# What's wrong with my sine wave generator?

I was given a task to generate a sine wave by using TLC2274ACN. The circuit is as follows. But at the output i'm getting a DC voltage when I measured it in Oscilloscope. I believe that the circuit is pretty much correct as I have gone though several websites but in those websites the opamps are different from what I used in my circuit.

In LTspice simulator, I'm getting a sine wave with these values. If the circuit diagram is right, then why am I receiving DC instead of AC in oscilloscpe?

• That schematic is quite annoying to look at with the ground connection going up like that. – Olin Lathrop Feb 13 '18 at 12:39
• We have no idea what you did in reality, maybe you made a mistake, we can't tell. Also you are running a simulation with ideal components with perfect values. You will not have a 33nF capacitor or a 10k resistor or a 5V voltage source in reality. – PlasmaHH Feb 13 '18 at 12:42
• what's the frequency you're aiming for? Also note that though not "small" by modern electronics standards, 33nF is in the region of stray capacitances that you can incur when working on breadboard (sublime message: BREADBOARD IS EVIL UNLESS YOU KNOW WHAT YOU'RE DOING) – Marcus Müller Feb 13 '18 at 13:15
• Being bored I recreated your circuit and lo and behold, it doesn't oscillate at all here. – PlasmaHH Feb 13 '18 at 13:25
• Iomesh pudipeddi, in case you want to have a tunable oscillator for many frequencies, the WIEN type oscillator is NOT the best solution because you always have to tune TWO parts in parallel (R7 and R8 resp. Ce and C4 at the same time). – LvW Feb 13 '18 at 14:36

For a wien bridge oscillator the gain needs to be 3 to sustain oscillation but, to begin oscillation, it needs to be higher. Your gain is 1 +363/180 = 3.0167 and too close to begin oscillation (especially given that if you used 1% resistors the gain might be only 1.98).

The next problem will be that when you increase the gain to begin oscillation you will find that the sine wave output ramps up in amplitude and clips the op-amp rails. So, you have to use a non-linear gain feature like this: -

The diodes act like open circuits when oscillation begins (maybe R3:R4 is set at 5:1 or thereabouts) and as amplitude increases the diodes start to conduct and shunt that ratio of R3:R4. This of course can lead to unacceptable sinwave distortion so other more complex methods are used that I'll leave with you to research.

Of course, as per what Olin said, I suspect that you are overloading the op-amp with too small values for your R5 and R6 but it might work if you increased your R6 to 470 ohms.

• As you suggested I increased the load resistance value to have a gain (a bit higher than 3 to start oscillate), there's lot of distortion but atleast not DC this time which I would consider as some progress. I watched few videos in internet and notice that they have very good sine wave but when I use it with a different opamp there's lot of distortion. To make sure all my components were working fine, I used new ones but still the problem is same. – lomesh pudipeddi Feb 13 '18 at 16:07
• @lomeshpudipeddi it's difficult to make really good sine wave generators given your starting point. – Andy aka Feb 13 '18 at 16:12
• @lomeshpudipeddi if you are satisfied that this answers your original question then please consider formally accepting it. – Andy aka Feb 21 '18 at 12:38

You didn't provide a link to the opamp datasheet, so this is only a guess.

You are asking the opamp to drive a 543 Ω load to ground. Make sure it can actually do that over the output voltage range you want.

• max output per channel as per mouser product page (couldn't be bothered to read the datasheet myself) is 50 mA; that should suffice, assuming the amplitude isn't larger than 10V or so (which would be impossible with the supply voltage) – Marcus Müller Feb 13 '18 at 13:14
• According to the data sheet, if it's a dual supply, the max voltage should be +/- 8V. Are you saying that my supply voltage would be a problem in this case? – lomesh pudipeddi Feb 13 '18 at 13:46
• No - the max, supply voltages are +- 18 volts. What is the value of the observed DC voltage??? – LvW Feb 13 '18 at 15:40
• The observed DC voltage is around 3.5 V with inputs of +5V and -5V. – lomesh pudipeddi Feb 13 '18 at 15:52