AD620 Instrumentation Amplifier Instructions for Use

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AD620 Instrumentation Amplifier Instructions for Use [Copy link]

Author: Huang Kai (2002-05-05) , Recommended: Xu Yeliang (2002-05-25) .

AD620 Instrumentation Amplifier Instructions for Use

In general signal amplification applications, only a differential amplifier circuit can usually meet the needs. However, the basic differential amplifier circuit has poor precision, and when changing the amplification gain on the differential amplifier circuit, two resistors must be adjusted, which affects The variables of the overall signal amplification accuracy are even more complex. The instrument amplifier circuit does not have the above shortcomings. This article will first introduce the instrument amplifier circuit, and then explain the usage and application examples of the AD620 instrument amplifier IC .

1. Introduction to AD620 Instrumentation Amplifier

Figure 1 The instrument amplifier circuit is composed of three amplifiers. The resistors R and R _x need to be within the resistance range of the amplifier (1kW ~ 10kW ) . _With a fixed resistor R , we can adjust R ).

(1)

Figure 1. Schematic diagram of instrument amplification circuit

Generally speaking, the above instrumentation amplifiers are available in packaged form. We only need to connect an external resistor (i.e. R _x in equation (1) ) and adjust it to the required amplification according to its unique relationship: Can. The following is an introduction to the use of the AD620 instrumentation amplifier.

Figure 2 shows the pinout of the AD620 instrumentation amplifier. Pins 1 and 8 need to be connected across a resistor to adjust the amplification (the function is the same as R x in equation ( 1 ) ₎ . Pins 4 and 7 need to provide positive and negative equal working voltages. The amplified voltage can be output from pin 6 as the amplified voltage value. Pin 5 is the reference. If it is grounded, the output of pin 6 is the relative voltage to ground. The amplification gain relationship of AD620 is shown in equation (2) and equation (3) . Through these two equations, we can calculate the resistor values used for various gains. .

Figure 2. AD620 pin diagram

(2)

(3)

The basic features of AD620 are high accuracy, ease of use, low noise, and a wide range of applications. Table 1 is an overview of the specifications and features of AD620 .

Table 1. AD620 specification and feature description table

project	Specifications	Remark
gain range	1~1000	Only one resistor is needed to set
Power supply range
Low power consumption	max supply current =1.3mA	Can be powered by batteries, convenient for use in portable equipment
High accuracy	40 ppm maximum nonlinearity; low offset voltage of 50 μ V max.; offset drift of 0.6 μ V/ ℃ max.
low noise	Low input voltage noise of 9nV/ at 1kHz.
Application occasions	ECG measurement and medical equipment, pressure measurement, V/I conversion, data acquisition system ... etc.

2. Introduction to AD620 instrumentation amplifier application example circuit

2.1 Basic signal amplification circuit description and testing

Figure 3 is the AD620 voltage amplification circuit diagram. The resistor R _G must be obtained from equation (3) according to the desired amplification factor . The whole circuit is quite simple. Next, the actual test situation will be introduced.

Figure 3. AD620 amplifier circuit diagram

From formula (3), it can be calculated that the resistor used to amplify 2 times is 49.4k , so we connected the circuit as shown in Figure 4 , and performed voltage amplification on the dry cell (output voltage 1.32V , as shown in Figure 5 ), and finally we obtained the amplified output result as shown in Figure 6 . Because the resistor we used was not controlled to an accurate 49.4kW ( actually 49.6kW ), the output result was not an accurate 2 times the value of 2.64V .

Positive and negative 15V power supply

Figure 4. The actual situation of voltage amplification of dry batteries

Figure 5. Amplification of a dry cell battery with an output voltage of 1.32V

Figure 6. Output result is 2.68V

2.2 AD620 application circuit

AD620 is very suitable for pressure sensing applications, such as blood pressure measurement, bridge circuit signal amplification of general pressure sensors, etc. Figure 7 shows the amplification of the pressure sensing circuit formed by the bridge, and finally converts the analog signal into a digital signal through the ADC .

Figure 7. Pressure sensing circuit example

The AD620 can also be used for ECG measurement. Figure 8 shows the ECG measurement circuit diagram. Due to the low power consumption of the AD620 , only a 3V dry battery can be used in this circuit to drive it. Therefore, the AD620 can be used in many portable type of medical equipment.

Figure 8. ECG measurement circuit

Figure 9 shows the application of AD620 in V/I conversion. Through AD620, we can convert voltage into current. R _G in the figure is also obtained by equation (3) , and the output current is

(4)

Figure 9. V/I conversion circuit

The AD620 is much more convenient to use than the 741 amplifier. In particular, it does not need to consider the applicable range of the resistance. It only needs to find the required resistance R _G according to the relationship . At the same time, its applications are also quite wide, especially those that require high accuracy. In terms of medical treatment, it is suitable for use in various research projects of this laboratory.

References

Principles and Applications of Operational Amplifiers , translated by Zhang Wengong and Jiang Zhaoai, Rulin Books Co., Ltd. , March 1990 . [code language="ASPX"] [/code]

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