Op Amps Eliminate EMI-Induced Errors in Analog Systems
Portable Design News, Monday August 25, 2008
National Semiconductor Corp. has introduced three new operational amplifiers (op amps) with integrated electromagnetic interference (EMI) filters that maintain the accuracy of analog systems by reducing the effects of radio frequency (RF) interference.
The LMV83x op amps deliver the industry’s highest EMI rejection ratio (EMIRR) of 120 dB, thereby eliminating EMI-induced errors. They also feature 3 MHz unity gain bandwidth while operating on only 240 μA of supply current. This yields a power-to-performance ratio of 80 μA per MHz, which places these devices among National’s PowerWise family of energy-efficient products.
The LMV831 single, LMV832 dual and LMV834 quad EMI-hardened op amps reduce development time and board size by minimizing the need for metal shielding, filters and extra components. They are well-suited for use in phone accessories, medical instruments, precision weigh scales and other industrial electronic equipment that are sensitive to electromagnetic disturbances in noisy environments. For example, an injected RF signal in a weigh scale can result in as much as 1V of output offset, which would diminish a 10-bit analog-to-digital converter’s (ADC’s) resolution (1024 codes) to the equivalent of only 3-bits. Using an LMV83x op amp would only reduce resolution by 0.2-bits. A wide range of applications can benefit from EMI protection, including filters/buffers, photodiode preamp and piezoelectric sensors.
The LMV831 single, LMV832 dual and LMV834 quad op amps feature CMOS inputs, a maximum input offset voltage of 1 mV, a rail-to-rail output stage and an input common-mode voltage range that includes ground. These devices provide a common-mode rejection ratio (CMRR) and a power supply rejection ratio (PSRR) of 93 dB. The LMV83x devices maintain stability for capacitive loads as large as 200 pF and offer a wide temperature range of -40 degrees C to 125 degrees C. The LMV831 is offered in a 5-pin SC70 package, while the LMV832 is offered in an 8-pin MSOP package and the LMV834 is offered in a 14-pin TSSOP package.
The LMV831 is priced at 55 cents each, the LMV832 is 79 cents each, and the LMV834 is priced at $1.10 each in 1,000-unit quantities. Samples of all three EMI-hardened op amps are available now and production quantities will be available in third quarter 2008.
National Semiconductor Corporation, Santa Clara, CA (408) 721-5000 >[http://www.national.com/]
