Capacitor three-point lc oscillator circuit _ capacitor three-point lc oscillation frequency calculation

A three-point capacitor oscillator is an electronic component, also known as a Colpitts oscillator, which is a self-excited oscillator. The series capacitor and the inductor loop and the positive feedback amplifier are named because the three end points of the two series capacitors of the oscillation circuit are respectively connected with the three pins of the oscillation tube.

Advantages and disadvantages

The advantage of this circuit is that the output waveform is good and the oscillation frequency can be above 100 MHz. The disadvantage is that it is inconvenient to adjust CC1 and CC2 at the same time when adjusting the frequency. Suitable for stationary oscillators.

The following is a reliable and practical wireless microphone: The amplifier circuit composed of BG1 amplifies the weak sound signal detected by the small condenser microphone, and reaches a certain amplitude and then sends it to the capacitor three-point oscillator composed of BG2 to modulate the carrier signal generated by BG2. And finally output from the antenna. The circuit uses diode voltage regulation technology to make the circuit work more stably. The circuit is as follows:

Component selection

BG1 uses 2SC9014 equivalent Power Transistor. BG2 selects 2SC9018 and other high frequency and high power triodes, which requires β≥100. The MIC uses miniature ultra-thin condenser microphones. L1 is made up of 8 turns of Φ51mm high-strength enameled wire on the ballpoint pen core, and parallel resonance with C4 is about 100MHZ.

The capacitor three-point LC oscillator circuit is also called the Colpitts oscillator circuit. It is similar to an inductive three-point LC oscillating circuit, except that the capacitive element and the inductive element are interchanged. As shown in Figure 1.

Figure 1 Capacitor three-point LC oscillator circuit

Under the condition that the Q value of the LC resonant circuit is sufficiently high, the oscillation frequency of the circuit is

The characteristic of the oscillating circuit is that the oscillating frequency can be made higher, generally reaching 100 MHz or more. Since the impedance of the C2 to the higher harmonics is small, the higher harmonic components in the feedback voltage are smaller, and thus the oscillating waveform is better. The disadvantage of the circuit is that the frequency adjustment is inconvenient. This is because when the capacitance is adjusted to change the frequency (even if C1 and C2 are double-connected variable capacitors), C1 and C2 are also difficult to scale, which causes instability of the circuit performance. Therefore, the circuit is only suitable for generating a fixed frequency oscillation.

Figure 2 Three-point oscillating circuit composed of integrated circuits

A three-point LC oscillator similar to the inductor three-point LC oscillator is shown in Figure 1. The analysis method is the same as that of the inductor three-point LC oscillator. When the positive and negative feedback is judged by the instantaneous polarity method, the output voltage of the triode or op amp will be distributed on the LC parallel circuit. The capacitor branch is composed of C1 and C2 connected in series, and the voltage on the capacitor is inversely proportional to the capacity of the capacitor, and is proportional to the inductance in the three-point oscillating circuit of the inductor.

The feedback voltage of the oscillating circuit of Figure 1 is taken out from capacitor C2, that is, the voltage of C2 to ground. If the feedback voltage is insufficient, the capacitance should be appropriately reduced. Oscillation frequency The oscillation frequency of the circuit of Figure 1 is: