Analysis of Development and Application Trend of Instrumentation Amplifier

With the rapid development of electronic technology, operational amplifier circuits have also been widely used. As a precision differential voltage amplifier, application scenarios of instrumentation amplifiers in the field of electronic technology are also increasingly rich.

The instrumentation amplifier is a high-gain, dc-coupled amplifier with differential input, single-ended output, high input impedance, and high common-mode rejection ratio. It is suitable for various applications such as pressure or temperature measurement. Its main role includes signal amplification and impedance adaptation. By using a differential small signal superimposed on a large common-mode signal, the instrumentation amplifier can remove the common-mode signal while simultaneously amplifying the differential signal. The key parameter is the common-mode rejection ratio. This performance can be used to measure the ratio of differential gain to common-mode attenuation.

In many cases, the instrumentation amplifier has reference input pins. Increasing the voltage on the reference pin raises the output signal by the same voltage. This makes it simple and accurate to adjust the output of the instrumentation amplifier to the input level required by the ADC, allowing the ADC's full input range to be used while increasing the resolution. In the case of high common-mode signals, another advantage is the excellent common-mode rejection ratio and high accuracy.

However, when design engineers use them, they often experience improper use. Specifically, although modern instrumentation amplifiers have excellent common-mode rejection CMRs, designers must limit the total mode voltage and signal voltage to avoid saturation of the amplifier's internal input buffer. However, design engineers often overlook this requirement.

Common application problems are caused by the following factors: driving the reference end of the instrumentation amplifier with a high-impedance source; operating the instrumentation amplifier circuit with a low supply voltage with a high gain; coupling the input end of the instrumentation amplifier with AC. However, it does not provide a return path for DC to ground; use mismatched RC input coupling elements.

Different topologies that meet different needs

The internal architecture of the instrumentation amplifier varies, depending on the final application target and intended use of the instrumentation amplifier. Each architecture has its own advantages and disadvantages compared to other architectures. For example, traditional three-op-amp instrumentation amplifiers limit the common-mode voltage range and are therefore not suitable for ground-sensing applications. And its common mode rejection ratio (CMRR) is limited by resistor matching requirements.

On the other hand, the current-feedback topology provides a CMRR that is unmatched with resistors. It can have ground sense without the need to add a charge pump that can generate a lot of noise. The current feedback topology combining auto-zeroing and chopping techniques has many advantages in applications that require accurate measurements.

Instrumentation Amplifier Quick Start

The instrumentation amplifier is a dead-loop gain circuit block with differential inputs and single-ended outputs. Instrumentation amplifiers also typically have a reference input to allow the user to level-shift the output voltage up or down. The user can also set the gain by one or more internal or external resistors.

Instrumentation Amplifier vs. Operational Amplifier

For many applications, the CMR characteristic is very important to extract a weak signal from noise, hum or DC offset voltage background. Both operational amplifiers and instrumentation amplifiers have some CMR characteristics. However, the instrumentation amplifier can prevent common-mode signals from appearing at the output of the amplifier. While operational amplifiers also have CMRs, common-mode voltages typically have a unity gain that is transmitted along with the signal to the output.

Most instrumentation amplifiers use three op amps in two stages: a preamplifier consisting of two op amps followed by a differential amplifier. Preamplifiers provide high input impedance, low noise, and gain. The differential amplifier rejects common-mode noise and can also provide some additional gain when needed.

Since its invention, instrumentation amplifiers have undergone a long period of development, beginning with traditional instrumentation amplifiers with two op amps and three op amps, or with a simple differential differential amplifier (DDA). They have different topologies for meeting a wide range of needs from a variety of different application areas.

The first ADI company developed a monolithically integrated instrumentation amplifier. Taking the AD620 as an example, the absolute value calibration allows the user to calibrate the gain with only one resistor and has an accuracy of 0.15 % at G = 100. The monolithic structure and laser wafer trimming technology closely match the components in the circuit and guarantee the inherent high performance of the circuit.

The traditional method of powering instrumentation amplifiers has long been to use dual or bipolar power supplies, which has the obvious advantage of allowing positive and negative input swings and output swings. With the development of component technologies, single-supply operation has become an increasingly useful feature of modern instrumentation amplifiers. Many data acquisition systems now use low-voltage single-supply power supplies.

After many years of research and development, the instrumentation amplifier has formed a variety of features, such as: high common mode rejection ratio, high input impedance. Low Noise, Low Linearity Error, Low Offset Voltage and Offset Voltage Drift, Low Input Bias Current and Offset Current Error, Abundant Bandwidth, With “Check” and “Reference” Sides, This is an Important Standard for Our Instrumentation Amplifiers And basis.

At the same time, with the use of low voltage in applications and data converters to digitize the signal, CMOS technology has made great progress in the field of instrumentation amplifiers. Instrumentation amplifiers based on CMOS technology have unparalleled advantages over equivalent bipolar and JFET instrumentation amplifiers.

Nowadays, with the development of science and technology, instrumentation amplifiers are widely used in various markets such as motor control, thermocouple and bridge sensors to current sensing and medical instrumentation applications such as ECG and EEG.

According to Databeans statistics, the amplifier market has exceeded 2.5 billion U.S. dollars in 2008, and the global market is expected to grow at an annual rate of 8%. Looking at the signal chain of the semiconductor industry, analog signals such as temperature, pressure, humidity, speed, flow, and sound in the real world must undergo digital processing, including a wide variety of data converters and a wide variety of digital signals. Processor and indispensable power management chip. Among them, the amplifier is basically at the forefront of the signal chain and performs the processing of analog signals. As one of the important branches, the development of instrumentation amplifier industry is very spacious!