 (dB) of CAP-KEM-0402-004 2.0pF capacitor model in shunt configurations with one terminal of the capacitor mounted on a line (Case 2). Red=Circuit simulation , Pink=EM co-simulation (both with Sim_mode=0, Pad_mode=2 and PadInModel1= Shunt: Part mounted on microstrip line), and one measured sample (Blue Circles) of the KEMET CBR04 2.0pF capacitor on fixtures with Case 2 configuration.

Modelithics Characterization And Modeling Service

Each Modelithics Model Library contains up-to-date, measurement-based models that are fully integrated with leading electronic design automation (EDA) software. The models include complete documentation detailing the test fixtures used, measurement conditions, and modelto- measurement data comparisons. Model types include surface mount and integrated passives, diodes and multiple bipolar and field-effect transistor technologies. Modelithics also provides RF, microwave and mm-wave characterization and modeling services customized to your application. Our state of the art test and measurement equipment, plus years of experience, allow us to measure a wide variety of component and system parameters, including: S-parameters, IV characteristics, load pull, and noise characteristics. High-power testing services are also available.

About This Note

This application note was developed by Laura Levesque, Eric O’Dell, Isabella Bedford and Hugo Morales of Modelithics, Inc.

Contact Information

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