There is equipment and devices that are not only powered by the mains, but also in which the mains serves as a source of such impulses necessary for the operation of the device circuit. When such devices are powered from the mains with a different frequency or from an autonomous source, a problem arises with where to get the clock frequency from.

The clock frequency in such devices is usually either equal to the mains frequency (60 or 50 Hz) or equal to twice the mains frequency when the clock source in the device circuit is a bridge rectifier circuit without a smoothing capacitor.

Below are four circuits of 50 Hz, 60 Hz, 100 Hz and 120 Hz frequency pulse generators based on the CD4060B chip and a 32768 Hz clock quartz resonator.

Generator circuit at 50 Hz

Rice. 1. Schematic diagram of a signal generator with a frequency of 50 Hz.

Figure 1 shows a 50 Hz frequency generator circuit. The frequency is stabilized by a Q1 quartz resonator at 32768 Hz, from its output inside the D1 chip, the pulses are sent to a binary counter. The frequency division factor is set by diodes VD1-VD3 and resistor R1, which reset the counter every time its state reaches 656. At the same time, 32768 / 656 = 49.9512195.

It's not quite 50Hz, but very close. In addition, by selecting the capacitances of capacitors C1 and C2, you can slightly change the frequency of the crystal oscillator and get a result closer to 50 Hz.

Generator circuit at 60 Hz

Figure 2 shows a 60 Hz frequency generator circuit. The frequency is stabilized by a Q1 quartz resonator at 32768 Hz, from its output inside the D1 chip, the pulses are sent to a binary counter.

Rice. 2. Schematic diagram of a signal generator with a frequency of 60 Hz.

The frequency division factor is set by diodes VD1-VD2 and resistor R1, which reset the counter every time its state reaches 544. At the same time, 32768 / 544 = 60.2352941. It's not exactly 60Hz, but close.

In addition, by selecting the capacitances of capacitors C1 and C2, you can slightly change the frequency of the crystal oscillator and get a result closer to 60 Hz.

Generator circuit at 100 Hz

Figure 3 shows a 100 Hz frequency generator circuit. The frequency is stabilized by a Q1 quartz resonator at 32768 Hz, from its output inside the D1 chip, the pulses are sent to a binary counter. The frequency division factor is set by diodes VD1-VD3 and resistor R1, which reset the counter every time its state reaches 328. At the same time, 32768 / 328 = 99.902439.

Rice. 3. Schematic diagram of a signal generator with a frequency of 100 Hz.

It's not exactly 100Hz, but close. In addition, by selecting the capacitances of capacitors C1 and C2, you can slightly change the frequency of the crystal oscillator and get a result closer to 100 Hz.

Generator at 120 Hz

Figure 4 shows a diagram of a 120 Hz frequency generator. The frequency is stabilized by a Q1 quartz resonator at 32768 Hz, from its output inside the D1 chip, the pulses are sent to a binary counter. The frequency division factor is set by diodes VD1-VD2 and resistor R1, which reset the counter every time its state reaches 272. At the same time, 32768 / 272 = 120.470588.

It's not exactly 120Hz, but close. In addition, by selecting the capacitances of capacitors C1 and C2, you can slightly change the frequency of the crystal oscillator and get a result closer to 120 Hz.

Rice. 4. Schematic diagram of a signal generator with a frequency of 120 Hz.

The power supply voltage can be from 3 to 15V, depending on the supply voltage of the circuit, or rather, on the required value of the logic level. The output pulses in all circuits are asymmetric, this must be taken into account in their specific application.

One minute pulse shaper

Figure 5 shows a circuit for a pulse shaper with a period of one minute, for example, for an electronic digital clock. The input receives a signal with a frequency of 50 Hz from the mains through a transformer, voltage divider or optocoupler, or from another source of frequency 50 Hz.

Resistors R1 and R2, together with the inverters of the D1 chip, designed for the clock generator circuit, form a Schmitt trigger, so you don’t have to worry about the shape of the input signal, it can be a sinusoid.

Fig.5. Pulse shaper circuit with a period of one minute.

With diodes VD1-VD7, the counter division ratio is limited to 2048 + 512 + 256 + 128 + 32 + 16 + 8 = 3000, which, at an input frequency of 50 Hz at pin 1 of the microcircuit, gives pulses with a period of one minute.

Additionally, you can take pulses with a frequency of 0.781 Hz from pin 4, for example, to set the hour and minute counters to the current time. The voltage of the power supply can be from 3 to 15V, depending on the supply voltage of the electronic clock circuit, or rather, on the required value of the logic level.

Snegirev I. RK-11-16.

Low Harmonic Test Signal Generator on the Wien Bridge

When not at hand quality sine wave generator- how to debug an amplifier that you are developing? You have to use hand tools.

