Precision Op Amps | National Semiconductor — Low Noise Amplifiers, Low Offset Voltage, Auto-Zero, Low Input Bias Current, Low Power Home->Amplifiers

Precision Op Amps

Select by Offset and Noise (Click Part Number)

LMV651 LMC6081 LMC6061 LMV791 LF412 LMV841 LMP8100 LMP7715 LMP7701 LMV771 LMP2231 LMP2021 LMP7731 LMV851 LMP7721 LMV641 LMV651 LMC6081 LMC662 LF412 LMV791 LMP7715/6 LMV841 LMP7701 LMV771 LMP2021 LM8261 LMH6618 LMP7731 LMH6624 LMV851 LMP7721 LMV641

You can also view these parts in a parametric table

 

Select by Operating Voltage and Supply Current (Click Part Number)

LMC662 LMV651 LMP7715 LMV791 LMP7701 LMV771 LMC6081 LM358 LF412 LMV841 LMP8100 LM8261 LMC6061 LMP2231 LMH6618 LMP2021 LMP7731 LMV851 LMP7721 LMH6624 LMV641 LMV651 LMP8100/LMP2021/LMV851 LMP7721/LMV771 LMP7715/LMP7721/LMV791 LMP7731 LF412 LMC6081/LMC662 LMV841 LM8261 LMV641 LMH6618/LMP7701 LMH6624

You can also view these parts in a parametric table

 

Offset and Noise  

Offset and noise of amplifiers limit (to a first order) the accuracy and resolution of a precision system. Although today's intelligent systems can calibrate out DC system errors such as the amplifier's offset, this improvement in baseline accuracy comes at the expense of dynamic range (resolution). Noise, on the other hand, cannot be calibrated out of a signal path and thus directly degrades the system's resolution or sensitivity. The high gain required in front-end stages dictates careful selection of amplifiers for their input-referred voltage and current properties.

The "By Lowest Noise" graph serves as a starting point for the designer to quickly choose an amplifier based on flat-band noise density, the dominant contributor in most applications. For clarity, only a selection of op amps suitable for precision applications is shown in the graphs below. Singles, duals, and quads may be found by clicking on the part.

 

Peak-to-peak voltage noise at the output can be estimated by 6.6 x voltage noise density x rt-bandwidth x gain. Thus, the larger the amplification, the more noise density matters for high resolution systems. Low noise amplifiers are also critical for processing very small signals.

Current noise is converted to voltage noise by the feedback network. In photodiode and other applications relying on high transimpedance gain, low current noise op-amps such as LMC662 and LMC6081 are preferred, even at the expense of higher input voltage noise densities. For instance, a 1M-ohm transimpedance translates 10 fA/rt-Hz current noise into equivalent 10 nV/rt-Hz voltage noise.

On the other hand, low valued resistors in the feedback path allow for higher current noise op amps such as LMH6624 and LMP7731 to be used to create the absolutely lowest noise front-ends when power consumption is a lesser consideration. However, the LMP7731 has a 1/f noise corner in the single Hz range (5 decades lower than the  LMH6624), making it more appropriate for the majority of precision sensing applications.

  

Amplifiers with lower Vos and Ib allow for more of the output range to be allocated to the signal, thereby improving system resolution. To aid the system designer with bounded error budgets, National guarantees the maximum Vos and Ib through rigorous testing in production.

Input offset voltage considerations
For preamplifer with gain of 500, a +-1mV offset translates to +-500mV at its output. This amount represents 33% of a 3V signal path. Thus when system dynamic range is important, the first step in picking an amplifier is to choose one with low offset voltage.

Input bias current considerations
Large resistor values are often employed in today's distributed sensing and portable systems to conserve power. These impedances in the feedback network convert an op amp’s input bias currents into offset voltages, and same concerns of the preceding paragraphs apply. 1uA of Ib translates to 1mV of effective Vos with 1K-ohm equivalent impedances. Thus the system designer should also favor amplifiers with low input bias current.

 

Some highlights:

  • LMP2021 achieves best-in-class offset using zero-drift technology. It is a member of National's EMI-Hardened EMIRR family.
  • LMV851 offers an excellent balance between noise, offset, bandwidth, and power. It is a member of National's EMIRR family.
  • LMV641 and LMV651 represent the best noise performance under 200uA supply current.
  • LMP2231 is the lowest power low-offset op amp from National. Consuming just 16uW, it can run for 2 years continuously from a coin cell.
  • LMP7711 has enable/disable in a 6pin SOT-23 and comes in a decompensated version (LMP7717) and 5pin SOT-23 (LMP7715)
  • LMP7701 also comes in a decompensated version, LMP7707.

 

Operating Voltage and Supply Current  

Historically, low noise has been associated with amplifiers requiring high supply voltages. With the introduction of National's proprietary VIP50 process, low noise became available at lower operating voltages as well. Coupled with low supply currents, the LMP and LMV families enable a new class of portable precision.

