National Semiconductor’s New Zero-Drift Amplifiers Break the Noise Barrier

The LMP2021 single and LMP2022 dual precision op amps are well-suited for sensor interface applications including load cells and pressure and force sensors used in industrial systems, scientific weigh scales, medical and measurement equipment, and heating, ventilation and air conditioning (HVAC) systems. Both devices are included in National’s recently released WEBENCH® Sensor Designer tool. This new online design tool reduces development time and helps make design easy by guiding engineers through the entire process – from concept, to simulation, to prototyping – of configuring a complete sensor signal path solution in a few keystrokes.

National’s zero-drift amplifiers use a breakthrough noise-shaping technology that employs continuous-correction circuitry to auto zero the input offset error voltage. This enables uninterrupted accuracy over time and temperature, with high common-mode rejection ratio (CMRR) and high power-supply rejection ratio (PSRR). For example, as small amplitude input signals are amplified at higher gains, the op amps’ input voltage noise decreases from a typical 15 nV/sqrt Hz value, measured at a gain of 100 V/V, to as little as 11 nV/sqrt Hz at a gain of 1000 V/V. This key parameter is 50 percent better than the nearest competitor. Additionally, these op amps remove the undesirable 1/f voltage error component in low-frequency applications.

The LMP2021/22 feature integrated electromagnetic interference (EMI) suppression filters and join the recently released LMV83x, LMV85x and LMV86x EMI-hardened op amp families. The LMP2021/22 provides an EMI rejection ratio (EMIRR) of 79 dB to reduce radio frequency (RF) interference from external sources. Additionally, these op amps support 24-bit data acquisition systems and optimally drive National’s new ADC161S626 16-bit analog-to-digital converter (ADC). This ADC provides signal accuracy of +/- 0.003 percent over the -40 degrees C to 85 degrees C temperature range. In high-resolution data acquisition systems, designers commonly scale the output of a sensor to the full-scale input of the ADC to ensure optimum sensitivity.

Key Features – LMP2021/22 Zero-Drift Precision Amplifiers

The LMP2021 single and LMP2022 dual are zero-drift, low-noise, EMI-hardened op amps that have only 0.004 uV per degrees C of input offset voltage drift (TCVos), with a typical Vos of 0.4 uV. Both devices operate across the 2.2V to 5.5V supply voltage range and offer a gain bandwidth (GBW) of 5 MHz while consuming only 1.1 mA of current per channel. The LMP2021/22 op amps offer 160 dB of open loop gain (AVOL), as well as performance exceeding 139 dB for CMRR and 130 dB for PSRR. Both devices operate across the extended temperature range of -40 degrees C to 125 degrees C. The LMP2021 is supplied in 5-pin SOT23 and 8-pin SOIC packages, and the LMP2022 is supplied in 8-pin SOIC and 8-pin MSOP packages.