LMP2021_15 Datasheet, PDF (15/37 Pages) Texas Instruments – LMP202x Zero-Drift, Low-Noise, EMI-Hardened Amplifiers

www.ti.com
7 Detailed Description
LMP2021, LMP2022
SNOSAY9F – SEPTEMBER 2008 – REVISED DECEMBER 2014
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
input voltage noise of only 260 nV_PP at 0.1 Hz to 10 Hz make the LMP202x great choices for high gain
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:
V_OUT = A_OL (IN⁺ - IN^-)
(1)
where A_OL is the open-loop gain of the amplifier, typically around 100dB (100,000x, or 10uV per Volt).
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.
Copyright © 2008–2014, Texas Instruments Incorporated
Product Folder Links: LMP2021 LMP2022
Submit Documentation Feedback
15