In this article:

• High linearity when using a budget op amp
• Precise AGC for minimal distortion
• Battery Operability: Minimum Interference

background

At the beginning of the millennium, we, as a whole family, went to live in distant lands. Some of my electronic inventory followed us, but, alas, not all. So I found myself face to face with large monoblocks I had assembled, but not yet debugged at all, without an oscilloscope, without a signal generator, with a great desire to complete that project and finally listen to music. The oscilloscope was begged from a friend for temporary use. With the generator, I had to urgently invent something myself. At that time, I was not yet familiar with the component suppliers available here. Of the opamps that happened to be at hand, there were several indigestible products of the ancient Soviet electronic industry, and the LM324, soldered from a burned-out computer power supply.
LM324 datasheet: National/TI , Fairchild , OnSemi ... I love reading datasheets from National - they usually have a lot of interesting use cases. OnSemi in this case also fussed. But "Gypsy" something deprived his followers 🙂

Classics of the genre

Help the author!

This article showed a few simple tricks that allow you to achieve very high-quality generation and amplification of a sinusoidal signal, using a widely used inexpensive operational amplifier and a p-n junction field-effect transistor:

• Limiting the range of automatic level control and reducing the influence of the non-linearity of the regulating element;
• Offset of the output stage of the op-amp in a linear mode of operation;
• Select the optimal virtual ground level for battery operation.

Was everything clear? Did you find anything new, original in this article? I will be pleased if you leave a comment or ask a question, as well as share the article with your friends on a social network by "clicking" the corresponding icon below.

Supplement (October 2017) Caught on the web: http://www.linear.com/solutions/1623 . Made two conclusions:

1. There is nothing new under the sun.
2. You would not be chasing, pop, for cheapness! I would have taken a normal op-amp then - and I would have received an exemplary low Kg.

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The proposed sine wave test tone generator is based on a Wien bridge, produces very low sine wave distortion, and operates from 15 Hz to 22 kHz in two sub-bands. Two levels of output voltages - from 0-250 mV and 0-2.5 V. The circuit is quite simple and is recommended for assembly even by inexperienced radio amateurs.

Audio Generator Parts List

• R1, R3, R4 = 330 ohm
• R2 = 33 Ohm
• R5 = 50k dual potentiometer (linear)
• R6 = 4.7k
• R7 = 47k
• R8 = 5k potentiometer (linear)
• C1, C3 = 0.022uF
• C2, C4 = 0.22uF
• C5, C6 = 47uF electrolytic capacitors (50v)
• IC1 = TL082 double op amp with socket
• L1 = 28V/40mA lamp
• J1 = BNC connector
• J2=RCA Jack
• B1, B2 = 9V Krone

Generator Assembly

The LED serves as an on/off indicator for the device. Regarding the L1 incandescent lamp, many types of light bulb were tested during the assembly process and all worked well. Start by cutting the PCB to the right size, etching, drilling and assembling.

In amateur radio practice, it often becomes necessary to use a sinusoidal generator. Its applications can be found in a wide variety of ways. Consider how to create a sinusoidal signal generator on the Wien bridge with a stable amplitude and frequency.

The article describes the development of a sinusoidal signal generator circuit. You can also generate the desired frequency programmatically:

The most convenient, from the point of view of assembly and adjustment, a variant of a sinusoidal signal generator is a generator built on the Wien bridge, on a modern Operational Amplifier (OA).

Wine Bridge

The Wien bridge itself is a bandpass filter consisting of two . It emphasizes the center frequency and suppresses the rest of the frequencies.

The bridge was designed by Max Wien in 1891. On a circuit diagram, the Wien Bridge itself is usually depicted as follows:

Image borrowed from Wikipedia

A Wien bridge has an output-to-input voltage ratio b=1/3 . This is an important point, because this coefficient determines the conditions for stable generation. But more on that later

How to calculate the frequency

Self-oscillators and inductance meters are often built on the Wien bridge. In order not to complicate their lives, they usually use R1=R2=R And C1=C2=C . Thanks to this, the formula can be simplified. The fundamental frequency of the bridge is calculated from the ratio:

f=1/2πRC

Almost any filter can be thought of as a frequency dependent voltage divider. Therefore, when choosing the values ​​​​of the resistor and capacitor, it is desirable that at the resonant frequency the complex resistance of the capacitor (Z) be equal to, or at least one order of magnitude, with the resistance of the resistor.

Zc=1/ωC=1/2πνC

Where ω (omega) - cyclic frequency, ν (nu) - linear frequency, ω=2πν

Wien bridge and operational amplifier

The Wien bridge itself is not a signal generator. For generation to occur, it should be placed in the positive feedback circuit of the operational amplifier. Such an oscillator can also be built on a transistor. But the use of an op-amp will clearly simplify life and give better performance.

