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Low-noise op amps offer rail-to-rail outputs and 3V operation

Two new families of high-speed operational amplifiers from Linear Technology set new low power and low noise performance benchmarks. These devices consume only 50% as much power as competitive devices and deliver ultra low noise performance, rail-to-rail outputs and fully specified 3.3V operation. The LT6230/1/2 and LT6233/4/5 amplifiers combine features ideal for designing active filters and driving A/D converters in instrumentation, communications and medical equipment.

The LT6233/4/5 are single/dual/quad ultra low noise, rail-to-rail output, unity gain stable op amps that feature 1.9nV/rtHz noise voltage and draw only 1.15mA of supply current per amplifier. These amplifiers combine very low noise and supply current with a 60MHz gain bandwidth product, a 17V/us slew rate and are optimized for low supply voltage signal conditioning systems. The LT6233-10 is a 375MHz single amplifier optimized for higher gain applications.
The LT6230/1/2 are higher speed versions that offer 215MHz gain bandwidth and an even lower voltage noise of 1.1nV/rtHz, yet still draw a best-in-class 3.4mA of supply current per amplifier. The decompensated version for closed-loop gains greater than 10 (LT6230-10) offers a gain bandwidth product of 1.45GHz and 320V/us slew rate.
“Portable instrumentation and high channel count applications that demand high speed, low noise amplification and filtering will immediately reap the benefits of the dramatically reduced current draw”, comments Erik Soule, product marketing manager for LTC's Signal Conditioning Products. “Power is saved across the board – even the shutdown current has been reduced to less than a microamp. These new amplifiers really push the power vs. noise curve off the chart”.

All amplifiers have an output that swings within 50mV of either supply rail to maximize the signal dynamic range in low supply applications. Input offset voltage is trimmed to less than 350uV — exceptional for a high-speed amplifier. The devices are fully specified on 3.3V, 5V and ±5V supplies, and are guaranteed over the commercial (0°C to 70°C) and industrial (-40°C to +85°C) temperature ranges.

Summary of Features:
Ultra Low Noise Voltage:
1.1nV/rtHz (LT6230/1/2)
1.9nV/rtHz (LT6233/4/5)
Low Supply Current:
3.4mA (LT6230/1/2)
1.1mA (LT6233/4/5)
Low Offset Voltage: 350uV Max
High Speed: 60MHz to 1.45GHz versions
Wide Supply Range: 3V to 12.6V
Output Swings Rail-to-Rail
Common Mode Rejection Ratio: 115dB
Output Current: 30mA
Operating Temperature Range: -40°C to 85°C
Shutdown to 10uA Max (singles)
Tiny ThinSOT, DFN, SO-8 and SSOP packages

Linear Technology Corporation 1630 McCarthy Boulevard Milpitas, CA 95035-7417. Tel: 408-432-1900and 1-800-4-LINEAR (for literature only. http://www.linear.com

These six op amps are two groups of amplifiers from the same family. The 6230, 1, and 2 are a single, dual and quad amp, respectively and the 6233, 4, and 5 are also single, dual and quad amps. The difference between them is a trade-off of speed versus power and noise. However, they are unique for low-noise, high-speed amplifiers because they have very low power consumption compared to similar competitive products.

Other amplifiers at 1mA don't come close to the noise levels of these components, unless you move to a higher current of approximately 3 mA. How does the company attain such low numbers? They say it's trickery and cleverness, or said another way, good design trade offs, and certainly the process architecture helps. These are bi-CMOS amps and they use a clever new topology on the input stage and are rail-to-rail output, but not rail-to-rail on the input, and that's one of the tricks that saves power and keeps noise low. The other design that saves power is the shut down mode, which isn't uncommon but what is uncommon is that it has a guaranteed maximum of only 10 uA shutdown current and typically it is around 1uA. Many competitors' products have a shutdown in the 100 uA or higher range.

The 6230, 1, 2 are better suited for the communications and medical applications. They are better suited because they have lower noise but they trade off more power with less speed. If you need to save every micro amp then you would want to go with the low power amplifier, but you get it at the expense of a little bit more noise.

The competition for these six op amps is the usual cast of characters including TI, and ADI but these offer a lower noise floor than most. These op amps also have decent DC precision. Many high-speed amplifiers have 1 mV or even several millivolts of offset and this family has a guaranteed maximum of 350 mV, which is relevant if you're DC coupling. They are ideal devices for portable equipment products, including portable medical and industrial because it provides speed as well as low power and a small package.

The single versions (LT6230/3) offer an enable pin and are available in the 6-lead SOT-23 package. The duals (LT6231/4) are offered in the 8-pin SO package with industry standard pinouts. For compact layouts, the duals are also available in a tiny 3 x 3 x 0.8mm dual, flat leadless package (DFN). The quads (LT6232/5) are available in the space-saving 16-pin SSOP package. All versions are now in full production, with pricing from $1.25 in 1k quantities.

LT6230/1/2 data sheet

LT6233/4/5 data sheet

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