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CHAPTER 5 - Amplifier Design 220 5.5 Video Tutorials A comprehensive set of videos tutorials on amplifier design is available to the reader. These are essential to the understanding of amplifier design and form the core of the amplifier section. The textbook should just be used for a reference and a brief introduction. VIDEO REFERENCE CONTENT 5.1 BJT Amplifier Design Part 1. I-V characterisation of BJTs. Calculating transistor's beta from IV curves. Passive biasing with feedback. Explanation of feedback mechanism and its usefulness to diminish the effects of temperature induced current fluctuations. Calculation of value of bias resistors, verification of bias through DC current and voltage annotations. Bias adjustments through tuning. DC blocking capacitors to avoid test ports loading bias network. Difference between real and ideal capacitors, high-frequency capacitor model and parasitics. Introduction to RF chokes. 5.2 BJT Amplifier Design Part 2. RF chokes, how to select their value. Measuring RF current flowing back into power supply and bias voltage ripple to work out the appropriate inductor value. Difference between real and ideal components. High frequency model of inductors. Transistor characterisation through two-port S-parameters. 5.3 Amplifier Stability Part 1. Gain Variation versus frequency. Polar representation of S 21 . Explanation of how the phase winds back as frequency increases thereby making input-output interaction more likely and increasing risk of oscillations. Rationale behind stabilisation: attempt to conjugate match input without stabilising and demonstration of resulting output instability. Mu factor: a single parameter as an indicator of potential instability and unconditional stability. Input and output stability circles. Resistive stabilisation with shunt and series resistors at input and/or output and its limitations. 5.4 Amplifier Stability Part 2. Stabilisation though reactive emitter degeneration (small inductor). Demonstration of its validity at frequency of interest and higher frequencies. Analysis of stability at lower frequencies when this technique is used. Demonstration of need for stabilisation at frequencies lower than operating frequency. Design of additional resistive branch rendered inactive with quarter wave transformer at frequency of interest to increase gain. Mu factor versus frequency for reactive stabilisation and purely resistive stabilisation. Comparison of broadband performance and identification of improvements needed in purely resistive stabilisation which result in further loss of gain. Conquer Radio Frequency 220 www.cadence.com/go/awr