Datasheet

LMP2021, LMP2022
www.ti.com SNOSAY9E –SEPTEMBER 2008–REVISED MARGH 2013
APPLICATION INFORMATION
LMP2021/LMP2022
The LMP2021/LMP2022 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
LMP2021/LMP2022 offer on chip EMI suppression circuitry which greatly enhances the performance of these
precision amplifiers in the presence of radio frequency signals and other disturbances.
The LMP2021/LMP2022 utilize proprietary techniques to measure and continuously correct the input offset error
voltage. The LMP2021/LMP2022 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 LMP2021/LMP2022 is less than
11 nV/√Hz at a voltage gain of 1000 V/V and has no flicker noise component. This makes the
LMP2021/LMP2022 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 LMP2021/LMP2022 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 LMP2021/LMP2022 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 LMP2021/LMP2022 have an extended supply voltage range of 2.2V to 5.5V, 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.
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 LMP2021/LMP2022 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.
Twisted pair cabling and the active front-end’s common-mode rejection provide immunity against low frequency
noise (i.e. 60 Hz or 50 Hz mains) but are ineffective against RF interference. Figure 50 displays this. Even a few
centimeters of PCB trace and wiring for sensors located close to the amplifier can pick up significant 1 GHz RF.
The integrated EMI filters of LMP2021/LMP2022 reduce or eliminate external shielding and filtering requirements,
thereby increasing system robustness. A larger EMIRR means more rejection of the RF interference. For more
information on EMIRR, please refer to AN-1698 (Literature Number SNOA497).
INPUT VOLTAGE NOISE
The input voltage noise density of the LMP2021/LMP2022 has no 1/f corner, and its value depends on the
feedback network used. This feature of the LMP2021/LMP2022 differentiates this family from other products
currently available from other vendors. In particular, the input voltage noise density decreases as the closed loop
voltage gain of the LMP2021/LMP2022 increases. The input voltage noise of the LMP2021/LMP2022 is less than
11 nV/√Hz when the closed loop voltage gain of the op amp is 1000. Higher voltage gains are required for
smaller input signals. When the input signal is smaller, a lower input voltage noise is quite advantageous and
increases the signal to noise ratio.
Figure 39 shows the input voltage noise of the LMP2021/LMP2022 as the closed loop gain increases.
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