oscillator - eem.eskisehir.edu.treem.eskisehir.edu.tr/cozzaim/EEM 509/icerik/example9.pdf · 1-...

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1- S-parametreleri ( 0 ( 50 ) Z = ) ve devresi aşağıda verilen transistor ile 6 GHz osilator tasarlanacaktır. Bu osilator için 0.9 130 L Γ = ° ise girişteki direnç değeri ve iletim hattı uzunluklarını hesaplayın 1- Design a transistor oscillator at 6 GHz using a FET in a common source configuration driving a 50 ohm load on the drain side. The S-parameters are 0 ( 50 ) Z = : 11 0.9 150 S = ∠− ° , 21 2.6 50 S = ° , 12 0.2 15 S = ∠− ° , 22 0.5 105 S = ∠− ° . a) Calculate and plot the output stability circle, and choose T Γ for 1 in Γ . b) Design load and terminating networks as below. Attach your Smith Chart. choose is large by trial and error 11 11 12 21 2 2 2 2 22 22 12 21 11 22 ( ) 8.09 15 , 8.28 , 1& . 1 0.9 130 1.61 162 12 7.5 3 4 7.5 . T T L in L in L L in in G in S S SS C R S S SS S S Z j Z R j −∆ = = ∠− ° = = −∆ −∆ Γ Γ = + Γ < Γ Γ ⇒Γ = °⇒Γ = ∠− °⇒ =− Ω⇒ = = +

Transcript of oscillator - eem.eskisehir.edu.treem.eskisehir.edu.tr/cozzaim/EEM 509/icerik/example9.pdf · 1-...

1- S-parametreleri ( 0( 50 )Z = Ω ) ve devresi aşağıda verilen transistor ile 6 GHz osilator

tasarlanacaktır. Bu osilator için 0.9 130LΓ = ∠ ° ise girişteki direnç değeri ve iletim hattı uzunluklarını hesaplayın 1- Design a transistor oscillator at 6 GHz using a FET in a common source configuration driving a 50 ohm load on the drain side. The S-parameters are 0( 50 )Z = Ω :

11 0.9 150S = ∠− ° , 21 2.6 50S = ∠ ° , 12 0.2 15S = ∠− ° , 22 0.5 105S = ∠− ° . a) Calculate and plot the output stability circle, and choose TΓ for 1inΓ ≫ . b) Design load and terminating networks as below. Attach your Smith Chart.

choose is large by trial and error

11 11 12 212 22 2

22 22

12 2111

22

( )8.09 15 , 8.28

, 1& .1

0.9 130 1.61 162 12 7.5 3 4 7.5 .

T T

Lin L in

L

L in in G in

S S S SC R

S S

S SS

S

Z j Z R j

∗ ∗−∆

= = ∠− ° = =− ∆ − ∆

ΓΓ = + Γ < Γ

− Γ

⇒ Γ = ∠ ° ⇒ Γ = ∠− ° ⇒ = − − Ω⇒ = = + Ω

1- Find the voltage gain of a feedback network from the amplifier output to the input such that the circuit will oscillate at a frequency of 1 GHz. The voltage gain of an amplifier is

9

2 30( )

1 (2 10 )A ω

ω π∠ °=

+ ×

2- The gain-phase method of oscillator analysis is particularly useful because it offers a way to directly compare simulations and measurement. Explain.

9- Consider the Op Amp relaxation oscillator shown in figure below. Suppose that the capacitor has a value of 1 nF and that the resistance, Rc, is equal to 20 K. Let R1=R2= 50 K.

a) What is the output frequency of this oscillator?

b) Draw the waveforms at Vc and Vout. Give the amplitude of each waveform.

2- Consider the following circuit, where 30(1 )inR A= − − Ω . Find the frequency of oscillation

and the value of RL that maximizes the delivered power.

4- Consider the op amp Colpitts oscillator shown below. Let the transconductance of the amplifier be 0.05 A/V, C2=50C1, and L=200 µH.

