acquisitionZONE Products for the week of December 18, 2006
Texas Instruments Incorporated (TI) introduced two new precision operational amplifiers that combine ultra-low noise with lower power, smaller package size and higher bandwidth than competitive 36-V amplifiers. The OPA211 and OPA827 enable breakthrough performance for test and measurement, instrumentation, imaging, medical, audio and process control applications. These are the first devices developed using TI's groundbreaking BiCom3HV complementary bipolar 36-V silicon germanium (SiGe) process.
"The OPA211 and OPA827 represent a new class of precision amplifiers and demonstrate TI's commitment to the high-voltage industrial market," said Art George, senior vice president of TI's high-performance analog business. "These new amplifiers deliver extremely high accuracy with significant improvements in power consumption, bandwidth and package size characteristics, which will enable next-generation performance in industrial applications."
The OPA211 is a bipolar-input operational amplifier that achieves 1.1
nV/rtHz voltage noise and 80 MHz gain bandwidth product (GBW) with a supply
current of only 3.6 mA. The device provides 100 µV offset voltage,
0.2 µV/degC offset voltage drift and <1 µs settling time
for driving precision analog-to-digital converters in data acquisition systems.
It also offers rail-to-rail output swing, which enhances dynamic range.
analogZONE Says . . .
These are both very interesting op amps being manufactured on TI's complementary bipolar 36-V SiGe process they have named BiCom3HV. But the pair operate very differently. The OPA211 has a bipolar input -- most suitable for low source impedances -- while the OPA827 has a JFET input -- more suitable for higher source impedances.
Both devices can be operated up to ±18 V, allowing for use in the rather neglected (of recent years) industrial market where ±12 V and ±15 V are the norm. This is an important time for those markets as many earlier pieces of equipment have their lifetimes ending and are in line for replacement. The lower supply range for the OPA211 is ±2.25 V and, for the OPA827, ±4 V.
The OPA211 has an input voltage noise of 0.1 µVpp across the range of 0.1 Hz to 10 Hz, and input noise densities of 2.5 nV/rtHz at 10 Hz, 1.6 nV/rtHz at 100 Hz, and 1.1 nV/rtHz at 1 kHz. These are astonishing numbers and are achieved with a standard pin-out on the packages: the data sheet quotes them (and all the other specifications) across the full range of the supply voltages. Likewise, the input current noise density is quoted as 1.5 pA/rtHz. If you were able to keep your source impedance low, this makes the OPA211 achieve the highest SNRs imaginable, driving very high resolution ADCs using very reasonable rail voltages. The same would be the case using the part as a buffer for the ouput from high-performance DACs. The output is rail-to-rail (an industrial application first!) and the input can be taken to within 1.4 V of the positive rail and 1.8 V of the negative rail. The input voltage offset is 100 µV maximum.
The bandwidth of the OPA211 is 80 MHz with a gain of 100 and 58 MHz with unity gain; the slew rate is a typical 27 V/µs and the open-loop voltage gain is 120 dB. All this is achieved with a no-load quiescent of only 3.6 mA while the part can sink or source 30 mA. There is a shutdown pin, but the quiescent current in shutdown is still a TBD specification. THD +N is also not yet quoted.
This is an extremely nice balance of specifications.
The OPA827 behaves differently. At the maximum supply voltage, input noise voltage across the 0.1 Hz to 10 Hz range is still low (but not as low as the OPA211) at 0.4 µVpp, while the input voltage noise density is quoted as 4.5 nV/rtHz at 1 kHz, and higher, with an input current noise density not yet quoted. With the available supply range the higher noise of the input still makes for some astonishing capabilities in ADC driver applications. Neither the input or output is rail-to-rail in this part, where the input can go within 2.5 V of both the positive and negative rails and the output can go within 2.1 V of the positive rail and 2.75 V of the negative rail. The input offset voltage of this JFET input part is 250 µV maximum.
The GBW of the OPA827 is 18 MHz and slew rate is 22 V/µs with an open-loop voltage gain also of 120 dB. The no-load quiescent current is 4.5 mA and the part can also sink or source 30 mA. There is no shutdown, and on this part the THD + N is also still an unknown.
The range of different applications for both these parts -- both of which are laser-trimmable -- is incredible. From data acquisition to medical, instrumentation, audio, ATE, process control and on and on. The higher source impedances are probably going to drive most data acquisition system designs to the OPA827, but the incredibly low noise and rail-to-rail output of the OPA211 are going to be hugely attractive to a lot of designers. The input voltage restrictions on both parts will keep them out of consumer-type products, but those are not the niches these parts were designed to fill. The industrial market is also not nearly as price sensitive and the premiums that TI is demanding will be happily paid in exchange for the performance achieved. The process is the real winner here, long term, and these two first parts will clear the way for a huge number of others. Both are shown in the data sheet as having duals on the horizon -- the OPA2211 and OPA2827 -- and it will be very interesting to see how the noise numbers are, or are not, affected. With this kind of performance designers are going to have to be particularly careful not to throw a chunk of it away with poor layouts or careless simulations. It will be intriguing, also, to see if industrial equipment designers will go for the available DFN packaging for the OPA211, and its dual, in a field where there is still a lot of that good old-fashioned "must be fixable" attitude.
The OPA211 will be available in SO-8 (no enable pin shown in the data sheet), MSOP-8 and a thermally-enhanced DFN-8. The dual OPA2211 will be in MSOP-8 and thermally-enhanced DFN-8, both losing, of course, the enable pin. The OPA827 will be in SO-8 and MSOP-8, while the dual OPA2827 will be in SO-8 and TSSOP-8.
Both the OPA211 and OPA827 are both sampling with production scheduled for Q2 2007. The OPA211 wil be priced at $3.45 and the OPA827 at $5.75, both in 1000-piece lots.
Data
Sheet (OPA211)
Data
Sheet (OPA827)