Dual A/D converter consumes little power at high speeds

Santa Clara, Calif. — National Semiconductor Corp.'s dual high-performance CMOS analog-to-digital (A/D) converter uses significantly less power than competitive products while providing the Gigahertz speeds necessary for reliable measurements of high-frequency signals.

These high-speed, low-power devices are designed specifically for applications such as digital oscilloscopes, automated test equipment (ATE), base stations, satellites and communications systems requiring direct I/Q down-conversion. As one of the key building blocks in system signal path designs, A/D converters accurately capture real-world analog information and convert it for processing in the digital domain.

The ADC08D1000 digitizes two input signals to 8-bit resolution at sampling rates up to 1 gigasamples per second (GSPS) while consuming 1.6 W from a 1.9-volt nominal supply. By using the fully programmable dual-edge-sampling feature, the product can achieve 2 GSPS sampling from one channel by interleaving the two on-chip converters. Both coarse and fine timing adjustments are available, allowing the sampling clock for each channel to be calibrated independently in 0.1-picosecond increments. A three-wire serial bus controls these adjustments, as well as on-chip functionality, and independent gain and offset fine-tuning for I and Q channels. The ultra-low power requirements of the ADC08D1000 enable designers to eliminate fans or heat sinks, saving board space and reducing system cost.

“National's rapidly expanding portfolio of data converter solutions is enabling dramatic improvements in performance throughout the entire analog signal path,” said Suneil Parulekar, executive vice president, Analog Products Group. “The new ADC08D1000 extends National's range of high-speed products to offer designers a choice of the industry's lowest-power, highest-accuracy products on the market. Our best-in-class A/D converters enable system makers to differentiate their products by offering improved image resolution, enhanced reliability, smaller form-factors and lower power.”

With more than 10 patents pending on its design, National's ADC08D1000 is fabricated using the company's 0.18-micron, high-performance CMOS process technology. The chip features on-chip auto calibration at power-up that enables low power with high performance. In addition, it has unique, performance-enhancing folding/interpolating architecture. Folding reduces the number of comparators, and interpolation greatly reduces the number of front-end amplifiers required, saving power and reducing the load on the input signal. The ADC08D1000 has an ideal pulse response and guarantees “no missing codes” over the full operating temperature range of −40 to 85°C. This enables the product's high level of performance and accuracy. In addition, the ADC08D1000 features a National low-voltage differential signaling (LVDS) interface, which enables reliable transmission of high-speed signals, while maintaining low noise and distortion levels.

The ADC08D1000 is designed with an extremely low bit error rate (BER) of 10-18 . At a 1 GHz sampling rate, the ADC08D1000 achieves 0.25 least significant bits (LSB), differential non-linearity (DNL) and 0.35 LSB integral non-linearity (INL), while maintaining 7.5 effective number of bits (ENOB) from dc up to input frequencies of 500 MHz (Nyquist). Measured crosstalk between the I and Q channels is less than −77 dB. The dual on-chip sample-and-hold amplifiers deliver excellent dynamic performance over a 1.7-GHz full power bandwidth.

With the introduction of the ADC08D1000, National continues to expand its line of high-performance, low-power 8-to-12 bit A/D converter offerings. It joins National's single ADC081000 high-performance CMOS A/D converter. These products will be followed closely by a 500-megasamples per second (MSPS) version and National's 1.5 GSPS device in the first quarter of 2005. All speed grades in National's ultra-high-speed portfolio have the same pin-out, allowing the designer to change the sampling rate without changing the board layout. In addition, National is developing higher-resolution 14- and 16-bit pipeline A/D converters and continuing to build its low-power, general purpose successive approximation register (SAR) A/D converters for broad market applications.

The ADC08D1000, housed in a 128-lead exposed-pad package, is priced at $219 in 1,000-piece volumes. The product is scheduled for full production release in January 2005 and samples will be available at that time.

A data sheet for the ADC08D1000 is available on the web.

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There appears to be very little competition in this particular market segment, which Leonardo Azevedo, the product marketing manager for National's ADC08D1000, chalks up to the analog-customized CMOS process it National uses when manufacturing its A/D converters.

With few players competing, there are significant opportunities for companies like Analog Devices Inc., Texas Instruments Inc., and National Semiconductor Corp., along with several other organizations with intellectual property in this space, said Susie Inouye, senior industry analyst for Databeans Inc., Reno, Nevada.

The proliferation of faster data communications, wireless networking, and medical electronics is driving the market for high-speed A/D converters, which is growing exponentially, Inouye said. Even the supporting industries such as telecom testing, and semiconductor manufacturing, are affected. Databeans estimates that the 50 MSPS A/D converter market is growing at 30% on average, compared to the entire high speed A/D converter market (anything over 1 MSPS, which is estimated to grow at 22% on average). The high speed A/D converter market was estimated in 2003 at $555 million worldwide.

From an applications standpoint, Databeans' research indicated that in the lower resolution high-speed space, applications would include higher volume usage in data communications (fiber channel and Sonet) and then lower volume usage in testing. Wireless networking and medical electronics tend to require 12 bit to 16 bit (and higher) parts. For the ultra, high-speed products, with lower resolutions, these parts would be found in some data communications, but mostly lower volume military, instrumentation, and scientific applications (such as radio astronomy, radar, sonar, etc.)

Before National's high-speed A/D converters came along, similar older products were consuming about 5 W of power, versus National's ADC08D1000, which consumes only 1.6 W of power. Additionally, these older parts required heat sinks and fans to enable the A/D converters to work for any length of time since they would heat up. Besides the fact that designers can save money by eliminating heat sinks and fans, end products can be made much smaller without bulky fans, and years can be added to the product's life expectancy by eliminating heat, Azevedo said.

National made the leap from 200 MHz to 1 to 1.5 GHz last February, when it released the ADC081000, the single-version counterpart of the ADC08D1000. The first product introduced in the Gigahertz range consumed 1.4 W of power. If National just put two of these devices together, they would jointly consume 2.8 W of power. Instead, the company was able to cut power usage nearly in half, and add several features to make it geared specifically for test and measurement equipment makers.

The ADC08D1000 uses a calibrated folding and interpolating architecture that achieves over 7.5 effective bits. The use of folding amplifiers greatly reduces the number of comparators and power consumption. Interpolation reduces the number of front-end amplifiers required, minimizing the load on the input signal and further reducing power requirements. In addition, on-chip calibration reduces the integral nonlinearity (INL) bow often seen with folding architectures. The result is an extremely fast, high performance, low power converter, Azevedo said. “With 8 to 10 bit A/D converters, a folding/interpolating architecture is ideal but can sometimes result in INL bow, which results in a less accurate transfer function curve. To counter this, National's new A/D converter integrates unique internal calibrations that make it ultra-precise and allow us to guarantee no missing codes over the full operating temperature.” In fact, National's BER of 10-18 will enable the chip to run for more than four years continuously before it would give an error reading, he said.

Although samples aren't available until January, designers can design their products now using National's ADC081000 single version A/D converter since it is pin compatible with the ADC08D1000.

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