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Oscillator QuickStart Guide

The Oscillator QuickStart Guide serves as a simple introduction to using the Oscillator DesignGuide. For more detailed reference information, refer to Oscillator DesignGuide Reference.

The DesignGuide is applicable to any oscillator, but is especially useful for RF Board and Microwave applications. It is designed to help both experts and novices to create designs of various complexity.

Note

This documentation is written describing and showing access through the cascading menu
preference. If you are running the program through the selection dialog box method, the appearance and interface will be slightly different.

Using DesignGuides

All DesignGuides can be accessed in the Schematic window through either cascading menus or dialog boxes. You can configure your preferred method in the Advanced Design System Main window. Select the DesignGuide menu.
The commands in this menu are as follows:
DesignGuide Studio Documentation > Developer Studio Documentation is only available on this menu if you have installed the DesignGuide Developer Studio. It brings up the DesignGuide Developer Studio documentation. Another way to access the Developer Studio documentation is by selecting Help > Topics and Index > DesignGuides > DesignGuide Developer Studio (from any ADS program window).
DesignGuide Developer Studio > Start DesignGuide Studio is only available on this menu if you have installed the DesignGuide Developer Studio. It launches the initial Developer Studio dialog box.
Add DesignGuide brings up a directory browser in which you can add a DesignGuide to your installation. This is primarily intended for use with DesignGuides that are custom-built through the Developer Studio.
List/Remove DesignGuide brings up a list of your installed DesignGuides. Select any that you would like to uninstall and choose the Remove button.
Preferences brings up a dialog box that allows you to:

  • Disable the DesignGuide menu commands (all except Preferences) in the Main window by unchecking this box. In the Schematic and Layout windows, the complete DesignGuide menu and all of its commands will be removed if this box is unchecked.
  • Select your preferred interface method (cascading menus vs. dialog boxes).

    Close and restart the program for your preference changes to take effect.

Note

On PC systems, Windows resource issues might limit the use of cascading menus. When multiple windows are open, your system could become destabilized. Thus the dialog box menu style might be best for these situations.

Accessing the Documentation

To access the documentation for the DesignGuide, select either of the following:

  • DesignGuide > Oscillator > Oscillator DesignGuide Documentation (from ADS Schematic window)
  • Help > Topics and Index > DesignGuides > Oscillator (from any ADS program window)

Basic Procedures

Access the Oscillator DesignGuide from the ADS Schematic window. Select Design Guide > Oscillator Design Guide , as shown here. All features of the Design Guide are available from the Oscillator DesignGuide menu.

The Guide contains the following:

  • Nine oscillator circuits (Generic Oscillator, Clapp Oscillator, Hartley Oscillator, Modified Clapp Oscillator, Modified Colpitts Oscillator, XTO, SAW, VCO, and YTO), containing ready-to-use typical oscillator structures for fixed frequency (XTO, SAW) and tunable (VCO, YTO) oscillators in various frequency ranges.
  • Component library (Components), providing useful building blocks for oscillator design.
  • Selection of circuits that simulate their behavior (Component Characterization), providing simulations that characterize 1-ports and 2-ports.

Note

Selection of a component brings a component into a design. All other selections (oscillators and component characterization) bring a circuit and simulation into a design (replacing a previous design).

Component Sub-menu Structure

The Components menu contains a small custom library of resonators and devices, which can help in either modifying an existing oscillator or assembling a new one. They include: device DC and S-parameter characteristics and resonator and filter S-parameter and impedance/admittance characteristics

Oscillator Sub-menu Structure

Select DesignGuide > Oscillator DesignGuide > Generic Oscillator and explore the entries in the cascading menu, as shown here.

