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Process augments op amp performance

Santa Clara, Calif. — Six operational amplifiers that were built on National Semiconductor Corp.'s new, proprietary VIP50 process technology are said to feature significant improvements in accuracy, low power consumption and voltage noise for industrial, medical and automotive applications.

These improvements, combined with the products' small size, also make them suited for portable applications, the company said.

National's four latest products in this market, the LMV651, LMV791, LPV511 and LPV7215, offer world-class gain bandwidth product performance, according to National Semiconductor. For example, the 12-MHz, unity-gain bandwidth LMV651 amplifier provides 90 percent power savings over major competitive offerings in SOT and SC70 packages. Other products feature sub-1 μA performance and functional operation up to 12 V, as well as nanoamp comparators with 6.6 μs of propagation delay in SC70 packaging.

Expanding its precision amplifier portfolio, National is also introducing the LMP7701 and LMP7711, the first products in a series of next-generation operational amplifiers that offer higher performance, sub-300 μV of input offset with guaranteed input bias of less than 200 fA, and up to 12-V operation.

Precision Amplifiers: Femto Amp Input Current for Accurate Sensor Interfacing

The LMP7711 single amplifier offers low current (50 fA) MOS inputs while still providing low-noise (less than 7 nV/√ Hz) performance, minimizing distortion and signal-conditioning errors. Precision thin-film resistors and well-matched transistor pairs are used to guarantee input offset errors of less than 200 μV, increase common-mode rejection ratio (CMRR) of 95 dB and increase power supply rejection ratio (PSRR) of 100 dB performance, while maintaining a low offset voltage drift of 1 μV/°C over extreme temperatures (-40°C to 125°C).

The LMP7701 precision amplifier operates from 2.7 V to 12 V supply voltages and has rail-to-rail CMOS inputs with low input-bias current (200 fA). Trim and design techniques eliminate the large offset glitch associated with conventional CMOS rail-to-rail input amplifiers, improving the input offset voltage of less than 300 μV across the entire common-mode voltage range (0 V to 12 V). It also employs a patented correction technique to reduce the large temperature coefficient of the offset voltage commonly found in CMOS precision amplifiers. Both products are available in a SOT23 package.

Low-Noise Op Amp With Shutdown

The LMV791 low-noise CMOS input operational amplifier offers 5.8 nV/√ Hz of flat band noise. Its low offset voltage of less than 1.3 mV and low temperature coefficient of less than 3 μV/°C improve overall system accuracy. The 100 dB PSRR and 95 dB CMRR provide the DC performance needed in high-performance applications. A shutdown feature reduces power consumption to less than 1 μA when in idle mode. The LMV791 is available in a six-lead TSOT23 package.

Unparalleled Bandwidth-to-Power Ratio

The LMV651's high-efficiency design provides 90 percent power savings over previous- generation operational amplifiers by consuming only 115 μA while maintaining a 12 MHz unity-gain bandwidth and a low 1/f noise voltage of 17 nV/√ Hz. Its less than 1 mV input offset voltage, 100 dB CMRR and 95 dB PSRR improve the overall DC system accuracy across various input voltages and supply voltages. The LMV651 is offered in an SC70 package.

Ultra-low-power Amplifier and Comparator

The LPV511 micro-power operational amplifier and the LPV7215 micro-power comparator consume less than 900 nA and 600 nA of supply current, respectively. Both products offer rail-to-rail inputs and outputs. The LPV511 is specified for 2.7 V to 12 V operation, while the LPV7215 comparator is operational from 1.8 V up to 5 V. The LPV7215 offers a 6.6 μs propagation delay that quickly detects if a voltage fault condition has occurred, sending a precise output response to a microcontroller or other system diagnostic IC.

The space-saving SC70 package and -40°C to +85°C temperature range make these products suitable for continuously on, battery-powered applications, such as smoke detectors, as well as industrial, telecommunications and automotive applications.

 
 
See related LPV511 (Supply Current vs Supply Voltage graphic

These six new products are designed on the VIP50 process, a silicon-on-insulator BiCMOS process with trimmable, highly-accurate thin-film resistors (see related VIP50 diagram in the “eeProductCenter's Bettyann Liotta Says:” column).

