Phone

    00852-6915 1330

AD620 Instrument Amplifier: Principle, Application

  • Contents

I Introduction

Here, you can learn about the AD620 instrument amplifier circuit. Besides, you can also browse AD620 main features, working principles, and applications. This blog generally discusses the following 3 basic questions: 1. What is an instrumentation amplifier; 2. How does it work; 3. How and where to use it.

AD620

Figure 1. AD620

Catalog

I Introduction

II Description

III AD620 Technical Indicators

IV AD620 Working Principle

V AD620 Application

VI Conclusion

FAQ

Ordering & Quantity

II Description

Operational amplifiers have evolved over the decades and as a result, there is a wide variety of them. They can be easily categorized according to their application requirements. The main categories include general-purpose, low-voltage, low-power, high-speed, and high-precision types. In recent years, applications such as consumer electronics, communication, and networking have been developing continuously. And these constantly developing industries also put forward new technical requirements for op-amp products.

AD620 instrument amplifier is the product of AD company. Due to its super β technology, AD620 has the following characteristics:

  • 1.3mA Maximum Working Current
  • 5μV Input Offset Voltage
  • 1μV/℃ Input Offset Drift Maximum
  • 93dB Common Mode Rejection Ratio
  • Adjustable Gain Range
  • Easy to Adjust and Low Noise.

And why can AD620  become an industry-standard high-performance, low-cost instrumentation amplifier? That's because the core of AD620  is a three-stage op-amp circuit, which has a high common-mode rejection ratio, good temperature stability, wide amplification band, and low noise. And it has the characteristics of high accuracy, easy use, and low noise. so this is also the reason why AD620 can be so popular.

III AD620 Technical Indicators

The main technical indicators of AD620 are as follows:

Bandwidth 800MHz
Output power 2.4mW
Power gain 120dB
Working voltage ±15V
Static power consumption 0.48mW
Inoltage ≤60μV
Conversion rate 1.2V/μS
Package form DIP8
Operating temperature range -55℃~+125℃

IV AD620 Working Principle

The functional structure of the AD620 amplifier is shown in Fig. 2.

ad620 functional block diagram

  Figure 2. AD620 Functional Block Diagram

Do you know what the characteristics of this amplifier are? The answer is: differential input, a single-ended output. The voltage gain can be determined by a resistor RG. The gains are adjustable, which solves the problem of connecting the subsequent load to the ground. Besides, A1 and A2 form a differential input and a differential output with in-phase high input impedance and undertake all gain amplification tasks. Because the circuit structure is symmetrical, which means when the gain changes, the input impedance does not change.

The feedback resistance Rl=R2=24.7k. The common-mode gain, offset, drift, and other errors of the amplifiers A1 and A2 are mutually compensated. The gain of the latter stage A3 is 1, which has a higher common-mode rejection ratio and anti-interference ability.

AD620 is a monolithic integrated amplifier. And it is developed on the basis of the improvement of the traditional three-op amplifier combination. As shown in Figure 2, the input transistors Q1 and Q2 provide the only bipolar differential input. Due to the internal ultra-β processing, its input offset current is 10 times lower than the general case. Through the feedback of the Q1-A1-R1 loop and the Q2-A2-R2 loop, the integrated pole current of Q1 and Q2 is kept constant. So the input voltage is equivalent to the two ends of the external resistor RG.

The differential amplification factor from input to A1/A2 output is G=(R1+R2)/RG+1. The unity gain subtractor composed of A3 eliminates any common-mode components. Thereby, it produces a single-channel output related to the potential of the REF pin.

ad620

Figure 3. AD620

So what about RG?

The value of RG also determines the transconductance of the previous stage op-amp. When RG decreases, the magnification increases. When RG decreases, the transconductance to the input transistor gradually increases. This has the following two obvious advantages:

  • First, the increase in the amplification factor increases the open-loop gain. Thereby reducing the gain-bandwidth product and increasing the frequency response;
  • Second, it is mainly determined by the input transistor collector current and base resistance.

