{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

ass5_f2011

# ass5_f2011 - ECE 100 Lab 5 Design of an Oscillator Winter...

This preview shows pages 1–2. Sign up to view the full content.

ECE 100 Lab 5 Design of an Oscillator Winter 2011 We have given a good deal of thought to preventing circuits from oscillating, but, of course, there are times when you want the circuit to oscillate. Such a circuit is the “Wien-Bridge Oscillator”. It has been a popular oscillator in the audio frequency range and is of historical interest because it was the first product developed and sold by the Hewlett-Packard company. The basic oscillator is sketched to the right. It is based on an amplifier with a voltage gain K = 3, here shown implemented as a follower with gain. The feedback is through the RC network shown where the two R’s and the two C’s are the same. 1. System Level Design: Show that the feedback factor B(s) = sRC/(1 + 3sRC + (sRC) 2 ). The loop gain will be T(s) = -K B(s) because the feedback is to the positive input terminal. For this circuit the Nyquist plot is quite useful. You can do it with Matlab as follows: >> s=tf('s'); >> tau = 1e-4; >> t = -3*s*tau/(1+3*s*tau+(s*tau)^2); >> nyquist(t) You will see a beautiful circular trace that goes right through the –1 point twice, meaning there are two poles on the ω axis. If K > 3 the poles are in the RHP and if K < 3 they are in the LHP. The resonant frequency is ω 0 = 1/RC. To make a real oscillator we need K a bit greater than 3 so the oscillator will start up, but when it reaches

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 2

ass5_f2011 - ECE 100 Lab 5 Design of an Oscillator Winter...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online