ROHM: CMOS op-amp delivers leading-class low noise

ROHM announces the availability of a CMOS op-amp optimized for applications requiring high-accuracy sensing, such as accelerometers used in sonar systems, and optical sensors that handle ultra-small signals.

Op-amps are configured at the rear stage to amplify the analog sensor output, but because sensor signals are so weak it is necessary to implement noise countermeasures to ensure high-accuracy transmission. In response, ROHM developed a high noise tolerant op-amp for the automotive market utilizing a vertically integrated production system that leverages original analog design technologies and processes. ROHM has introduced an op-amp that delivers the industry’s best performance against external noise optimized for consumer devices and industrial equipment.

The LMR1802G-LB, developed utilizing ROHM’s analog technology covering circuit design, processes, and layout, reduces input equivalent noise voltage density by half (2.9nV/√Hz at 1kHz, 7.8nV/√Hz at 10Hz) compared to conventional products, significantly improving the detection performance of sensor signals. In addition, best-in-class phase margin (68°) and capacitive load tolerance (500pF) provide excellent stability (difficult to oscillate, easy to handle). This enables accurate amplification of voltages in the order of µV, ensuring support for applications requiring high-precision sensing.

This latest product combines ROHM’s superior analog technology covering circuit design (new circuit at the differential input stage), layout, and processes (optimized for low noise) to achieve ultra-low-noise. The input equivalent noise voltage density of 2.0nV/√Hz at 1kHz and 7.8nV/√Hz at 10Hz are approximately half that of products on the market, ensuring superior low-noise performance. Introducing a new circuit at the differential input stage allowed ROHM to achieve industry-low noise along with a class-leading phase margin of 68° and capacitive load tolerance of 500pF. This doubles the detection capability of sensor signals over conventional solutions, enabling accurate amplification of voltages on the order of µV, improving performance with sensors that demand higher precision.

In terms of op-amp configuration, the output voltage should be 0V when the input is 0V, but an offset voltage is often generated as an error. Also, if the sensor’s output impedance is high the sensor output voltage will be affected if the input bias current of the op-amp is large. Consequently, these two error factors must be made as small as possible to ensure optimal performance.

The LMR1802G-LB offers an input offset voltage of 450µV and input bias current of only 0.5pA (4x and 2x less than conventional products, respectively), providing high accuracy amplification.


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