Lattice Semiconductor Introduces All-In-One Programmable Filter — Unique Single-Chip Analog IC is In-System Programmable - Lattice Semiconductor ispPAC80 - Product Announcement

Edge: Work-Group Computing Report, March 6, 2000

Lattice Semiconductor Monday announced the newest member of its ispPAC family of Programmable Analog Circuit monolithic ICs, the ispPAC80 in-system programmable filter. The ispPAC80 allows users to derive tens of thousands of different fifth-order precision filters from a single compact IC in a few seconds.

The new product, an all-in-one, single-chip, continuous-time fifth-order filter, incorporates many additional advances to the ispPAC family, such as increased frequency range (up to 500kHz at full-scale amplitude), further improved offset performance, and new features such as a dual configuration memory. This "two-chips-in-one" capability allows the user to swap between two entirely different filter configurations by sending a command through the JTAG or SPI interface. The device instantly assumes the new configuration.

The ispPAC80 joins the ispPAC10 and ispPAC20 products introduced in the fourth quarter of 1999. The earlier products are general-purpose, being capable of solving many different types of analog design problems smoothly. The ispPAC80 device is focused on filtering applications.

"Filters make up a large portion of all designs which use discrete and low-integration analog components," said Andy Robin, VP of New Venture Businesses for Lattice. "It's always been tough to get those filters to work and be manufacturable at small tolerances in a system. But with the ispPAC80 chip, it's a pushbutton breeze."

The ispPAC80 integrates all analog components necessary to easily implement a huge range of 50 kHz -500 kHz Butterworth, Chebychev, Legendre, Elliptical, Gaussian, and Linear Phase low-pass filters. An engineer uses a search engine built into the PAC-Designer software to quickly find the desired filter characteristics, sees the resulting simulation, and downloads the design into the chip. If changes are desired, the chip can be reprogrammed instantly.

Advances in Technology Continuous-time fifth-order filters are very complex functions that have been burdensome and involved for analog designers. In the traditional approach, after multiple laborious calculations trying to choose the right filter type, a designer would then secure the needed components. To be aggressive about the filter's characteristics, the designer would buy high-precision resistors while being subject to the rather loose precision inherent in discrete capacitors. Very likely, precision OpAmps would be needed before and after the R-C filter. With components in hand, a breadboard would be created, which entails solving layout problems typical of the analog world. The resulting design might not deliver the desired results, after all -- and then it's back to the drawing board. Once the design is reasonably final, analog component variability presents further hurdles to be overcome on the way to manufacturability.

By contrast, the Lattice ispPAC technology incorporates all needed analog components on-chip, with thousands of highly precise, selectable values built in. This avoids the nuisance of having to secure the right parts. The essentially transparent ispPAC internal interconnect scheme eliminates the layout problem completely -- the whole filter is in one ispPAC chip. Further, the resistors and capacitors built into an ispPAC device provide much higher overall filter precision than can be achieved with a non-monolithic approach, in addition to the obvious board-space saving integration benefit. Finally, if the user doesn't find the chosen filter to be what they wanted for their application, the ispPAC device's E(2) memory allows it to be reconfigured in an instant without searching for components, without creating a new board layout, and without any filter debug cycles.

Additionally, the ispPAC80 "two-chips-in-one" capability allows the user to swap between two entirely different filter configurations. This on-the-fly reconfiguration effectively doubles the number of saved components in many designs. Useful applications for this capability include "seek-and-acquire" modes, test, and calibration sequences. The device also features a quick-access register to change the gain of the instrumentation input amplifier or to trigger a system offset calibration for critical applications.

The ispPAC80 contains approximately 3,000 individual capacitors, arranged in what looks to the user like just seven programmable capacitors with 9-12-bit resolution. Thus, filter frequencies are never more than 3.5% away from a desired value between 50kHz and 500kHz. Overall, the user has 70 bits of control resulting in trillions of filter responses, all accessible through the simple PAC-Designer software.

What You See Is What You Get The entire ispPAC family is supported by the PAC-Designer software tool, an integrated analog design environment with an easy-to-use GUI. Using the PAC-Designer software at a PC, an engineer selects their filter type and characteristics on-screen. A simulator shows the resulting signals immediately. Since the analog components used to implement the filter, their characteristics, and their interconnect are all on-chip, the designer can now enjoy the incomparable "What You See Is What You Get" benefit of the ispPAC Family - the programmed chip delivers precisely the filter response shown by the simulator.