Basic Oscillator Model• Oscillator has positive feedback loop at selected frequency• Barkhausen criteria implies that the multiplication of the transfer functions of open loop amplifier and feedback stage is HF (ω)HA (ω) = 1• Barkhausen criteria aka loop gain equationLC Oscillators – Lower RF FrequenciesLC Oscillators – Lower RF FrequenciesLC Oscillators – Lower RF Frequencies• Can also design with BJTs.High RF & Microwave Oscillators• Take advantage of our knowledge of stability• Rollett Stability Factor k < 1Microwave Oscillator Signal Flowb1/bs=Γin/ (1- ΓsΓin)Conditions of oscillation –Unstable if:ΓsΓin= 1 or ΓsΓL= 1Creating Oscillator Condition• Frequently begin with common-base or common-gate configuration• Convert common-emitter s-parameters to common-base (similarly for FETs)• Add inductor in series with base (or gate) as positive feedback loop network to attain unstable Rollett factor k <1Unstable Condition – Oscillation1. Convert transistor common-base [s] to [Z]tr2. [Z]L= 3. [Z]Osc= [Z]L+[Z]tr4. Convert [Z]Osc to [s]Osc5. Plot stability circles1111jLωInductor Value for Oscillation• Must repeat previous calculation ofRollet Factor for each value of L• In this exampleL = 5 nHs11= -0.935613, s12= -0.002108, s21= 1.678103 , s22= 0.966101Unstable Transistor Oscillator Design1. Select potentially unstable transistor at freq2. Select appropriate transistor configuration3. Draw output stability circle in ΓLplane4. Select appropriate value of ΓLto produce largest possible negative resistance at input of transistor yielding |ΓL| >1 and Zin< 05. Select source tuning impedance Zs as if the circuit was a one-port oscillator by RS+ RIN< 0 typically RS= |RIN|/3, RIN< 0 and XS= -XIN6. Design source tuning and terminating networks with lumped or distributed elementsDielectric Resonator Oscillator (DRO)DRO NetworksDR-based input matching network of the FET oscillator.Varactor Diodes (Voltage Variable Caps)Gunn Elements For OscillatorsGunn Oscillator with DROMixer BasicsHeterodyne receiver system incorporating a mixer.Basic mixer concept: two input frequencies are used to create new frequencies at the output of the system.Mixing Process SpectrumSimple Diode and FET MixersCompression Point and 3rdOrder InterceptSingle-Ended BJT MixerSingle-Ended BJT Mixer Design Biasing NetworkSingle-Ended BJT Mixer DesignLO and RF ConnectionSingle-Ended BJT Mixer DesignRF Input Matching NetworkSingle-Ended BJT Mixer DesignModified Input Matching for RFSingle-Ended BJT Mixer DesignCompleted