Wen's Oscillation Problem

S3S4S5S6

Wen's Oscillation Problem [Copy link]

 

Is the current-type op amp or the voltage-type op amp used for the Wen oscillation? The relevant information only talks about the peripheral parameters, and there is not much introduction about the op amp itself.

maychang

"Should a current-type op amp or a voltage-type op amp be used for Wien oscillator?" A voltage-type op amp should be used.

S3S4S5S6

maychang posted on 2019-4-29 11:17 "Should a current-mode op amp or a voltage-mode op amp be used for the Wen oscillator?" A voltage-mode op amp should be used.

Can't a current-mode op amp be used?

maychang

S3S4S5S6 Published on 2019-4-29 11:19 Can't current-mode op amps be used?

"Can't current-mode op amps be used?" It's not that they absolutely can't be used, but current-mode op amps are not suitable for use in this situation.

S3S4S5S6

maychang posted on 2019-4-29 12:07 "Can't the current-type op amp be used?" It's not that it can't be used, but the current-type op amp is not suitable for this occasion.

Another question, I want to use OPA690, use positive and negative 5V power supply, and use the Wien bridge to build a sine wave oscillation circuit. The SR of 690 is 1800V/us, and the bandwidth is 500M (G=1). If the circuit is built, can the sine wave oscillation frequency reach 5Mhz? (Attached is the 690 manual)

maychang

S3S4S5S6 Published on 2019-5-6 10:52 Another question, I want to use OPA690, use positive and negative 5V power supply, and use Wien bridge to build a sine wave oscillation circuit. The SR of 690 is 1800V/us, ...

According to the datasheet, it should be possible. But the 5MHz frequency is relatively high, so the component distribution parameters must be paid attention to, and the wiring should also be cautious.

star_66666

Let's take a look at the information first

The circuit diagram of the Wen bridge oscillator is as follows:

From the circuit structure, the circuit is composed of two "bridge arms", R1 and RF form the negative feedback bridge arm, and the parallel RC network and the series RC network are connected in series to form the positive feedback bridge arm. In other words, the Wen bridge oscillator has both positive feedback and negative feedback. When the frequency is infinitely low, that is, when f approaches 0, f0/f approaches infinity, and the total gain approaches zero. When the frequency is infinitely high, that is, when f approaches ∞, f/f0 approaches infinity, and the total gain approaches zero.

S3S4S5S6

maychang posted on 2019-5-6 11:01 According to the datasheet, it should be possible. But the 5MHz frequency is relatively high, so the component distribution parameters must be paid attention to, and the wiring should also be cautious.

Through simulation, the waveform generated by this method will have clipping distortion, and there will still be a little bit after adding the amplitude stabilization circuit. How to further overcome the clipping distortion?

maychang

S3S4S5S6 Published on 2019-5-6 20:12 Through simulation, the waveform generated by this method will have clipping distortion, and it will still exist a little after adding the amplitude stabilization circuit. How to further overcome the clipping distortion

The waveform generated by this method will have clipping distortion, and it will still exist a little after adding the amplitude stabilization circuit. How to further overcome the clipping distortion There are many types of amplitude stabilization circuits for Wien bridge oscillator circuits. Which amplitude stabilization circuit do you use? It is best to post the diagram and indicate the component values.

S3S4S5S6

maychang posted on 2019-5-6 20:16 The waveform generated by this method will have clipping distortion, and it will still exist a little after adding the amplitude stabilization circuit. How to further overcome the clipping distortion Wien bridge oscillator...

The figure is the simplest form of reference on the Internet

maychang

This is a circuit that uses the nonlinearity of the diode forward voltage-current to stabilize the amplitude. I have posted three posts about sine wave oscillation circuits. The first post Miscellaneous Talks on Sine Oscillation Circuits (Part 1) talked about this circuit, which you can refer to.

maychang

S3S4S5S6 posted on 2019-5-6 21:46 The graph is the simplest form on the Internet

The principle of minimizing the nonlinearity of the diode is to reduce the nonlinearity of the diode. In this post, a resistor is connected in parallel with two anti-parallel diodes, which obviously reduces the nonlinearity of the diode. If you want to further reduce the nonlinearity of the diode, then connect a small resistor in series with each diode. The principle is that when the oscillation amplitude does not make the diode conduct, the loop gain is slightly greater than 1, and the gain is reduced to 1 when the amplitude reaches a certain value. Of course, the cost of connecting resistors in series to reduce the nonlinearity of the diode is slow oscillation, and it takes a relatively long time for the oscillation amplitude to reach stability.

S3S4S5S6

maychang posted on 2019-5-7 07:43 The principle of minimizing the nonlinear effect of diodes is to reduce the nonlinearity of diodes. This post uses a resistor and two anti-parallel diodes...

Another point is that when the oscillation is at low frequency, the potential parasitic parameters of the circuit can be ignored, but when the frequency reaches megahertz, I am worried that the diodes and various parasitic parameters will cause further distortion of the waveform.

maychang

S3S4S5S6 Published on 2019-5-7 11:10 Another point is that when the oscillation is at low frequency, the potential parasitic parameters of the circuit can be ignored, but when the frequency reaches megahertz, I am worried about the diode...

The oscillation frequency is as high as several MHz, of course, the influence of distributed parameters is more serious. This can only be discovered after the actual circuit is built. It is difficult to simulate the influence of distributed parameters. Obviously, the simulation software does not know what the distributed parameters of your circuit are.

captzs

S3S4S5S6 Published on 2019-5-7 11:10 Another point is that when the oscillation is at low frequency, the potential parasitic parameters of the circuit can be ignored, but when the frequency reaches megahertz, I am worried about the diode...

It is not suitable to use Wien oscillation at high frequency.

gmchen

S3S4S5S6 Published on 2019-5-7 11:10 Another point is that when the oscillation is at a low frequency, the potential parasitic parameters of the circuit can be ignored, but when the frequency reaches megahertz, I am worried about the diode...

1. Using field effect tubes to limit the output can make the output distortion relatively small. 2. If it is only one or two megahertz, the impact of parasitic parameters is not the most serious.

captzs

If clipping occurs, use an op amp with a smaller slew rate or a smaller GBW, and the output amplitude will be small and there will be no clipping.

S3S4S5S6

captzs posted on 2019-5-7 11:30 It is not suitable to use Wien oscillation for high frequency.

Is there any good solution (to be done with pure hardware) to generate sine waves with a large frequency span, adjustable from a few hundred hertz to megahertz, and low waveform distortion?

zhuyebb

I'm just passing by, hehe

maychang

S3S4S5S6 Published on 2019-5-7 11:54 Is there any good solution (to be done with pure hardware) to generate a sine wave with a large frequency span, adjustable from a few hundred Hz to over MHz, and with low waveform distortion...

The frequency span is adjustable from a few hundred Hz to over MHz, and the waveform distortion is required to be small. The Wien bridge is the most appropriate.