dielectric resonator oscillator smith chart

Dielectric resonator oscillator smith chart series#

Then substitute for Zp, we have g m Rp ( jw ) Vout ( jw ) H  jw    Vin ( jw ) 1  jQp  g m Rp ( jw )Īnd the gain condition (Barkhausen) for oscillation is gmRp=1 Thus, any changes will result NCR Limit (cont) The transfer function of the oscillator is given by g m Z p ( jw ) Vout ( jw ) H  jw    Vin ( jw ) 1  g m Z p ( jw ) Parallel impedances for Rp, Lp, and Cp can be written as Z p  jw   Noises cause frequency instability in oscillator. Phase noise-may be due to variation of device capacitance with variation of voltage.This is usually happened in amplifier.Amplitude noise may be converted to phase noise if the amplifier is present. Network at resonator Resonator should be placed at zero or 180o of phase from the transistor. Choose a point in Inside the instability areaĬontinue Calculate the out and in = L using this formula Determine the required coupling coefficient for dielectric resonator and matching.

Dielectric resonator oscillator smith chart series#

Q can be determined by simple measurement of reflection coefficientĮxample (dielectric resonator osc.) Design 2.4GHz dielectric resonator oscillator using series feedback with bipolar transistor having S-parameters (Zo=50ohm) S11= 1.8 / 130o, S12= 0.4 / 45o, S21= 3.8 /36o, S22= 0.7 / -63o. Ratio of unloaded to external Q is given by where R / wo L Q N 2R g   RL=2Zo for loaded resistance 2 Qe RL / N wo L 2Z o = Zo for /4 transmission lineĬontinue (Dielectric resonator) Reflection coefficient looking on terminated microstrip feedline towards resonator is given byĢ 2  N R  Z N R g o o   2 2  N R  Z 2 Z  N R 1 g o o o Where N =coupling factor/turn ratio Q=R/woL (unloaded resonator) Obtain the susceptance and 0.319 distance towards open circuit.ĭielectric resonator Dielectric resonator That the distant between transistor and the stub. Moving towards load until meet the crossing point between SWR circle and the unity circle. The steady -state oscillation frequency will differ from 4Ghz due to the nonlinearity of the transistor 0.241 įor T matching, we can use open-stub to match 50 ohm. Using Rin/3 should ensure enough instability for the startup of oscillator. Using a transmission line to match a resistive load, thus we have a length of 0.241  and a load of 89.5 . T can be choose anywhere in the Smith chart but the main objective in should be larger than 1. Choose RL such that RL+Rin 1, thus the stable region is inside the shaded circle. Draw output stable circle and choose T for large negative resistance (I.e Zin).Typically, common source or common gate are used.Often positive feedback to enhance instability. Choose high degree of unstable device.Design a load matching network for one-port of 50 ohm load oscillator.īy plotting ZL in Smith chart then match to 50 ohm as 50 usual. A negative -resistive diode having Gin=1.25 /40o (Zo=50ohm) at its desired operating point, for 6 GHz. RL / I  X L / I  RL / w  0 By substituting ZT=Zin + ZL, the stability equation reduces to Rin   X L  X in  X in Rin  0 I w I w Stability of oscillation Oscillation takes place when the circuit first unstable, i.e Rin +RL 0 so that  Z T Z T *  RT X T X T RT  0 Or subst Z =R +jX Im  0  T T T I w I w  I w  Z L  Z o  Z in  Z o Zin  Z o 1    Z L  Z o  Z in  Z o Z in  Z o in Oscillation occurred whence ZL= -Zinwhich implies L  Negative resistance device is usually a biased diode. One-port negative Oscillator using IMPATT or Gunn diodes I XL & Electron Eng Engineering Campus USM Nibong Tebal 14300 SPS Penang Microwave Oscillator By Professor Syed Idris Syed Hassan Sch of Elect.