Various applications of differential amplifiers

Various Applications of Differential Amplifiers

1. Overview

Currently, there are many types of operational amplifiers on the market, commonly including general-purpose, precision op-amps, high input impedance types, high-speed types, low-power types, and high-voltage high-power types. Each type of op-amp has its unique characteristics. Engineers should choose the type of op-amp based on the application scenario. Among them, differential amplifiers are often used in signal acquisition and transmission due to their high precision and strong noise resistance.

2. Application Fields

1.Situations where the input voltage range is lower than the supply voltage

When conducting pressure/magnetic/and temperature measurements using a Wheatstone bridge for signal acquisition and processing, because the input voltage range is lower than the supply voltage, an instrumentation amplifier can be used for signal acquisition and processing.

Instrumentation amplifiers are favored in applications involving weak signal acquisition and sensor signal amplification due to their high common-mode rejection ratio, high input impedance, low noise, low linear error, low offset drift, and adjustable gain. Hangjing Company has completed the research and design of instrumentation amplifiers such as HJG620HJG620, HJG826, HJG118, HJG826, HJG128, HJG826, HJG333, HJG826, and, HJ52301.HJ52301. These devices have been widely applied and can completely replace imported devices such as. AD620, HJG826. INA826, HJG826. INA118, HJG826. INA128, HJG826. INA333., HJ52301. MII-52301 devices are completely replaced by domestic production.

Figure 1 Application of Instrumentation Amplifier

REF

The input at this terminal can adjust the output signal bias; however,the input signal at this terminal must have low output impedance with current sourcing and sinking capabilities to ensure that output errors are minimized. This means using an op-amp for buffering at this terminal or using a reference voltage source for setting terminal voltages can guarantee small output errors. In contrast,using resistor divider methods or LDOs will increase output errors and reduce acquisition accuracy.the input signal at this terminal must have low output impedance with current sourcing and sinking capabilities to ensure that output errors are minimized. This means using an op-amp for buffering at this terminal or using a reference voltage source for setting terminal voltages can guarantee small output errors. In contrast,The operating range of an instrumentation amplifier depends on common-mode voltage, gain,the input signal at this terminal must have low output impedance with current sourcing and sinking capabilities to ensure that output errors are minimized. This means using an op-amp for buffering at this terminal or using a reference voltage source for setting terminal voltages can guarantee small output errors. In contrast,and pin voltages; thus,the input signal at this terminal must have low output impedance with current sourcing and sinking capabilities to ensure that output errors are minimized. This means using an op-amp for buffering at this terminal or using a reference voltage source for setting terminal voltages can guarantee small output errors. In contrast,the size of common-mode inputs affects device performance characteristics—this relationship is known as the diamond plot for instrumentation amplifiers. This characteristic influenced by common-mode voltage must be particularly noted when instrumentation amplifiers operate under single-supply conditions.2Typical diamond plot for single-supply operation of instrumentation amplifier

As seen from the above figure, when setting a large output for a single-supply operating instrumentation amplifier,the input signal at this terminal must have low output impedance with current sourcing and sinking capabilities to ensure that output errors are minimized. This means using an op-amp for buffering at this terminal or using a reference voltage source for setting terminal voltages can guarantee small output errors. In contrast,its input common-mode voltage range becomes very narrow at typical supply voltages; therefore,

Figure if one wishes to acquire smaller voltage signals at the input terminal,a new bias voltage must be added at this terminal to widen its input common-mode voltage range.

From the above figure, it can be seen that when a single power supply instrument amplifier is set to a larger output, its input common mode voltage range will be very narrow at the general power supply voltage. At this point, if you want to collect a smaller voltage signal at the input terminal, you must have low output impact with current sourcing and sinking capabilities to ensure that output errors are minimized This means using an op-amp for buffering at this terminal or using a reference voltage source for setting terminal voltages can guarantee small output errors. In contrast, Adding a new bias voltage to the terminal can widen the range of input common mode voltage accordingly.

2. Common GND system with input voltage range greater than power supply voltage

When the input voltage is greater than the power supply voltage, the above-mentioned instrument amplifier cannot be used for signal acquisition and processing, and a differential amplifier should be selected for operation.

Figure 3 Typical principle block diagram of differential amplifier

Differential amplifiers first proportionally reduce the input voltage, and then internally reset the gain network to obtain a fixed gain. Through this electrical connection structure, the input voltage range of the entire device can be amplified to exceed the power supply voltage. When designing the peripheral resistors of differential amplifiers, low-temperature drift thin film materials are used to obtain excellent temperature characteristics, which reduces the impact of device output errors on temperature changes and maintains high-precision input signal acquisition and processing. Moreover, due to the high input resistance of differential amplifiers, the devices are less susceptible to the effects of white noise and input ripple. Therefore, without the need for power isolation, there is no need to set up redundant filtering and isolation networks. Differential amplifiers can replace isolation amplifiers, greatly reducing the overall cost of the system.

Hangjing Company has currently completed HJ133A, The research and design of differential amplifiers such as HJG826HJINA148 and HJ629 can be applied to the imported model INA133, HJG826INA148 and AD629 differential amplifiers are completely replaced by domestic production. And this type of product has already received a large number of purchases and practical applications from customers.

3.The input voltage range is greater than that of the power supply in an ungrounded system (galvanic isolation）

Due to the lack of a common ground,  the measured signal is often parasitic in complex common-mode and differential-mode interference, accompanied by common-mode transient interference.

Figure 4 Typical principle block diagram of an isolation amplifier

An isolation amplifier is a special measurement amplification circuit that has no direct electrical coupling between its input, output, and various power circuits. That is, there is no common ground terminal during signal transmission, and there is electrical isolation between the device's input and output. It is an integrated circuit capable of transmitting, isolating, amplifying, and processing various information signals.Under the working conditions of a complex electromagnetic environmentto performisolation amplification's output function.

Due to its internal design featuring electrical isolation, isolation amplifiers generally have strong common-mode transient suppression capabilities. When there are instantaneous large voltage changes on the input signal, the ultra-high common-mode transient suppression capability ensures that such changes do not affect the device's output. This means that even if destructive voltage changes occur at the input end, the device's performance will not be damaged.The measurement errors caused result in higher measurement accuracy. Isolation amplifiers have the ability to collect and amplify weak signals with higher precision.

Hangjing Company has currently completed HJ278, The research and design of isolation amplifiers such as HJ52301 and HJ5B40 series can completely replace the imported ADI-5B40 isolation amplifier with domestic production. The isolation withstand voltage between the input and output of HJ5B40 series can reach 4242V. This type of product has received a large number of purchases and practical applications from customers.