In the application of integrated op-amp, through integrated operational in most applications of phase compensation is to be able to meet the requirements.
But in the application, and sometimes appear self-excitation, this is typically due to the following reasons.
Recommended in the instructions for compensation methods and parameters, through the product design and a large number of experiments, is effective for most applications, it takes into consideration the factors such as temperature, power supply voltage change caused by the change of the frequency response characteristics, and to ensure that the stability margin, has certain aluminum electrolytic capacitor
s because of its high inductance, affect the decoupling effect.
Second, the power supply decoupling is bad when the power supply decoupling, the zoom level of the signal current impedance voltage drops on the mutual coupling effect, if the coupling signal and MouJi in phase with the input signal is, the circuit will produce parasitic oscillation.
Therefore we must attach importance to the power supply decoupling.
Decoupling in addition to the supply side large capacitor added, should also be small capacitance and ceramics, because large capacitance, such as the electrolytic capacitor and its distribution inductance is bigger, affect the decoupling effect.
Three, circuit connection of distributed capacitance effects due to the distributed capacitance to exist in a circuit, sometimes by distributed capacitance signal level after feedback to the former level, when the feedback signal and the amplifier stage in phase with the original input signal, also can form parasitic positive feedback, so that the self excited oscillation circuit.
So connection circuit, it is important to try to reduce the distributed capacitance, especially should pay attention to the integrated operational amplifier & other
Input end away from the output end.
Four, integrated op-amp the influence of the load capacitance is too large when integrated op-amp load capacitance is too large, the open loop frequency response curve of the op-amp circuit will change, make the circuit of the phase margin is reduced, and even cause self excitation.
If the output of the op-amp and the external load capacitance ask added a small resistance (
Such as hundreds of Europe)
, make the op-amp circuit and load capacitance between isolated, can reduce the influence of the load capacitance.
But sometimes the effect of this improvement is limited.
To eliminate self-excited oscillation, should reduce the load capacitance, or on the integrated operational amplifier output end and the output power more better output stage circuit, high frequency response.
Five, integrated op-amp in-phase input end grounding resistance is too large when the in-phase end to access a lot of resistance, with the op-amp input capacitance differential mode, forming a new pole, though at the input capacitance is not big, but with the end of an external resistance is bigger, the new poles may be close to or below the transition frequency, and make the self-excited closed loop circuit or circuit dynamic characteristics.
A simple method to solve is to ground the same phase resistor and capacitor, to form a high-frequency bypass.
Six, integrated op-amp output end with the same phase and zero end of the figures is parasitic capacitance when designing printed circuit board, or circuit experiment, song to lead arrangement inappropriate or too long, too close, will bring self-excitation caused by parasitic capacitance.
Usually in the low frequency circuit, is not easy to appear self-excitation, in broadband amplifier, eliminate the parasitic capacitance coupling should be paid attention to.
The negative electrode of aluminum electrolytic capacitors by soaked in liquid electrolyte (
The tissue paper/film or polymer electrolyte composition;
Manganese dioxide tantalum electrolytic capacitor negative electrode is usually adopted.
Due to the electrolyte as a negative electrode (
Pay attention to and dielectric distinguish)
Thus the name, electrolytic capacitor.
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