Can work normally to let carry put, circuit middling increases electric capacity of one phasic compensation between input and output.

 

Theoretical calculation has is some, but arriving to design mature phase to be like major person is to depend on previously debug experience, be worth the frequency that should consider a system to ring to the extraction of capacitance size commonly (the electric capacity that simple point says to add is larger, bandwidth is narrower) , if you must be calculated,be oscillation problem; next, the inputs end distributinging capacitance that can see carry put is how old, cite a case, the product of the electric capacity that the cost of that resistor block that the block value that negative feedback magnifies circuit wants to assure feedback resistor namely and the product = input of distributinging capacitance carry and you should increase.

 

1) phase shift of change feedback network, compensation carry puts phasic lag

2) the influence that compensates carry to put an input to carry capacitance (still compensate finally actually phasic)

 

The motion that uses because of us puts not be ideal.

The operation amplifier that uses actually commonly has corresponding phase shift effect to the signal of certain frequency, such signal feedbacks to input end to will make magnify circuit works to be not stabilized produce vibration even, the phasic compensation with must add corresponding capacitance to give fair for this. Interior is put in carry general inside buy has compensation electric capacity, of course if the word of need also can be in,circuit China and foreign countries is added, as to its the value depends on signal frequency and circuit character.

 

 

The amplifier that general linear works (the enlarge circuit that introduces negative feedback namely) the stability that inputs parasitism capacitance Cs to be able to affect circuit, its compensate measure to see a picture. The parasitism capacitance Cs that the input of amplifier carries general existence to make an appointment with law of a few skins, this capacitance includes distributinging electric capacity of the input electric capacity that carry puts and wiring, it and feedback resistor Rf form network of a lag, cause output tension phasic lag, when the frequency that should input signal is very tall, the bypass action of Cs makes the high frequency noisy meet an emergency of amplifier poor, the upper limit frequency of its frequency band is about:

 

ωh=1/(2πRfCs)

 

If the block value of Rf is greater, the upper limit frequency of amplifier will drop badly, phasic likelihood causes the add lag that at the same time Cs, Rf introduces parasitism oscillation, can pose serious stability problem consequently. To this, a simple means of settlement is the block cost that reduces Rf, the frequency limits that makes ωh tower above applies actually, but this kind of method will make the voltage of operation amplifier magnifies multiple drops (because of Av=-Rf/Rin) . Magnify to maintain the voltage of enlarge circuit multiple is higher, more current method is go up in Rf and receive Cf of capacitance of a compensation, make Rin Cf network and Rf Cs network form phasic compensation. Rin Cf will cause output tension phasic lead, as a result of cannot accurate the value that knows Cs, so phasic lead capacity and lag quantity get impossibly be compensatinged completely, it is to use alterable capacitance Cf commonly, make add phase shift the least with experiment and the method that adjust Cf. Be like Rf=10kΩ , the model of Cf is worth 10pF of the 3 ～ side silk. Follow to voltage implement, its Cf value is OK and a few more largish.

 

To circuit of a lot of compositive operation enlarge, if output is laden the value of capacitance CL is a lot of greater than 100pF, because output capacitance (include parasitism electric capacity) will cause add phase shift with output resistor, of this add phase shift cumulative produce parasitism vibration possibly, make amplifier works to be not stabilized badly. The method that solves this one problem is to carrying put output carries series Ro of a resistor, make laden capacitance CL and enlarge circuit be apart leave, if plan institute is shown, feedback resistor Rf is received at the back of of Ro, can compensate dc attenuation so, add feedback capacitance Cf to be able to reduce multiple of enlarge of voltage of high frequency closed circuit, of Cf choosing a method is: Make magnify circuit is in the capacitive reactance Xcf≤Rf/10 when FT of unit gain frequency, xf=l/(2πfTCf) , usually, ro=50 ～ 200Ω , cf is 3 ～ 10pF about.

 

Besides afore-mentioned not stable elements, still exist a few otherer not stable element, some are to come from compositive chip oneself. Some are to result from systematic circuit (for example the coupling problem) that the internal resistance of power source fights. Use a lot of methods to solve not stable problem hard sometimes, but after using proper compensation method, can make problem be readily solved. For example. Do not need too broad frequency band and optimal changeover rate when amplifier when, put to compositive carry had used compensatory method to be able to obtain very good result, if will compensate capacitance to increase 9 times or the multiple that needs to realize stability place, be put to μA301 carry and character, its effect is general better.