In LC oscillators, what is the feedback introduced to make it easy to vibrate?

The difference between an LC resonant circuit and an LC oscillation circuit.

LC resonant circuit is a signal processing circuit, which must have an input signal, and the input signal frequency is correlated, and the output signal spectrum can be wide or narrow, depending on the requirements; The LC oscillation circuit is the place where the periodic signal is generated, and its output is approximately that of the LC oscillation circuit of a single frequency signal.

LC oscillation circuit refers to the oscillation circuit composed of frequency selection network with inductor L and capacitor C, which is used to generate high-frequency sine wave signals, and the common LC sine wave oscillation circuits include transformer feedback LC oscillation circuit, inductance three-point LC oscillation circuit and capacitor three-point LC oscillation circuit. The radiated power of the LC oscillation circuit is proportional to the fourth power of the oscillation frequency, and in order for the LC oscillation circuit to radiate strong enough electromagnetic waves, the oscillation frequency must be increased and the circuit must have an open form.

The LC oscillation circuit uses the energy storage characteristics of capacitance and inductance to convert electromagnetic energy alternately, that is to say, there will be a maximum and minimum value of electrical energy and magnetic energy, and there will be oscillation. However, this is only an ideal situation, in fact, all electronic components will have losses, energy in the process of conversion between capacitance and inductance is either lost, or leaked out of the outside, energy will continue to decrease, so the actual LC oscillation circuit needs an amplification element, either a transistor, or an integrated op amp equal number of electric LC, using this amplification element, through a variety of signal feedback methods to make the constantly consumed oscillation signal is feedback amplified, As a result, a signal with stable amplitude and frequency is finally output. The formula for calculating the frequency is f=1 [2 (lc)], where f is the frequency in hertz (Hz); l is the inductance, the unit is henry (h); c is the capacitance and the unit is farad (f).

There are two types of feedback: positive feedback and negative feedback.

In the oscillator, positive feedback must be introduced.

Otherwise, it can't oscillate, and it's not an oscillator.

Why is automatic pneumatics easy to cause feedback? I feel like if you want to know what this feedback is, you have to make the vibrator a large frequency so that you can know how to share it. Every day.

The amplitude of the output voltage of the LC oscillator is unstable, which will affect the stability of the frequency, and the CE affects the transistor oscillation period (differential frequency) oscillation waveform waveform stable transmission, that is, the main power of the RC whole module, the more current the resistance, that is, the more basic the transmission power.

If the output signal is sent back to the input loop by the LC resonant loop through mutual inductance coupling, a mutual inductance coupled oscillator is formed. It is important to place the correct position of the eponymous end of the coupling coil and select the appropriate coupling amount m to meet the amplitude and vibration conditions.

There are three types of mutual inductive coupled oscillators: base modulation circuits, mobilization circuits, and modulation circuits. From the definition of the name of the mutual inductance coupling contract, it can be concluded that the feedback network forms positive feedback and satisfies the phase equilibrium condition.

CE affects the transistor oscillation period (differential frequency), oscillation waveform, waveform, stable transmission, that is, RC, the main power of the whole module, the current transmission, the resistance, the more current that is, the more basic the transmission power, the more basic calculation CE I determine the calculation.

Answer]: The two joints of the feedback coil can be activated after being reversed, indicating that the polarity of the feedback coil in the original circuit is reversed, forming negative feedback and cannot vibrate. $Change rb1

RB2 or RE

The resistance adjusts the static operating point of the circuit. Regulate RB1

RB2 or RE

After the resistance value, it can vibrate, indicating that the working point of the original power Lingzi Road is low, and the voltage amplification factor is small; After adjusting the working point, the voltage amplification factor is increased, so it can rise and vibrate. The transistor can vibrate after using a larger tube, indicating that the original circuit is too small, so that the voltage amplification factor does not meet the amplitude condition of self-oscillation. Switching to a larger transistor can increase the voltage amplification factor and make it easier to oscillate.

Increasing the number of turns of the feedback coil can vibrate, indicating that the feedback strength in the original circuit is not enough to vibrate. Increasing the number of turns of the feedback coil increases the amount of feedback and makes the circuit easy to vibrate.

1. The LC element only works on the AC voltage (current), the DC is invalid (L is equal to the wire, C is equal to the open circuit), usually the DC input of the oscillator is added to the transistor and other devices as the oscillation energy, not to the LC. With high voltages, the transistor may output a larger oscillating wavepattern.

3. To expand the antenna effect of L, it is necessary to increase the diameter of the coil. Since the current velocity is the speed of light, when the length of the wire is long enough, the high-frequency current on the wire is no longer in phase, some areas are in positive half cycle, and some are in negative half cycle, as described in the middle figure, a positive and negative half cycle alternately called a wavelength. Coiling up a wavelength of the wire (the ring antenna hung on the old black-and-white TV), or folding, as shown in the figure on the right, is the folding oscillator outdoor antenna used in the TV, you can find that the current direction of the a, b, and c regions on the middle diagram is unified, and everyone is working together, rather than dismantling each other.

But as the energy is emitted, the energy consumed will be converted into the equivalent resistance of the coil, when you completely transform the coil into an antenna, it is no longer L, as we all know, this kind of TV antenna is equal to a pure resistance of 300!

