National Semi’s speedy ADC

National Semi’s speedy ADC

ADC enables fundamental architecture changes in a variety of applications

The 12-bit ADC12D1800 A/D converter from National Semiconductor offers a sampling speed of 3.6 Gsamples/s, which at the time of introduction (May 22, 2010) was said to be 3.6 times faster than the closest competitor. That is what made it a Product of the Year winner for our publication. However, there was more to it.

National had two main goals for the product. The first was to maintain and extend National’s leadership in gigasamples per second (GSPS) analog-to-digital converters (ADCs) by releasing the industry’s fastest 12-bit ADC by a factor of several times. The second was to enable fundamental architecture changes in a variety of applications by enabling truly wideband software-defined radios (SDRs), thereby introducing the GSPS ADCs to many new markets.

A wideband SDR approach allows systems that process multiple channels to be greatly simplified by collapsing all channels into a single signal path. The approach also allows systems that process very-high-input-frequency signals with multiple frequency conversion stages to be simplified by sampling at RF or much higher IF. Although National already offered a large portfolio of GSPS ADCs, the ADC12D1800 was the first GSPS ADC to provide sufficient dynamic performance to allow the deployment of such wideband SDRs in applications including military, communications, industrial, and consumer.

The ADC12D1800 High-Speed Signal Path team was presented with the Electronic Products (EP) Product of the Year trophy. Pictured from left to right: Product Marketing Engineer Scott Kulchycki, EP Magazine editor Jim Harrison, Product Engineer Andrew Glenny, Engineering Program Manager Carlos Hinojosa, Marketing Director Jon Baldwin, Applications Engineers Jim Brinkhurst and Marjorie Plisch, Product Engineer Ryan Hashimoto and Test Development Engineer Linton Park.

Overcoming challenges

The biggest technical challenge was achieving the conversion speed of dual 1.8 GSPS (or single 3.6 GSPS) for a 12-bit ADC in 180-nm CMOS. This challenge was addressed by using a rigorous methodology, simulating the database at the top level over process, voltage, and temperature corners, with layout parasitics included to expose any weakness in the high-speed paths.

Another challenge of the ADC12D1800 and all of National’s GSPS ADCs is that they are complex systems, requiring significant resources and long-term commitment for successful release. The ADC12D1800 is the newest and highest-performance product in National’s family of GSPS ADCs; the product is the latest result of many years of investment and focus by the GSPS ADC development team and by National Semiconductor management.

Christina Nickolas