RC Oscillator and active filter 1

Self-summary, there are mistakes welcome to point out!

First, the principle of the oscillator:

For positive feedback, there are the following formulas:

Discuss:

1. When a*f (JW) = 1 o'clock af→∞ (physical meaning: self-oscillating);

2. On the F0, the F (JW) phase shifts to 0 or 2n∏ (therefore, the amplification effect at F0 is most obvious, and if there is a phase difference, the XF and XI two signals will be reduced after stacking. ）

3. As an amplifier, a*f (JW) is unlikely to ≥1, but may <1; (equals 1 will trigger self-oscillation, greater than 1 output signal XO will increase indefinitely until the supply voltage is reached or the waveform is distorted due to transistor limitations)

4. When a*f (JW) <1, there is no oscillation, but at this point af>a, positive feedback leads to increased gain.

Conclusion:

The oscillator is essentially an active bandpass filter when the amplitude condition is not satisfied. (The magnification effect is most obvious at F0, and the amplification effect is lower or higher than F0, and the band-Pass law is present)

Second, the Venturi bridge oscillator

1. The transmission function of the feedback network:

2. Amplitude-frequency characteristics of feedback networks

Take F0 for 100Hz mapping:

3. Phase-frequency characteristics of the feedback network

Take F0 for 100Hz mapping:

4. Characteristics of the Feedback network transfer function of the Venturi bridge oscillator

① at F=fo, the feedback coefficient is a constant of 1/3 and is the maximum value.

② at F=FO, the phase shift of the feedback network is 0 (so the feedback coefficient is a constant).

Although the ③ feedback coefficient has a band-pass property, the curve is extremely flat.

④ in F FO, it is equivalent to a low-pass network, so it has a negative phase shift.

RC Oscillator and active filter 1