# sine-wave oscillators

Discussion in 'Homework Help' started by zdzislavv, Sep 14, 2009.

1. ### zdzislavv Thread Starter Member

Jun 5, 2009
22
0
Hello!

2. What will happen if for the working oscillator with 3-stage CR phase shifter the shifter is replaced with the 4-stage one (explain why) - the same question for RC, LR or RC phase shifters).
Oscillator will still work, however in different (higher) frequencies. It happens due to phase shift of signal. Both gives 180 + 2pi*r (r=0,1,2,...), for 3 stage shift is 60 degrees, while by 4 stage 45 degrees. We also should mention that if phase shift decreases, frequency increases.

4. Can a 2-stage (3 stage, 4 stage) CR (Rc, RL, CR) phase shifter be used to make oscillator with inverting (noninverting) amplifier (explain why).
2-stage normally won't work (in every case because of wrong phase-shift). Higher stages -> by changing the amplifier, output (from amplifier) wave will have different phase, and it will mismatch the condition of oscillation (cond. of phase).

Source of above questions: http://images47.fotosik.pl/198/6bdc42f9042ca5d6.jpg

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The other thing which I need to do is to solve the following exercise: http://images45.fotosik.pl/199/0e4afa996a5462db.jpg. Can you give me any suggestions?

I guess I need to read two values from those two graphs, e.g. |B(jphi)\=1/2 for f=3kHz and phiB=1/(2pi) for the same frequency.

Then I need to put these values to some formulas. I know two conditions: condition of gain |KB|=1 and condition of phase phi_k + phi+B = 0 or 2k*pi. How to use these formulas for the above values?

Greetings!