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I am constructing 10kHz , 30kHz and 50kHz sine waves using wien bridge oscillator design with LM358 OP-Amp. I have a few problems with the circuits that i could not figure out. Thank you for all your helps.

1)The output sine waves are getting distorted as the frequency increases. It is OK for 10kHz but when i increase the frequency more to 30kHz or to 50kHz I am getting the following distortions on my waves. I have tried changing the Op-Amp, (not the model), changing the source changing the values for resistors but could not fix it. Distortions at 30kHz

2) And secondly I want to amplify the waves but non-inverting amplifier or inverting amplifier with only resistors aren't working. I've read the data sheet of LM-358 there is an example amplifier circuit for AC signals. However I couldn't figure out what component does what. Do I have to use that circuit or is there a simpler solution. Example Amplifier Circuit

Again Thank you for all your kind help.

Dhasvan
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  • From the related questions, definitely try to implement this with ±V rails and use something like in https://electronics.stackexchange.com/questions/78388/what-is-the-function-of-the-bulb-in-a-wien-bridge-oscillator . Find an op-amp with enough GBW and slew rate to have a good output at the desired frequency, then you can have a much higher frequency ceiling. Be careful with very high GBW op-amps, though, they like to have uncontrolled oscillations. – user2943160 May 20 '16 at 05:30
  • What wien bridge circuit did you use? – Andy aka May 20 '16 at 09:03
  • This one: http://i.stack.imgur.com/Idtcq.jpg – Dhasvan May 20 '16 at 12:16

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1) Sorry to be the bearer of bad tidings, but running a 358 at more than about 10 kHz is a losing proposition. The data sheet show figure 7 (page 10) shows maximum voltage swing vs frequency, and you can see that 10 kHz is marginal, and 30 kHz and 50 kHz are worse. Get a faster op amp.

2) You do need all those components, but there is also a "simpler" way to do it. Get a second power supply and drive your circuit with +/- voltage, and your circuits will be greatly simplified.

WhatRoughBeast
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  • Thank you for your response. Which Op-Amp do you suggest? For example do you think LM741 would be sufficent? I am using 2 supplies +12V and -12V. – Dhasvan May 19 '16 at 22:19
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    A 741 is even worse. Am I correct in thinking you need a DIP package? – WhatRoughBeast May 19 '16 at 23:02
  • Yes i need DIP package :) – Dhasvan May 19 '16 at 23:06
  • If you read here http://electronics.stackexchange.com/help/on-topic you'll see that shopping recommendations are not kosher here, but I'll give you some guidelines. Go to one of the on-line electronics distributors (Digikey, Mouser, Newark, Allied, etc) and call up a product selection page for op amps. You'll need to look for voltage supply 36 volts, gain-bandwidth product at least 3 MHz (and 10 times better won't hurt), and slew rate of 6-7 V/usec or better. And DIP package, of course. If you're really uncertain, come back with your best choice and open a question about its appropriateness. – WhatRoughBeast May 20 '16 at 00:59
  • An LF353 8 pin dip has a 13V/uS slew rate and a gain bandwidth product of 4 MHZ, but you will need a bipolar power supply of +/- 12 to +/- 15 volts. –  May 20 '16 at 00:59
  • Also, you should be aware that 50 kHz is right at the upper limit of what Wein bridges are used for. – WhatRoughBeast May 20 '16 at 01:04
  • @WhatRoughBeast with a high speed, modern op amp, that is very much not the case: http://www.jensign.com/wien/ (1MHz) – user2943160 May 20 '16 at 05:22
  • Thank you all for comments I will try and to all the things you suggested – Dhasvan May 20 '16 at 12:15
  • @user2943160 - I didn't say it can't be done, just that it usually isn't. Among other things, lamp-stabilized Wein bridge oscillators tend to environmental temperature effects. – WhatRoughBeast May 20 '16 at 12:41
  • @WhatRoughBeast that's where it's great to injection-lock the oscillator as a (sub) harmonic of some driving signal. https://cds.linear.com/docs/en/article/injection-lock_a_wien-bridge_oscillator.pdf – user2943160 May 21 '16 at 00:06