By accurately correcting the value of the internal gain resistors R1 and R2 to 24.7kΨ, we can make the operational amplifier gain (derived by calculation) accurately determined by RG: G=49.4kΨ/RG+1 or RG=49.4kΨ/(G- 1)

ad620 circuit structure diagram

  Figure 4. AD620 Circuit Structure Diagram

RG is the external gain adjustment. To meet the required amplification factor, we can connect this high-precision resistance between pin 1 and 8. By using the amplifier AD620.  the gain error can be less than 0.01%, and the non-linearity is less than 0.002%. From the application point of view, AD620 is particularly suitable for applications. Such as sensor interface, ECG monitor, precision voltage current conversion, and other applications. If we analyze the circuit technology performance, we will a deeper understanding of AD620,  That is, AD620 is actually a low-power, high-precision instrument, broadband integrated operational amplifier.

V AD620 Application

Instrumentation amplifiers are sometimes misunderstood by people. Here, we need to point out 2 ideas:

  • First, not all amplifiers used for instrumentation are instrumentation amplifiers;
  • Second, all instrumentation amplifiers are by no means only used for instrumentation. Instrumentation amplifiers are used in many fields. From motor control to data acquisition and automotive systems.

The instrumentation amplifier is a closed-loop gain unit. And with a differential input and single-ended output relative to the reference end. In most cases, the impedance of the two input ends of the instrumentation amplifier is balanced. The resistance is very high, and its typical value is ≥109Ψ. The input bias current is also very low, typically 1nA to 50nA. Like the operational amplifier, its output impedance is very low, usually only a few milliohms in the low-frequency range. The closed-loop gain of an operational amplifier is determined by the external resistance. The external resistance is connected between its inverting input and output.

There are differences between the instrument amplifier and the amplifier. The instrument amplifier uses an internal feedback resistor network, which is isolated from its signal input. To apply input signals to the two differential input terminals of the instrumentation amplifier. The gain can either be preset internally or set by the user. Through a pin connected to an internal or external gain resistor, which is also isolated from the signal input terminal. Figure 5 shows a block diagram of a differential amplifier.

differential amplifier IC

Figure 5. Differential Amplifier IC

This type of IC is a special-purpose instrumentation amplifier. And it usually consists of a subtractor amplifier followed by an output buffer (perhaps one-stage gain). The four resistors used for the subtractor are usually inside the IC, so they can be precisely matched to achieve a higher CMR. Many differential amplifiers are suitable for applications. Where the common-mode voltage and signal voltage may easily exceed the supply voltage. These differential amplifiers usually use high-value input resistors to attenuate the signal.

Generally speaking, instrumentation amplifiers and differential amplifiers are used in the following ranges:

 

  •  Data Acquisition

The main purpose of the instrumentation amplifier is to amplify the weak signal output by the sensor in a noisy environment. Amplification of signals from pressure sensors or temperature sensors is common. Common bridge applications include strain force and weight measurement.

 

  • Medical Instruments

Instrumentation amplifiers are widely used in medical equipment. Such as electrocardiographs and electroencephalographs, blood pressure monitors, and defibrillators. The differential amplifier of monitoring and control electronics can be used to monitor the voltage and current in the system and trigger the alarm system when the normal value is exceeded. Because differential amplifiers have the ability to suppress high common-mode voltages, they are often used in such applications.

electrocardiograph

Figure 6. Electrocardiograph

 

  • Software Programmable Applications

To allow software to control the hardware system, we can turn to instrumentation amplifiers. Instrumentation amplifiers can be used on chips with software programmable resistors.

 

  • Audio Applications

Because instrumentation amplifiers have high CMR, they are used for audio (e.g. microphone preamplifiers) to extract weak signals in noisy environments. Also,it can be used to minimize the offset caused by ground loops Voltage and noise.

