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LMP2021, LMP2022

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SNOSAY9G – SEPTEMBER 2008 – REVISED FEBRUARY 2016

Product Folder Links: LMP2021 LMP2022

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Copyright © 2008–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LMP202x are single and dual precision operational amplifiers with ultra low offset voltage, ultra low offset

voltage drift, and very low input voltage noise with no 1/f and extended supply voltage range. The LMP202x offer

on chip EMI suppression circuitry which greatly enhances the performance of these precision amplifiers in the

presence of radio frequency signals and other high frequency disturbances.

The LMP202x utilize proprietary auto zero techniques to measure and continuously correct the input offset error

voltage. The LMP202x have a DC input offset voltage with a maximum value of ±5

μV and an input offset voltage

drift maximum value of 0.02 µV/°C. The input voltage noise of the LMP202x is less than 11 nV/

√Hz at a voltage

gain of 1000 V/V and has no flicker noise component. This makes the LMP202x ideal for high accuracy, low

frequency applications where lots of amplification is needed and the input signal has a very small amplitude.

The proprietary input offset correction circuitry enables the LMP202x to have superior CMRR and PSRR

performances. The combination of an open loop voltage gain of 160 dB, CMRR of 142 dB, PSRR of 130 dB,

along with the ultra low input offset voltage of only

−0.4 µV, input offset voltage drift of only −0.004 µV/°C, and

transducer amplifiers, ADC buffer amplifiers, DAC I-V conversion, and other applications requiring precision and

long-term stability. Other features are rail-to-rail output, low supply current of 1.1 mA per amplifier, and a gain-

bandwidth product of 5 MHz.

The LMP202x have an extended supply voltage range of 2.2 V to 5.5 V, making them ideal for battery operated

portable applications. The LMP2021 is offered in 5-pin SOT-23 and 8-pin SOIC packages. The LMP2022 is

offered in 8-pin VSSOP and 8-Pin SOIC packages.

7.2 Functional Block Diagram

7.3 Feature Description

The amplifier's differential inputs consist of a non-inverting input (+IN) and an inverting input (–IN). The amplifier

amplifies only the difference in voltage between the two inputs, which is called the differential input voltage. The

output voltage of the op-amp Vout is given by Equation 1:

(1)

7.4 Device Functional Modes

7.4.1 EMI Suppression

The near-ubiquity of cellular, Bluetooth, and Wi-Fi signals and the rapid rise of sensing systems incorporating

wireless radios make electromagnetic interference (EMI) an evermore important design consideration for

precision signal paths. Though RF signals lie outside the op amp band, RF carrier switching can modulate the

DC offset of the op amp. Also some common RF modulation schemes can induce down-converted components.

The added DC offset and the induced signals are amplified with the signal of interest and thus corrupt the

measurement. The LMP202x use on chip filters to reject these unwanted RF signals at the inputs and power

supply pins; thereby preserving the integrity of the precision signal path.