Electronic Design

Complementary-Bipolar CMOS Process Goes Modular

Hoping to expand its portfolio of high-performance analog and mixed-signal ICs, Burr-Brown Corp., Tucson, Ariz., has developed a proprietary complementary-bipolar CMOS (CBC) process for high-speed communications applications. Modular in nature, the CBC is a completely new biCMOS technology that has been under development at Burr-Brown for over two years. Its designers have tailored it to merge precision, high-speed analog functions with high-density digital circuits to deliver new levels in mixed-signal integration for applications like DSL, cable modems, base-station receivers, and fiber optics.

With a 1-µm (drawn) feature size for bipolar transistors and a 0.8-µm density for the CMOS circuits, the CBC is a leading-edge process that offers npn and pnp transistors with cutoff frequencies of 10 and 7 GHz, respectively. It also has a typical Early voltage of 80 V. Plus, it uses a modular approach to add Schottky diodes, JFET transistors, high-performance passives, and submicron CMOS as option modules, besides the core complementary high-speed bipolar devices (see the figure).

The newly developed CBC process provides a high-quality, low-noise JFET transistor that enables superior input stages, says Joel Halbert, design group manager for high-speed signal processing products at Burr-Brown. It also boasts trimmable thin-film resistors and precision capacitors with minimized parasitic effects, as well as excellent linearity and tracking. The linearity offered by the precision resistors and capacitors is a few ppm per volt. For instance, precision capacitors can be linear to 5 ppm/V, with a voltage coefficient of 10 to 50 ppm/V. This translates into significant improvements in noise and distortion. The process also affords additional isolation for high-density CMOS circuits, providing separate tubs wherein circuits can be built in isolation. This is critical in mixed-signal designs, since it minimizes crosstalk and improves the precision and speed of analog circuits.

The result is better precision, higher gain, and faster speed for analog circuits. In essence, the CBC process is crafted to provide a two-fold improvement in dynamic performance and quiescent current, says Michael Steffes, senior strategic engineer at Burr-Brown. Traditionally, he adds, designers had to make several compromises to cut the quiescent current. Making very few compromises, it also now supplies the digital control, glue logic, and interfaces to microprocessors and DSPs. Along with running high-performance analog and mixed-signal circuits on ±5 V, CBC implements a 0- to 5-V CMOS interface, Steffes says.

Having tested the technology on a 200-MHz dual op amp, the company is now readying high-performance amplifiers at low cost. Dual voltage-feedback and dual wideband, high-current output op amps are in the works.

While the voltage-feedback op amp features a high-gain bandwidth product of 200 MHz on only a 5.5-mA/channel quiescent current, the op amp with high output current is tailored for driving xDSL lines. Consuming a low, 9-mA/channel quiescent current, the wideband, high-output current op amp will be able to deliver a 400-mA peak output current.

TAGS: Digital ICs
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