Pricing and Availability

The LMP7711, LMP7701, LPV511, LMV791, LMV651 and LPV7215 are available now. The LMP7711 is priced at $1.55 in 1,000-unit quantities. Click here for additional pricing, samples and data sheets.

National Semiconductor , 1-800-272-9959, www.National.com.

National believes its new VIP50 manufacturing process will raise the bar for bandwidth-to-power ratios found in op amps today — with this process resulting in a huge bandwidth boost and 90 percent savings in current consumption.

The company is rolling out five new operational amplifiers and one comparator that were built using this BiCMOS process. These devices tout high precision and low power as a result of this process, said Huibert Verhoeven, senior design manager for National's low voltage, low power and precision amps. “We are pushing the performance curve relative to precision, speed-to-power and signal-to-noise ratio (SNR) with VIP50,” he said.

National's silicon-on-insulator BiCMOS VIP10 process, which was launched in 2001, was used to produce 50 high-speed amps with speeds reaching into the GHz range for telecom and video applications. The company's previous generation low-voltage low-power BiCMOS process uses slower transistors and is more power hungry. This process was used to manufacture the LMV line of amplifier products.

The new low power, precision amplifiers, which fall in the 50 MHz and below category, are meant to complement National's high-speed amplifiers.

Although the two manufacturing processes sound similar, (VIP50 and VIP10) they are two totally different processes that utilize the same foundation, Verhoeven said.

National went one step further with this BiCMOS process by incorporating the silicon-on-insulator wafer process. Essentially, it's the same technology used to make high-speed amplifiers. “Picture ICs being made on wafers. You only use the top layer to make the circuit and the rest of it is used for mechanical handling. You end up with a thick block of material that takes longer to heat up and requires more power to get to a certain speed,” Verhoeven said.

 
 
See related VIP50 diagram

The silicon-on-insulator process puts a tiny layer of silicon on an oxide-covered wafer. On top of the oxide, National is still using BiCMOS. Although this is considered a common way to make later generation high-speed amps, it's a new way to make low power, precision amps. “We found that reducing the thin layer of silicon made the process very well suited for precision, low power amps,” Verhoeven said.

The newer process is a lot costlier than the traditional process, and the company didn't immediately realize the full benefits of the optimized process, Verhoeven said. “Then we realized we could reduce the current by 10 times, but still maintain the same speed. Normally, you push a silicon-on-insulator BiCMOS process to get the highest speed possible, not to get the lowest current possible. When we instead optimized for low current, we got a 90 percent performance improvement over the previous generation (ours and the competition's),” Verhoeven said.

Previous generation precision, low power amps use quite a bit of power and don't offer the same precision level as the newer devices. The older LMV771 amplifier, for instance, has a 1 mV maximum offset voltage, compared to only a 150 μV maximum for the LMP7711, Verhoeven said.

Typically, the tradeoff for op amps is low current = low speed. “We have the same fundamental tradeoffs as our competitors, but using VIP50, ours is still 10x faster than theirs,” Verhoeven said.

When comparing the older LMV821 with the new LMV651, the LMV651 is more than two times faster but it only uses one quarter of the supply current.

Additionally, the older process was limited in terms of applications with only a 5-V maximum supply voltage, compared to a 12-V supply voltage for the newer devices, which expands the applications to outside the portable arena, Verhoeven said.

The key attributes of the six devices that National is introducing using the VIP50 process are:

The LPV511 op amp and LPV7215 comparator tout excellent speed at a very low current — less than 1 μA. The LPV511 op amp, a 12-V device in an SC70 package offers a rail-to-rail input and output and only draws 880-nA current.

The LMV651 offers 12 MHz of bandwidth for only 110 μ A of supply current.

The LMV791 is a low noise device. “We chose to use a CMOS input to drive the noise down to less than 6 nV at 1 kHz, while guaranteeing an input bias current of less than 0.5 pA,” Verhoeven said.

The LMP7701 and LMP7711 boast really good precision — 150 μV to 200 μV of offset maximum. Both parts use CMOS transistors on the front
to-rail input and output while still enabling 12-V operation.

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