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.
