Wideband/HF Amplifier Design Techniques

Course 202

Summary:

Wideband amplifiers typically have bandwidths of DC to multi-GHz while maintaining a good step response (MFED). This course uses simplified models to develop the theory needed to understand and develop such circuits. The student will learn not only the theory and practice of wideband amplifier design, but will also learn techniques that provide a “gut level feel” for designing almost any analog circuit. Using these techniques, the student will learn how to derive equivalent circuits, some containing negative elements that describe for example, why oscillations occur. Once the basic theory is developed, a variety of additional simulation tools are brought in to complete the last 10% of the design and provide verification of the efficacy of the simplified algebraic models.

Learning Objectives:

Upon completing the course, the participant will be able to:

Design wideband amplifiers
Have an understanding of the use of simplified models applicable to any high frequency design
Identify the structures and mechanisms that cause aberrant circuit behavior such as circuit oscillations and what to do to fix these circuits
Have knowledge of certain very useful rules of thumb
Understand filter theory and the concept of Maximally Flat Envelope Delay (MFED) filters that create maximum bandwidth with low overshoot in the time domain.
Understand peaking networks such as the T-Coil that converts a capacitive load into a purely resistive load suitable for transmission line termination while providing an MFED step response and a bandwidth improvement factor of 2.72
Understand how RF simulation tools such as Smith Charts are extremely useful for time domain analysis while also showing how time domain tools such as SPICE and step response can be quite useful for RF designs.

Target Audience:

Engineers who need a deeper understanding of high frequency and/or wideband amplifier design will benefit from this class. The techniques, methodology, and actual circuits are directly applicable to virtually any analog design.

Familiarity with analog electronics and circuits, Laplace Transforms, and working in the frequency domain is strongly recommended.

Outline:

Day One

Basic Filter Theory: MFED, Butterworth, and Elliptic Filters, Phase Delay and Envelope Delay, Risetime, Overshoot, Bandwidth
• Rules of Thumb: Risetime Bandwidth Product, Cascaded Risetime, Bandwidth Shrinkage Factor, Optimum Number of Cascaded Stages • Peaking Circuits: Series Peaked, Shunt Peaked, T-Coil Peaked • Advanced Passive Circuits: Unbalanced T-Coils, Use of T-coils in Unusual Applications, Transmission Line Termination using T-Coils

Day Two

Basic Models
• Develop Simplified High Frequency Transistor (BJT and FET) Models: Frequency Dependent Current Sources • Use Models: Predict Input Impedance to Amplifier, Negative Element Creation, Oscillations, Negative Element Cancellation • Input and Output Circuit Impedances • Creating Ideal Amplifier Input Impedance • Combine with Peaking Circuits to Get Maximum Bandwidth • Using CAD software to Fine Tune the results • Stability Analysis: Stability Circles, Routh-Hurtiz • Create Equivalent Networks: Cauer Series Expansion • Package Parasitics’

Day Three

Difference Amplifiers
• Creating a Basic Gain Stage Using a Difference Amplifier • Single Ended and Double Ended Drive • Level Shifting Circuits • High Frequency Analysis of Difference Amplifier: Stability, Step Response • Available Gain from a Difference Amplifier • Input Impedance of Difference Amplifier: Making it Look Purely Capacitive • Apply Peaking Circuits to Difference Amplifier for Maximum Bandwidth • Ft Doubler Circuits • Noise Figure • Output Impedance of Difference Amplifier • Driving a Capacitive Load: Spiking Networks • Cascade Difference Amplifiers for Maximum Gain-Bandwidth Product • Designing highly linear amplifiers using feed forward techniques

Subject Areas Covered

RF Power Amplifier Design

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