C grade gain

Wien's bridge has a transmittance b=1/3 . Therefore, the generation condition is that the op-amp must provide a gain equal to three. In this case, the product of the transmission coefficients of the Wien bridge and the gain of the op amp will give 1. And the specified frequency will be generated stable.

If the world were ideal, then by setting the required gain with resistors in the negative feedback circuit, we would get a ready-made generator.

This is a non-inverting amplifier and its gain is given by:K=1+R2/R1

But alas, the world is not perfect. ... In practice, it turns out that in order to start generation, it is necessary that at the very initial moment the coefficient. the gain was slightly more than 3, and then for stable generation it was maintained equal to 3.

If the gain is less than 3, then the generator will stall, if more, then the signal, having reached the supply voltage, will begin to distort, and saturation will occur.

When saturated, the output will be maintained at a voltage close to one of the supply voltages. And random chaotic switching between supply voltages will occur.

Therefore, when building a generator on a Wien bridge, they resort to using a non-linear element in the negative feedback circuit that regulates the gain. In this case, the generator will balance itself and maintain the generation at the same level.

Amplitude stabilization on an incandescent lamp

In the most classic version of the Wien bridge generator on the op-amp, a miniature low-voltage incandescent lamp is used, which is installed instead of a resistor.

When such a generator is turned on, at the first moment, the lamp coil is cold and its resistance is low. This contributes to the start of the generator (K>3). Then, as it heats up, the coil resistance increases and the gain decreases until it reaches equilibrium (K=3).

The positive feedback loop in which the Wien bridge was placed remains unchanged. The general circuit diagram of the generator is as follows:

The positive feedback elements of the op amp determine the generation frequency. And the elements of negative feedback are amplification.

The idea of ​​using a light bulb as a control element is very interesting and is still used today. But the light bulb, alas, has a number of disadvantages:

• selection of a light bulb and a current-limiting resistor R* is required.
• with regular use of the generator, the life of the light bulb is usually limited to a few months
• the control properties of the light bulb depend on the temperature in the room.

Another interesting option is to use a directly heated thermistor. In fact, the idea is the same, only a thermistor is used instead of a bulb spiral. The problem is that you first need to find it and again pick it up and current-limiting resistors.

Amplitude stabilization on LEDs

An effective method for stabilizing the amplitude of the output voltage of a sinusoidal signal generator is the use of LEDs in the negative feedback circuit of the op amp ( VD1 And VD2 ).

The main gain is set by resistors R3 And R4 . The rest of the elements ( R5 , R6 and LEDs) regulate the gain in a small range, keeping the generation stable. resistor R5 you can adjust the output voltage in the range of approximately 5-10 volts.

In the additional OS circuit, it is desirable to use low-resistance resistors ( R5 And R6 ). This will allow a significant current (up to 5mA) to pass through the LEDs and they will be in optimal mode. They will even glow a little :-)

In the diagram shown above, the Wien bridge elements are designed to generate at a frequency of 400 Hz, however, they can be easily recalculated for any other frequency using the formulas presented at the beginning of the article.

Quality of generation and applied elements

It is important that the operational amplifier can provide the necessary current for generation and has sufficient frequency bandwidth. The use of folk TL062 and TL072 as op amps gave very sad results at a generation frequency of 100 kHz. The waveform was hardly sinusoidal, rather it was a triangular signal. Using the TDA 2320 gave an even worse result.

But the NE5532 showed itself from the excellent side, giving out a signal very similar to a sinusoidal at the output. The LM833 also did an excellent job. So it is NE5532 and LM833 that are recommended for use as affordable and common high-quality op-amps. Although with a decrease in frequency, the rest of the op-amps will feel much better.

The accuracy of the generation frequency directly depends on the accuracy of the elements of the frequency-dependent circuit. And in this case, it is important not only to match the face value of the inscription element on it. More accurate parts have better value stability with temperature changes.

In the author's version, a resistor of the C2-13 ± 0.5% type and mica capacitors with an accuracy of ± 2% were used. The use of resistors of this type is due to the small dependence of their resistance on temperature. Mica capacitors also depend little on temperature and have a low TKE.

Cons of LEDs

On LEDs it is worth dwelling separately. Their use in a sine generator circuit is caused by the magnitude of the voltage drop, which usually lies in the range of 1.2-1.5 volts. This allows you to get a sufficiently high value of the output voltage.