 

  • High-speed Signal Conditioning

Due to the increased speed and accuracy requirements of today's video data acquisition systems, the demand for broadband instrumentation amplifiers is increasing. Especially in the field of  CCD  imaging equipment that requires offset correction and input buffering.

In this field, double correction sampling technology is usually used to correct the  CCD image. Generally, use two sample-and-hold amplifiers to monitor the image and reference level, and send the signal voltage to an instrumentation amplifier to provide a DC correction output.

CCD cameraFigure 7. CCD Camera

 

  • Video Applications

High-speed instrumentation amplifiers are used in many video and cable radio frequency (RF) systems to amplify or process high-frequency signals.

 

  • Power Control Applications

Instrumentation amplifiers can also monitor the motor (monitoring and controlling the motor's speed, torque, etc.) by measuring the motor's voltage, current, and the phase relationship of the three-phase  AC  motor. The differential amplifier is used when the input signal voltage exceeds the power supply voltage.

VI Concusion

Generally speaking, high-speed operational amplifiers are mainly used in communication equipment, video systems, and test and measurement instruments. Advanced applications in test and measurement, communications, medical, imaging and other fields are the main driving forces to improve amplifier performance; DSL and consumer video applications are its largest markets.


FAQ

  • What is AD620?

AD620 is a low-cost, high-precision instrumentation amplifier. It only requires an external resistor to set the gain. The gain range is 1 to 10,000.

  • Can I change AD620 to AD623 when making MCU products?

Both AD620 and AD623 are single instrumentation amplifiers, and the pin arrangement is exactly the same.

The main difference is: AD620 must use positive and negative power supplies, AD623 can be a positive and negative power supply or a single power supply.

If the original board is AD620, you can replace it with 623; if the original board is AD623, you may not be able to replace it with 620 (it depends on whether the power supply of the original board circuit is dual power supply or single power supply).

After replacing AD620 and AD623 in single-chip products, the program can work normally without modification.

  • What is the difference between AD620BR and AD620AN?

Their packages are different.

  • What is the output resistance of AD620? How to adjust it?

AD620 is a kind of low power consumption instrument amplifier, its output resistance is about 10K, this is the inherent characteristic of this chip, generally it is difficult to adjust.

If you have requirements for output resistance, you can generally use an external circuit to solve it.

  • Is AD620 a positive phase amplification or a reverse phase amplification?

AD620 is an instrument amplifier, the output voltage is [(Vin+)-(Vin-)]*gain.

If the desired signal is (Vin+)-(Vin-), the gain is positive, which is equivalent to positive amplification.

Conversely, if the desired signal is (Vin-)-(Vin+), the gain is equivalent to negative, which is equivalent to reverse amplification.

  • What is an instrumentation amplifier?

Instrumentation amplifier, an improvement of the differential amplifier, has an input buffer, does not require input impedance matching, so that the amplifier is suitable for measurement and electronic instruments

  • What is the core of AD620?

A three-stage op-amp circuit

  • What are the characteristics of AD620?

Differential input, a single-ended output.

  • What types of systems are instrumentation amplifiers used in?

Data acquisition and automotive systems.

  • What is the instrumentation amplifier?

Closed-loop gain unit

  • What type of amplifier does AD620 IC consist of?

Subtractor amplifier

 

Kynix

Kynix was founded in 2008, specializing in the electronic components distribution business. We adhere to honesty and ethics as our business philosophy and have gradually established an excellent reputation and credibility in our international business. With the accurate quotation, excellent credit, reasonable price, reliable quality, fast delivery, and authentic service, we have won the praise of the majority of customers.

Join our mailing list!

Be the first to know about new products, special offers, and more.

Leave a Reply

We'd love to hear from you! Feel free to share your thoughts and comments below. Rest assured, your email address will remain private.

Name *
Email *
Captcha *
Rating:

Kynix

  • How to purchase

  • Order
  • Search & Inquiry
  • Shipping & Tracking
  • Payment Methods
  • Contact Us

  • Tel: 00852-6915 1330
  • Email: info@kynix.com
  • Follow Us

authentication