Each Oscillator design is divided into two groups. large-signal measurements and linear/nonlinear design tools.
Easy-to-use large-signal measurements (for push-button nonlinear analysis), contain simulations of the following:

  • Single-frequency oscillations
  • Phase noise
  • Tuned oscillations
  • Frequency pulling
  • Frequency pushing

This group is recommended as starting point for both an expert and a novice user. For the expert, it provides an overview of tool capabilities. For the novice user, it provides a working oscillator together with simulations of its typical characteristics. You can choose either the Generic Oscillator, Clapp Oscillator, Hartley Oscillator, Modified Clapp Oscillator, Modified Colpitts Oscillator, or one of the examples (XTO, SAW, VCO, YTO) to start a desired application.
Linear and nonlinear design tools include Output Load Mapping, Input Load Mapping, Stability via Nyquist Plot, Nyquist Plot for Simple Circuit, Nyquist Plot for Active Resonator, and Large Signal S-Parameters.
These tools are intended as an aide in designing an oscillator from scratch and in gaining insight into an existing oscillator. The full choice of tools is contained in the Generic Oscillator. The examples use only those tools that are useful in their particular case. The full set of tools include the following:

  • Load mapping for load-to-resonator
  • Resonator-to-load
  • Nyquist stability criterion for varying Zo
  • Two additional examples (only in Generic Oscillator), explaining the role of Zo

For nonlinear designs, large-signal S-parameters are defined and applied to oscillator power and frequency prediction.

Tools Sub-menu Structure

These utilities provide added functionality to this DesignGuide. A brief description is provided for each. For more information select the help button located in each utility.

Transistor Bias Utility

The Transistor Bias Utility provides SmartComponents and automated-assistants for the design and simulation of common resistive and active transistor bias networks. The automated capabilities can determine the transistor DC parameters, design an appropriate network to achieve a given bias point, and simulate and display the achieved performance. All SmartComponents can be modified when selected. You simply select a SmartComponent and with little effort redesign or verify their performance.

Smith Chart Utility

This DesignGuide Utility provides full smith chart capabilities, synthesis of matching networks, allowing impedance matching and plotting of constant Gain/Q/VSWR/Noise circles. This guide assumes you have installed the associated DesignGuide with appropriate licensing codewords.

Impedance Matching Utility

The Impedance Matching Utility performs the synthesis of lumped and distributed impedance matching networks based on provided specifications. The Utility features automatic simulation, sensitivity analysis, and display setup to enable simple and efficient component verification.

Design Flow Example

Following is a simple design flow example for a fixed frequency oscillator.

Preliminary Steps

  1. Open ADS.
  2. Open a new or existing project.
  3. Open a new Schematic window.
  4. Select DesignGuide > Oscillator DesignGuide.
  5. Select Crystal Oscillator (XTO) > Stability via Nyquist Plot.

Important Preliminary Decisions

The schematic hides the following important choices:

  • Device (a BJT)
  • Biasing circuit
  • Feedback scheme (Colpitts used in OsCore)
  • Biasing point, which is shown in the OsCore subcircuit (which you can see from the Schematic window by clicking the OsCore component in the design, then pressing the down-arrow from the Main menu). The schematic is shown in the following illustration.

Moreover, the 30 MHz resonance frequency is assumed and the 20-ohm load resistance that models the actual load seen through a buffer amplifier and a matching circuit. At this point, you might want to modify the resonator and the OsCore (or replace them by your own circuit).
The modified circuit can be saved as a new design. We want the S11 trace shown on the polar plot in the data display window to encircle the point 1+j*0 . If this does not happen, the circuit must be modified. In that case, the menu selections Output Load Mapping and Input Load Mapping will help in determining the circuit and the load matching. Refer to the Oscillator DesignGuide Reference for details.

Oscillator Performance

The following menu selections determine the oscillator performance:

  • Fixed Frequency Oscillator
  • Single Frequency Phase Noise
  • Frequency Pulling
  • Frequency Pushing

They determine the oscillation frequency and power, phase and amplitude noise, and circuit elements that contribute most to noise.
You can find frequency variations with load and bias. Modify (or replace) the subcircuits (the resonator, the OsCore, and the load resistance).

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