Rendering demonstration of function signal generator based on op amp design_Basic hardware circuit diagram explanation

Circuit diagram:

Circuit function:

This circuit example uses the LM324 operational amplifier to design a function signal generator for square waves, triangle waves, and sine waves.

Circuit breakdown:

The module division of the entire circuit is obvious, and its structure is as follows:

One is a hysteresis comparator composed of U1A, peripheral resistors and voltage regulator tubes, which generates a square wave signal;

The second is an integrating circuit composed of U1B, which generates a triangular wave signal;

The third is a first-order low-pass active filter composed of U1C and peripheral resistors and capacitors to generate a sine wave.

The working process of the entire circuit is as follows:

In the circuit, the square wave generator and the triangle wave generator are connected end to end, forming a positive feedback closed-loop system. The square wave output by the comparator U1A is output by the integrator U1B to obtain a triangular wave, and the triangular wave triggers the comparator to automatically flip to form a square wave, thus forming a triangular wave and square wave generator. At the same time, in this example circuit, an integrating circuit composed of an operational amplifier is used, so constant current charging can be achieved, greatly improving the linearity of the triangle wave.

In more popular terms, when the comparator output causes the non-inverting terminal voltage of the comparator to be higher than 0V, the output of comparator U1A flips to high level, that is, Uz+0.7V; when the comparator output causes the non-inverting terminal voltage of the comparator to rise When the voltage is lower than 0V, the output of comparator U1A flips to low level, that is - (Uz+0.7V).

In this way, when the comparator outputs high level, the triangular wave output changes in the negative direction; when the comparator output is low level, the triangular wave output changes in the positive direction.

By repeating this continuously, triangle waves and square waves are obtained.

The amplitude of the square wave is limited by the voltage regulator tube; while the amplitude of the triangular wave is R8*Uz/R5. How this is obtained can be calculated based on the virtual short and virtual break principles of the op amp.

The principle of sine wave output is as follows:

It can be seen from the expansion of the triangular wave into a Fourier series that it contains the fundamental wave and odd harmonics such as the 3rd and 5th order. Therefore, the triangular wave can be converted into a sine wave by taking out the fundamental wave and filtering out the higher harmonics through a low-pass filter.

However, the passband cutoff frequency of the low-pass filter should be greater than the fundamental frequency of the triangular wave and less than the third harmonic frequency of the triangular wave.

U1C in the picture is a common inverting input first-order low-pass filter. In fact, it is an integrating circuit. Its analysis method is similar to that of a first-order integrating circuit, but it is different from the integrating circuit. The following is an analysis of the two found on the Internet for your reference:

Some literature confuses integrators with RC low-pass filters, but they are not the same.

From the transfer function:

The transfer function of the integrator is: Vout/Vin=ω0/s, and the transfer function of the first-order RC low-pass filter is: Vout/Vin=ω0/(s+ω0).

It can be seen that when the signal frequency is much higher than the corresponding frequency of ω0, the characteristics of the two are equivalent. That is to say, in terms of high-frequency attenuation characteristics, the two are very similar.

However, there is an essential difference between the two in terms of low-frequency "low-pass" characteristics. When the signal frequency is lower than the corresponding frequency of ω0, especially when the signal is DC, the low-pass filter output is equal to the input, while the integrator output changes with time. , will rise to the upper limit of the voltage allowed by the circuit (the ideal integrator will reach infinity).
It should be said that the high-frequency characteristics of the integrator and the low-pass filter are basically the same, but the low-frequency characteristics are essentially different.

Notice:

To better understand the circuit in this example, you should start with mathematical calculations, analyze how different output functions are affected, and then adjust some parameters of the resulting waveform, such as frequency, amplitude, phase, etc., based on these analyses.

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Circuit diagram:

Circuit function:

By adjusting the adjustable resistor R1, the duty cycle of the output rectangular wave is changed.

The working process of the entire circuit:

The entire circuit structure is a hysteresis comparator composed of an op amp. By adding diodes D1 and D2, it becomes a square wave generator with adjustable output duty cycle.

The unidirectional conductivity of the diode is used here to make the charging and discharging circuits of capacitor C1 different, thus changing the duty cycle of the output square wave.

When capacitor C1 is charging, its circuit is the lower half of adjustable resistor R1, diode D2, and resistor R2.

When capacitor C1 discharges, its circuit is resistor R2, diode D1, and the upper half of adjustable resistor R1.

Therefore, by adjusting R1, the charging constant and discharging constant of capacitor C1 are changed. In this way, the duty cycle also changes.

As for why this circuit outputs a square wave, you can search it on Baidu: Op Amp Hysteresis Comparator Square Wave Generator. You can find it, this is a very basic circuit.

Notice:

This example circuit does not take into account the output waveform frequency!

-The Electronic Components Purchasing Network (www, oneyac, com) is a local component catalog distributor. It adopts the "small batch, spot, sample" sales model and is committed to meeting customers' procurement needs for multiple models, high quality, and fast delivery. Self-built and efficient intelligent warehousing, with over 50,000 self-operated inventories, provides one-stop genuine spot procurement, personalized solutions, option substitution and other diversified services. (This article is compiled from the Internet for the purpose of disseminating useful information and knowledge. If there is any infringement, please contact the administrator to delete it)