Strengthening Open-Loop Op-Amp

The op-amp ideally has an infinite open-loop gain (AOL). In practice, however, op-amps such as LM741 have a finite amplification of approximately 100,000 times. Actually with this bigger gain, the op-amp gain system becomes unstable. Very small differential inputs can already make the outputs a manifestation. In the next chapter will discuss how feedback can make the op-amp’s reinforcement system stabilized.

A. Unity-Gain Frequency
The ideal Op-Amp should work at any frequency ranging from dc signal to Herzt giga frequency. Unity-gain frequency parameter becomes important if the op-amp is used for certain frequency applications. Parameter AOL is usually a gain of op-amp on DC signal.

Response of op-amp gain decreases as the input signal frequency increases. Op-amp LM741 for example has unity-gain frequency of 1MHz. This means the amplification of the op-amp will be 1 time at 1 MHz frequency. If you need to design the application at high frequency, then choose op-amp that has higher unity-gain frequency.

B. Op-Amp Ideal
Op-Amp is basically a differential amplifier that has two inputs. Input (input) op-amps as already understandable there are so-called inverting and non-inverting inputs. The deal op-amp has an infinite open loop gain. Like the LM741 op-amp often used by many electronics practitioners, it has the typical characteristics of an open loop gain of 10 ⁴ ~ 10 ^{5 This} magnitude gain makes the op-amp unstable, and its gain becomes infinite.

This is where the role of the negative feedback circuit is required, so that the op-amp can be assembled into an application with a measured value of finite. The ideal op-amp input impedation should be infinite, so that the input current at each input should be 0. As a practical comparison, the LM741 op-amp has an input impedance Z _in = 10 ⁶ Ohm. The impedance value is still relatively large so the input current of the LM741 op-amp should be very small.

There are two important rules for analyzing op-amp circuits based on ideal op-amp characteristics. This rule in some literature is called golden rule, namely:

These are two important rules of ideal op-amps used to analyze op-amp circuits.

C. Inverting Amplifier
The inverting amplifier base circuit as shown in Figure 1, where the input signal is generated through the inverting input. As the name implies, the reader would have guessed that the output phase of this inverting amplifier would always be in reverse with the input. In this circuit, negative feedback is generated through resistor R2.

Inverter Drawer Image

The non-inverting input in the circuit is grounded, or v ₊ = 0. With rule 1 (see rule 1), it will be dipenuhiv _– = v ₊ = 0. Since the value is 0 but not directly connected to ground, the op-amp- In this circuit is called virtual ground. With this fact, it can be calculated the clamp voltage at R1 is v _in -v = vin and the clamp voltage of the reactor R2 is v _out -v _– = v _out Then by using rule 2, it is known that: i _in + i _out = I = 0, Because according to rule 2, the input current of the op-amp is 0 i _in + i _ou t = v _in / R ₁ + v _out / R ₂ = 0 Next vout / R2 = -v _in / R1 or v _out / v _in = -R2 / R1