5- For the oscillator shown below R1=10 kΩ, R2=5 kΩ, Re=8.6 kΩ, L=2 mH, C1=1.27 nF, C2=0.127 µF, Cb=Cc=10 µF, Vcc=15 V.

a) What is the name of this oscillator? Colpitts b) Find the resonant frequency.

1 2

1 2 3

1100KHz

2

C Cf

C C Lπ

+= =

c) This circuit will oscillate at a frequency of 100 kHz if the correct value of RL is used. Determine RL. (Hint: Find gm from DC analysis of the transistor.)

6- Consider the relaxation oscillator shown below

1- Consider the negative resistance oscillator shown in Figure 1. Suppose that RL = 100 ohm, RC = 4.65 K, L = 100 µH. The oscillation frequency is to be 600 kHz. Determine the capacitances, C1 and C2, required to make this circuit oscillate at the desired frequency.

3- Design the Colpitts oscillator depicted below to oscillate at a frequency of 100 MHz. The circuit should deliver 20 mW of power to the 3 kΩ load. The inductor has a value of 25 nH and parallel parasitic resistance of 8 kΩ. Let Re=45 Ω and Re2=600 Ω. Determine the value of capacitors C2 and Cf and the required supply voltage Vcc.

3- Design the Colpitts oscillator depicted below to oscillate at a frequency of 800 MHz. The circuit should deliver 5 mW of power to the 1.2 kΩ load. The inductor has a value of 4.5 nH and parallel parasitic resistance of 7 kΩ. Let C1 = 6 pF, Re=51 Ω and Re2=750 Ω. Determine the value of capacitors C2 and Cf and the required supply voltage Vcc.

3- Figure below illustrates an oscillator circuit minus the DC bias. Assume the DC collector current is 1.3 mA.

a) What type of oscillator does this circuit represent? Hartley b) Determine the forward gain Av of the oscillator.

c) Determine the feedback gain B.

d) Explain why this circuit will not oscillate in steay state.

e) Can it be made to oscillate by changing the load resistance RL?

4- Discuss how the frequency of a crystal oscillator varies with temperature. Discuss methods that can be utilized to stabilize the frequency of a crystal oscillator against variations in temperature.

5- Given the Colpitts crystal oscillator shown below. How would you modify this crystal oscillator to produce an output frequency of 32 MHz without changing the frequency of the crystal? Explain and draw the appropriate circuit diagram.

6- An RF amplifier has 21 4.5 10S = ∠ − ° , 11 0.25 180S = ∠ ° and 22 0.5 0S = ∠ ° . (1) Design a

PI-network that will cause oscillation at a frequency of 150 MHz. Give a circuit of your network with all elements carefully labeled. (2) Assuming that the components of your network have infinite unloaded Q, determine the loaded Q of your oscillator. Make reasonable assumptions.

7- The negative conductance generator produces a negative conductance (in mS) given in terms of the peak resonator voltage Vc, by 2

IN 5 8( 1V)CG V= − + .

a) What is the frequency of oscillation in MHz?

b) What is the value of the steady-state peak voltage?

c) What will be the steady-state peak amplitude of the current in the 50 pF capacitor.

d) While testing an oscillator in the laboratory you observe that the output waveform is a very distorted sine wave. What might be wrong with the oscillator? Explain in detail.

8- Explain how this oscillator works. Derive the value of R needed to just start oscillations. What is the oscillation frequency? Use the simplest MOSFET small signal model.

2- Given that 11 1.1 0.06S = ∠ (450 MHz) and 11 1.11 0.07S = ∠ (500 MHz). Design a parallel-resonant negative resistance oscillator that tunes from 450 to 500 MHz. Power is to be extracted from the resonator. The resonator is to be tuned by a single variable capacitor. Give the capacitance values needed to tune the oscillator to 450 and to 500 MHz. Also specify the resonator inductance and the resonator load resistance RR. The resonator should have an external Q of 10. Do not include the transistor negative resistance in the Q-determination. Assume that all components have infinite unloaded Q. Draw a complete schematic of your resonator with all components carefully labeled.