LF398MX/NOPB

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LF398MX/NOPB Application Field and Working Principle

The LF398MX/NOPB, commonly referred to as an instrumentation amplifier (IA), is part of the linear product family of Texas Instruments and is widely used in industrial and commercial applications where high-performance instrumentation amplifiers are required. An IA is a type of amplifier specifically designed for precision measurements in the range of millivolts, particularly for measurements in low-level signals in a variety of applications. The LF398MX/NOPB is a pin-selectable version that supports single and dual supply operation.

What is an Instrumentation Amplifier?

An IA is a device that amplifies signals while providing high common-mode rejection. IA’s allow to measure small signals in the presence of large common-mode signals, which makes them well-suited for industrial and process controls, production test and related applications. They are also used in sensing applications such as strain and pressure. Furthermore, they can be used for real-time biometric applications, such as blood pressure, electrocardiograms, and electroencephalograms.

What is LF398MX/NOPB?

The LF398MX/NOPB is an instrumentation amplifier (IA) integrated circuit from Texas Instruments. It is a dual operational amplifier that provides a high common-mode rejection ratio (CMRR) of 83 dB, high input impedance and low noise. It is fully differential and features a high level frequency response. The device offers pin selectable gain settings of 5, 10, 20, and 40, and a low offset voltage and offset voltage drift. Furthermore, the device can be operated from a single or dual supplies of +2.7V to +34V, and a wide range of frequencies from DC to 500kHz. With its wide range of features, the LF398MX/NOPB offers excellent performance in industrial and medical applications.

Working Principle

The instrumentation amplifiers have the ability to measure small signals with the presence of large common-mode signals. The LF398MX/NOPB operates in differential mode, where the input signals, these being Vin− and Vin+ respectively, are measured with respect to each other. Two 3-state selectors are used to select the gain of the IA. There is also an adjustable offset voltage which allows the user to adjust the output voltage to account for small variations in the input signals. The output voltage is given by:

The LF398MX/NOPB also has a high common-mode rejection ratio (CMRR) of 83 dB, which allows it to reject any high common-mode signal noise and provide an output that accurately represent the input signal. This high CMRR is provided by two differential amplifier stages, one for the inverting and one for non-inverting inputs. The first differential amplifier stage consists of two FETs connected to the non-inverting and inverting inputs from the external signal, and a current source connected to their common drain. The current source applies a constant current to the FETs, which maintains their gain and keeps the common-mode rejection ratio constant.

The second differential amplifier stage is where the high common mode rejection is achieved. It includes two resistors connected to the non-inverting and inverting inputs, which have different values in order to provide the required gain. In addition to this, the LF398MX/NOPB has an adjustable offset voltage that allows the user to adjust the output voltage to account for small variations in the input signals.

Conclusion

The LF398MX/NOPB is an incredibly useful device for any application that requires a high-performance instrumentation amplifier. The device offers excellent performance, with a high common-mode rejection ratio, low noise, adjustable gain, and adjustable offset voltage. In addition, it can be operated from a single or dual supplies, making it a versatile and cost-effective solution for many industrial and medical applications.

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