What Are Integrated Amplifiers?

Integrated operational amplifier (Integrated Operational Amplifier) for short is an integrated operational amplifier, which is a high-gain analog integrated circuit composed of multi-stage direct coupled amplifier circuits.

Since the first monolithic integrated operational amplifier A702 developed by Fairchild in 1964, the integrated operational amplifier has been widely used, and it has become the category with the most variety and quantity in linear integrated circuits.

The national standard unified nomenclature stipulates that the models of various varieties of integrated operational amplifiers are composed of letters and Arabic numerals. The letters in the header use the two CF letters, C is the national standard, F is the linear amplifier, and the following numbers indicate the type of integrated operational amplifier.

Its gain is high (up to 60 ~ 180dB), input

The integrated operational amplifier is a direct-coupled amplifier with a high voltage amplification factor, which is mainly composed of three parts: input, middle, and output. The input part is a differential amplifier circuit, which has two input terminals: in-phase and anti-phase; the voltage change of the former and the voltage change direction of the output are the same, while the latter is the opposite. The middle part provides a high voltage amplification factor, which is transmitted to the load through the output part. Its lead-out terminals and functions are shown in the figure. Among them, the zero-adjusting terminal is externally connected with a potentiometer, which is used for adjusting the voltage of the input terminal to ground (or a predetermined value), and the voltage of the output terminal to ground is also zero (or another predetermined value). The compensation terminal is externally connected with a capacitor or a resistor-capacitor circuit to prevent self-excited oscillation during operation (some integrated operational amplifiers do not require zero adjustment or compensation). The power supply is usually connected in the form of positive to ground or negative to ground, and ground is used as the common terminal of input, output and power.

There are more than 30 parameters that characterize the performance of integrated operational amplifiers, and the following 10 are commonly used.

1. Open-loop differential mode voltage amplification factor: referred to as open-loop gain for short, which indicates the amplification capability of the operational amplifier itself. It is generally 50 000 to 200 000 times.

2. Input offset voltage: It indicates the degree to which the output voltage deviates from the predetermined value in the static state. Generally 2 10mV (referred to the input terminal).

3, unity gain bandwidth: It means the frequency when the magnification of differential mode voltage drops to 1. Generally around 1MHz.

4, slew rate (also known as slew rate): indicates the adaptability of the operational amplifier to sudden signals. Generally around 0.5V / s.

5. Output voltage and current: indicates the output capability of the op amp. The peak-to-peak output voltage is generally 1 to 3V lower than the power supply voltage, and the short-circuit current is about 25mA.

6. Static power consumption: indicates the power consumption of the op amp under no-signal conditions. When the power supply voltage is ± 15V, the static power bipolar transistor is generally 50-100mW, and the field effect transistor is generally 1mW.

7. Input offset voltage temperature coefficient: It shows the effect of temperature change on offset voltage. Generally 3 to 5 V / ° C (equivalent to the input terminal).

8. Input bias current: indicates the degree to which the input terminal requests current from the outside. The bipolar transistor is generally 80-500nA, and the field-effect transistor is generally 1nA.

9. Input offset current: indicates the difference in current flowing between the two input terminals. Bipolar transistors are generally 20-200nA, and field-effect transistors are generally less than 1nA.

10. Common mode rejection ratio: It means the ratio of the amplifier's amplification factor to the differential mode signal and the amplification factor to the common mode signal. Generally 70 90dB ^[2]

1.Power supply mode of integrated op amp

The integrated op amp has two power terminals + VCC and -VEE, but has different power supply methods. For different power supply modes, the requirements for input signals are different.

(1) Symmetric dual power supply mode

Operational amplifiers are mostly powered in this way. The positive power (+ E) and negative power (-E) relative to the common terminal (ground) are connected to the + VCC and -VEE pins of the op amp, respectively. In this way, the signal source can be directly connected to the input pin of the op amp, and the output voltage of

1.The differential input stage makes the op amp as high as possible.

We should proceed from actual needs, and do not blindly pursue the advanced nature of indicators.

1. If there are no special requirements, try to choose general-purpose and multi-op amps;

2. It should be noted that the parameters given in the manual are obtained under certain specific conditions. If the conditions change, some parameters also need to change.

3. In the experimental stage and occasions with complicated working environment, try to choose the model with over-voltage, over-current and over-heat protection ^[2] .