0
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ From the related questions, definitely try to implement this with ±V rails and use something like in electronics.stackexchange.com/questions/78388/… . 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. \$\endgroup\$ – user2943160 May 20 '16 at 5:30
  • \$\begingroup\$ What wien bridge circuit did you use? \$\endgroup\$ – Andy aka May 20 '16 at 9:03
  • \$\begingroup\$ This one: i.stack.imgur.com/Idtcq.jpg \$\endgroup\$ – Dhasvan May 20 '16 at 12:16
2
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ 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. \$\endgroup\$ – Dhasvan May 19 '16 at 22:19
  • 1
    \$\begingroup\$ A 741 is even worse. Am I correct in thinking you need a DIP package? \$\endgroup\$ – WhatRoughBeast May 19 '16 at 23:02
  • \$\begingroup\$ Yes i need DIP package :) \$\endgroup\$ – Dhasvan May 19 '16 at 23:06
  • \$\begingroup\$ If you read here 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. \$\endgroup\$ – WhatRoughBeast May 20 '16 at 0:59
  • \$\begingroup\$ 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. \$\endgroup\$ – Sparky256 May 20 '16 at 0:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.