4. The same C internal electric field can not go out, if the two plates of the capacitor are gradually pulled apart, then the electric field gradually leaks out, if it is pulled into a piece of heaven and an underground piece, it becomes a pull rod antenna. You can see that the old radio antenna during the Anti-Japanese War also had several blades on the top, which is the plate that replaces the capacitor, and the other plate of the capacitor is the ground or chassis bottom plate. But the modified component is not C, it is a 50 impedance whip antenna.

5. To sum up, the LC resonant circuit should not be used as an antenna, and the more it is transformed to look like an antenna, the farther away from the resonance function.

6. The inductor current can not be abruptly changed, the capacitance voltage cannot be abruptly changed, and the LC loop can not produce pulses, only sine waves, and the rich high-order harmonic components in the pulse wave are filtered out by the LC circuit.

7. If you only use L and do not use C, using the principle that the current of L cannot be abruptly changed, and suddenly turn off the current in L with a switch, it is possible to induce a high-voltage pulse. However, it often penetrates the switching device that shuts it off, and it is necessary to be careful to deal with the problem in the switching power supply.

8. Calculation method of oscillation frequency: open the root after multiplying LC, and then multiply by 2 to take the reciprocal. To increase the oscillation frequency, decrease the values of l and c.

9. The oscillation circuit includes two parts: the LC loop and the amplifier for frequency selection, the frequency is determined by the LC loop, the power is determined by the output power of the amplifier, and the level of the input DC voltage has an impact on it, which has been explained in point 1.

I don't know what industry the landlord is doing? As the signal source frequency of information technology, to obtain a large signal power, it is usually not to increase the output power of the oscillator, but to add a power amplifier to achieve it; As an energy technology, the oscillation waveform does not take this road, but uses high-power oscillators, which are more energy efficient but some other indicators are not very good, such as induction cookers and microwave ovens.

When capacitance c remains unchanged, the larger the incoming inductance l is, the oscillation source.

The longer the period t, the lower the frequency;

When the inductance l is constant, the larger the capacitance c is, the longer the oscillation DAO period and the lower the frequency

When the L and C values remain the same, the speed of the watch hand swing is the same (only the number of swings is different).

The natural period (t) and natural frequency (f) of the LC oscillation circuit are determined by the inductance l of the coil and the capacitance c of the capacitor in the circuit

The larger the capacitance, the more charge it holds, and the longer it takes to charge and discharge, so the longer the cycle and the lower the frequency; The larger the inductance L of the coil, the stronger the delay effect that hinders the change of current, so that the longer the time for discharging and charging, and thus the longer the period, the lower the frequency In summary, the period and frequency of the LC circuit are determined by the properties of the circuit itself (the value of L and C), and have nothing to do with the amount of charge and current of the capacitor

RC bridge oscillator requires the amplification of the amplifier to be equal to 3, if the negative feedback is weak, the amplification will be too much to distort the waveform; If the negative feedback is too strong and the magnification is less than or equal to 3, it is difficult to start vibration or work unstable.

The oscillation circuit, also known as the waveform generator, is a signal generator with no signal input and signal output, which is generally composed of an amplification circuit and an oscillation frequency selection circuit, with a triode and an operation amplification circuit.

The frequency selection circuit is generally composed of a resistor capacitor, that is, a RC oscillation frequency selection circuit; Or it is composed of inductive capacitors, i.e., LC oscillation circuits. The oscillation circuit is divided into sinusoidal filter oscillator and non-sine wave oscillator according to the waveform generated by the oscillation; According to the principle of generating oscillators, they are divided into feedback type and negative resistance type.

Answer]: In an LC oscillation circuit, neither the phase shift of the transistor nor the phase shift of the feedback network can be equal to 0, i.e., Fe

f0, so in order to satisfy the phase equilibrium condition of the oscillation, fe f z0, the lc resonant loop must provide z

The phase shift of fe f, which is the phase shift z when the resonant loop resonates

0, it can be seen that only when the oscillation frequency is not equal to the resonant frequency of the resonant loop, the resonant loop works in the state of loss of harmony, and it can provide the phase shift value required by the phase equilibrium condition.

Since the frequency stability of the LC oscillator is related to the rate of change of the phase frequency characteristics of the resonant loop on the oscillation frequency, the greater the rate of change, the higher the stability of the oscillation frequency. When the resonant loop is detuned, the rate of change of its phase shift characteristics decreases, so the frequency stability of the oscillator decreases. Therefore, the phase shift of the transistor and the phase shift of the feedback network should be reduced as much as possible in the actual oscillation circuit, and the closer the oscillation frequency is to the loop resonant frequency, the better.

Answer]: The parallel resonant circuit has resonance characteristics, that is, when the frequency of the applied signal is equal to the resonant frequency of the loop, when the loop is tuned, the output voltage at both ends of the loop is maximum, and the phase shift is zero; When the applied signal frequency is not equal to the positive or vibrating frequency of the harmonic limb of the loop, and the loop is detuned, the voltage at both ends of the loop decreases rapidly, and the phase shift value increases.

Using the resonance characteristics of the loop, through tuning, the useful signal can be selected from the sum of various signals of different frequencies and the unwanted signal can be filtered out, which is called the frequency selection of the resonant loop for the first purpose. The larger the q value of the resonant loop, the sharper the loop resonance curve, the better its frequency selection, but the pass band will be narrower.

When the LC parallel resonant circuit resonates, the voltage at both ends of the circuit reaches the maximum.

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