Follow voltage op amp circuit shown in Figure 1, the use of virtual short Virtual Open, a look is simple, nothing too much content needs to pay attention, you might think again. Appreciated luck discharge voltage circuit following, for understanding the op amp, reverse-phase, differential, and the various op amp circuit, are of great help.
Voltage following circuit analysis
if we connect the output of operational amplifier to its inverting input terminal, then a voltage signal is applied to the noninverting input, we find that the output voltage of the op amp will recover well as the input voltage.
Suppose the initial state of the op amp input and output voltages are 0V, then when Vin starts to increase from 0V time, Vout of it will increase, and increasing toward the positive voltage. This is because the sudden increase assuming Vin, Vout of 0V yet still no response time, Ve = Vin-Vout is greater than 0, the open-loop gain is multiplied by the operational amplifier, Vout = Ve * A, so that the op amp's output Vout begins to increase toward the positive voltage.
As with the Vout increases, the output voltage is fed back to the inverting input of the operational amplifier decreases and the pressure difference between the two inputs, i.e. Ve decreases, in the case of the same open loop gain next, Vout will naturally be reduced. The end result is, no matter how much input is the input voltage (of course, in the op amp's input voltage range), the amplifier will always be very close to the output of a voltage Vin, but this is just below the output voltage Vout Vin to the op amp is available to ensure a sufficient voltage difference Ve between the two input terminals, the op amp output is maintained, i.e. Vout = Ve * a.
Operational amplifier negative feedback circuit
then the circuit will quickly reach a steady state, the magnitude of the output voltage will be accurately maintained pressure differential between the two amplifier input terminals, the differential pressure in turn produces Ve the exact magnitude of the output voltage of the op amp. The op amp's output and the inverting input of op amp connected, in such a manner is referred to as negative feedback from the system to achieve this is the key to stability. This applies not only to the op amp, the same applies to any common dynamic system. This includes the ability to stabilize such amplifier operating in the linear mode, rather than just in a saturated state, all "on" or all "off", as it has no comparator is used for negative feedback of the same.
Because of the high gain amplifier, the inverting input of op amp voltage maintained almost equal to Vin. For example, an operational amplifier open loop gain of 200,000. If Vin is equal to 6V, the output voltage at this time was 5.999 970 000 149 999V. This op amp input produces enough voltage differential Ve = 6V-5.999 970 000 149 999V = 29.999 85uV, this voltage is amplified and generated amplitude 5.999 970 000 149 999V voltage at the output, so that the system It will stabilize here. As you can see, 29.999 85uV is a small voltage, for actual calculation, we can think to maintain negative feedback amplifier by a differential pressure between the two input terminals Ve = 0V, the process shown in FIG 2 shows. This is what we are familiar with "virtual short", but due to the impedance between the two input terminals of the op amp is great, naturally have a "false break." The following circuit having a stable 1 times the closed loop gain, the output voltage will simply follow the input voltage.
A big advantage of using negative feedback is that we do not have to care about the actual voltage gain of the op amp, as long as it is large enough can be. If the voltage gain of the op amp 250 000 but not 2,000,000, which causes the output voltage of the op amp will be closer to some of Vin, the voltage difference between the smaller input used to generate the required output voltage. In the circuit illustrated in FIG. 2, the same output voltage will equal the input voltage at the op amp's inverting input terminal. Thus, the circuit design for engineers, in order to achieve stable closed-loop gain of the amplifier circuit, the open loop gain of the amplifier is not necessarily an exact value, the negative feedback makes the system self-adjustment.
Negative feedback improves the linearity, gain stability, accuracy of the output impedance, gain, but negative feedback will also bring about a serious problem, that is, reducing the stability of the system, and follow the voltage of the circuit is unity gain this is a worst-case scenario, especially in the case of driving a capacitive load, interested students can go to access relevant information themselves.
About op amp circuit, many times we have been taught to follow the phase inverting terminal end of the same, as stated earlier, it really can not follow the same phase-inverting terminal end of it?
For today follow speaking voltage circuit, it can only follow the phase inverting terminal end is the same. Here because if voltage is applied to a positive input, the output is connected to a noninverting terminal, assuming the same output as 0, that would be a negative Ve voltage, multiplied by the open loop gain op amp, then the output would be at the inverting terminal a negative voltage returns to the non-inverting input terminal of the op amp will further get a larger absolute value of the negative voltage difference. Soon op amp's output will reach saturation, naturally can not achieve the same end following the phase inverting terminal.
But for op amps, if the reference voltage is applied at the inverting terminal, with the other electronic components, such as transistors, the MOS, etc., so that overall loop forming a negative feedback amplifier, the noninverting terminal can also follow the inverting terminal, this naturally broke the familiar inverting terminal of the op amp to follow the law with phase ends.
Put voltage circuit following operation, "virtual short", "false break" is a surface, the negative feedback is the root. Based on this root, it may well help us to understand the ever-changing op amp circuit.