Low supply currents are critical for applications powered either by a battery or from energy harvesting. The "By Operating Voltage" and "By Supply Current" graphs offer the design engineer a broad portfolio from which to choose the lowest noise op amp for any power budget.

For clarity, only a selection of op amps suitable for precision applications is shown on the selection graphs on this page. Singles are shown on the graph, but duals and quads may be found by clicking on the part in the graph and checking the "Also Recommended" field on the product page.

 

Precision Amplifiers by End Market

Precision is a summation of various DC and AC parameters (e.g. low noise, low offset voltage, low input bias current and other application dependent parameters) and National optimizes these requirements for a wide variety of precision applications. The tables below highlight some of National’s industry-leading precision amplifier products by end application.  Many National Op Amps are tested at three temperatures to ensure consistent performance to specification.

 

Automotive Precision Op Amps

Automotive applications, such as crash detection, active noise cancellation, and navigation, require low offset voltage, low input bias current, and low offset voltage drift at a high voltage supply range. National offers an increasing number of AEC-Q100-compliant devices.  National also has the only current sense operational amplifiers which have tested performance over temperature. National provides the latest solutions making automobiles more efficient, safer, and greener.

 

  Vmin Vmax Vos (max) TCVos Ib Rail-to-Rail Features
LMP7707 2.7 V 12 V 0.2 mV 1 µV/°C 0.2 pA Input/Output Sensor interface, current sensing (ECU and other motor control) applications
LMP8270 4.75 V 5.5 V 1 mV 6 µV/°C 20 pA Output Current sense with fixed gain of 20 to drive an ADC to full scale, 100% tri-temp tested

 

Industrial Precision Op Amps

Industrial applications, such as sensing & detection, weigh scales, pressure monitoring, and motor control, require adjustable gain and low gain error.  Reliability, efficiency and low power consumption are key factors that make National’s precision amplifiers a great choice for industrial needs.

 

  Vmin Vmax Vos (max) TCVos Gain Gain Error (max) Rail-to-Rail Features
LMP8100 2.7 V 5.5 V 250 µV 1.5 µV/°C 1 V/V to 16 V/V 0.03% Input/Output Precision Gain Block for industrial instrumentation and Built-In Test Equipment (BITE)
LMP2021 2.2 V 5.5 V 5 µV 0.004 µV/°C 160 dB   Input/Output Excellent 11nV/vHz at a gain of 1000V/V for load, force, and pressure sensor applications. This zero drift op amp has no 1/f flicker noise component.

 

Consumer/Portable Precision Op Amps

Consumer applications, such as notebook PCs, Bluetooth headsets, and portable media players, require low power consumption.  EMI-hardened amplifiers resist interference from mobile phones and other wireless devices while maintaining accurate operation.  With National’s PowerWise products, sound, display, and power-efficiency are enhanced in consumer and portable electronics.

 

  Vmin Vmax EMIRR Is Vos (max) TCVos (max) Ib (max) Features
LMV831 2.7 V 5.5 V 120 dB 0.24 mA 1 mV 1.5 µV/°C 1 pA Low power and EMI-hardened
LMV851 2.7 V 5.5 V 89 dB 0.52 mA 1 mV 2 µV/°C 10 pA Low power and EMI-hardened

 

Medical Precision Op Amps

Medical applications, such as blood pressure monitors, dialysis machines, and portable medical instruments, require low noise, low offset voltage, high CMRR, and rail-to-rail input and output.  National’s high performance precision products offer the latest solutions for accurate and reliable medical applications.

 

  Vmin Vmax Vos (max) CMRR (min) Noise Features
LMP7731 1.8 V 5.5 V 500 µV 105 dB 3.3 nV/vHz Low 3.3nV/vHz noise at 3Hz. Ideal for precision, low noise, low voltage applications.
LMP2231 1.6 V 5.5 V 150 µV 81 dB 60 nV/vHz Ideal for portable instrumentation

 

Instrumentation Precision Op Amps

Instrumentation applications, such as data acquisition, digital storage scopes and spectrum analyzers require low offset voltage, high CMRR and high PSRR.  National offers an extensive portfolio of amplifiers for metrology applications that meet instrumentation standards, including electrometer amplifiers, amplifiers for transimpedance circuits, chopper amplifiers and auto-zero amplifiers.

 

  Vmin Vmax Vos (max) GBP CMRR (min) PSRR (min) Rail-to-Rail Features
LMP2015 1.8 V 5.5 V 50 µV 3 MHz 100 dB 95 dB Input/Output Auto zero. Precision and long term stability. No 1/f noise.
LMP7701 2.7 V 12 V 200 µV 2.5 MHz 88 dB 86 dB Input/Output CMOS input stage and wide supply voltage range

 

Useful Links

Sensing & Detection Application Diagrams

Automotive Application Diagrams