After the implementation of the circuit, on the breadboard, it turned out that due to the spread of the parameters of the LEDs, the fronts of the sinusoid at the output of the generator are not symmetrical. It's a bit noticeable even in the photo above. In addition, there were slight distortions in the generated sine shape, caused by the insufficient speed of the LEDs for a generation frequency of 100 kHz.

Diodes 4148 instead of LEDs

The LEDs have been replaced with the beloved 4148 diodes. These are affordable fast signal diodes with switching speeds of less than 4 ns. At the same time, the circuit remained fully functional, there was no trace of the problems described above, and the sinusoid acquired an ideal form.

In the following diagram, the fault bridge elements are designed for an oscillation frequency of 100 kHz. Also, the variable resistor R5 was replaced with constant ones, but more on that later.

Unlike LEDs, the voltage drop at the p-n junction of conventional diodes is 0.6÷0.7 V, so the output voltage of the generator was about 2.5 V. To increase the output voltage, it is possible to turn on several diodes in series, instead of one, for example like this:

However, increasing the number of non-linear elements will make the generator more dependent on the external temperature. For this reason, it was decided to abandon this approach and use one diode at a time.

Replacing a variable resistor with constant ones

Now about the tuning resistor. Initially, a 470 ohm multi-turn trimmer was used as resistor R5. It allows you to accurately adjust the output voltage.

When building any generator, it is highly desirable to have an oscilloscope. The variable resistor R5 directly affects the generation - both the amplitude and the stability.

For the presented circuit, the generation is stable only in a small range of resistances of this resistor. If the resistance ratio is greater than required, clipping begins, i.e. the sine wave will be clipped at the top and bottom. If it is less, the shape of the sinusoid begins to be distorted, and with a further decrease, the generation stalls.

It also depends on the supply voltage used. The described circuit was originally assembled on an LM833 op amp with ± 9V power supply. Then, without changing the circuit, the op-amps were replaced with AD8616, and the supply voltage was ± 2.5V (the maximum for these op-amps). As a result of such a replacement, the sinusoid at the output was cut off. The selection of resistors gave values ​​​​of 210 and 165 ohms, instead of 150 and 330, respectively.

How to choose resistors "by eye"

In principle, you can leave a tuning resistor. It all depends on the required accuracy and the generated frequency of the sinusoidal signal.

For self-selection, you should, first of all, install a tuning resistor with a nominal value of 200-500 Ohms. By applying the output signal of the generator to the oscilloscope and rotating the tuning resistor, reach the moment when the limitation begins.

Then, lowering the amplitude, find the position in which the shape of the sinusoid will be the best. Now you can unsolder the trimmer, measure the resulting resistance values ​​​​and solder the closest values.

If you need an audio frequency sine wave generator, you can do without an oscilloscope. To do this, again, it is better to reach the moment when the signal, by ear, begins to distort due to clipping, and then reduce the amplitude. You should decrease until the distortion disappears, and then a little more. This is necessary because by ear it is not always possible to catch distortion even in 10%.

Additional Gain

The sine generator was assembled on a dual op-amp, and half of the microcircuit was left hanging in the air. Therefore, it is logical to use it under an adjustable voltage amplifier. This made it possible to transfer the variable resistor from the additional oscillator circuit to the voltage amplifier stage to adjust the output voltage.

The use of an additional amplifying stage guarantees a better matching of the generator output with the load. It was built according to the classical scheme of a non-inverting amplifier.

The specified ratings allow you to change the gain from 2 to 5. If necessary, the ratings can be recalculated for the required task. The stage gain is given by:

K=1+R2/R1

Resistor R1 is the sum of series-connected variable and fixed resistors. A fixed resistor is needed so that at the minimum position of the variable resistor knob, the gain does not go to infinity.

How to strengthen the exit

The generator was supposed to work on a low-resistance load of a few ohms. Of course, not a single low-power op-amp will be able to deliver the required current.

For power, a repeater on the TDA2030 was placed at the output of the generator. All the goodies of this application of this microcircuit are described in the article.

And this is how the circuit of the entire sinusoidal generator with a voltage amplifier and a follower at the output actually looks like:

The sine generator on the Wien bridge can also be assembled on the TDA2030 itself as an op-amp. It all depends on the required accuracy and the selected generation frequency.

If there are no special requirements for the quality of generation and the required frequency does not exceed 80-100 kHz, but it is supposed to work on a low-resistance load, then this option is ideal for you.

Conclusion

The Wien bridge generator is not the only way to generate a sine wave. If you need high-precision frequency stabilization, then it is better to look towards oscillators with a quartz resonator.

However, the described circuit is suitable for the vast majority of cases when it is required to obtain a stable, both in frequency and amplitude, sinusoidal signal.

Generation is good, but how to accurately measure the magnitude of high-frequency alternating voltage? For this, a scheme called is perfect.

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