single supply op amp oscillator

Thread Starter

kahafeez

Joined Dec 2, 2008
150
hey people can we make a sine wave oscillator using a single supply op amp??? or will the negative half of the wave clip off???
 

KL7AJ

Joined Nov 4, 2008
2,208
Certainly...but you have to use an output coupling capacitor, at the very least. You will also have to forward bias your non-inverting input....a simple voltage splitter does the trick here.

eric
 

gsjaved

Joined May 7, 2009
2
Can the schematic of op amp 741 model be used to design a +Vcc/Gnd op amp.

I tried using it, But the circuit always saturates to the Vcc voltage. The biasing in the circuit, does not come to Vcc/2 (rather I am not able to do it, I started my work by "designing" a single supply op amp).

Any suggetions.
I did go through the materials from TI. But somehow was not convinced.
Regards

Javed
 

Wendy

Joined Mar 24, 2008
21,840
Schematic please? There are ways to use a single supply voltage, but a 741 needs a lot more voltage than most. When you look at the spec sheet they neglect to specify a minimum voltage. I suspect without knowing (because you didn't specify) that you are starving the op amp for power. Figure 12VDC as an absolute minimum, more is better.

A LM324 is speced for down to 3VDC, as are many newer op amps.

Have you read this?

Creating a Virtual Power Supply Ground

BTW, most of the older op amps, which includes the LM324, have crossover distortions. This will screw with a clean sine wave. How do I know this?

http://forum.allaboutcircuits.com/showthread.php?t=12405

Something to be aware of.
 
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gsjaved

Joined May 7, 2009
2
I am actually "designing", rather simulating it on Cadence.

The flow is like this,
R2 = R3 = 3600 Q3 area = 3
R1 = 2.5k voltage at the output = -3.24v
R13 = 28k voltage at he base of Q1,Q7 = -1.25V
R8 = 25 cap = 30pF
R17 = 50
R81 = 200

I request you to tell me the mistakes done in this design under these categories:

1. Blunders
2. never do it
3. silly
4. "foolish"

In this particular design, I have observed that Q3 saturates and pulls the output to +4.668v when Q30 is changed to "pnp" from "npn"

The model files used are from the foundry kit.

My doubts:
Does this need a start up circuit?
Does it need a completely different biasing technique , if I were to implement a similar design for +Vcc(+5v)/Gnd supply ?

Target :
Design an op amp for +5V/ Gnd , Avol = 80dB, BW = 1Mhz.
 

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