New Analog-To-Digital Converter Captures Weak Signals In Noisy Environments

Norwood, MA -- Analog Devices, Inc. (ADI) has introduced a high-speed analog-to-digital converter (ADC), the AD9445, which the company says is the first 14-bit, 125-MSPS (mega-samples-per-second) ADC to achieve a spurious-free dynamic range (SFDR) above 80 dBc and a signal-to-noise ratio (SNR) of 72.5 dBfs at input frequencies up to 300 MHz. ADI claims that this performance bests competing solutions by 10 dB and 4 dB, respectively.

A converter with high SFDR can capture weak signals in the frequency band of interest, despite the presence of strong, interfering signals. The SNR characteristics of the AD9445 enable wireless infrastructure equipment designers to improve cellular base station receivers by offering lower overall system noise at higher intermediate frequencies, which translates to expanded cellular coverage and fewer dropped calls. Moreover, the combination of high input frequency and high sampling rate eliminates a frequency down-conversion step before the ADC and eases the analog filtering burden.

"The performance of a converter is measured in many dimensions, and in wireless infrastructure SNR and SFDR are key," said Kevin Kattmann, product line director in the High Speed Converter Group at Analog Devices. "Only by pushing the SNR, SFDR and sample rate of the AD9445 were we able to unlock a simplified analog filter topography that increases overall base station receiver performance while reducing cost, time and complexity."

The high SFDR of the AD9445 ADC expands the dynamic range of wireless base station receivers, while improving quality of service and lowering component count and cost. The AD9445 also achieves an aperture jitter of 60 fs (femto seconds), compared to the 250-fs to 300-fs aperture jitter of competing ADCs, which is critical to maintaining SNR at high input frequencies. Aperture jitter is the sample-to-sample variation in aperture delay and a major contributor to overall system signal degradation.

In addition to delivering greater than 80 dBc SFDR at a 300 MHz input frequency and 85 dBc SFDR at 225 MHz, the AD9445 provides high DC accuracy, with typical differential nonlinearity (DNL) of +/-0.2LSB and integral nonlinearity (INL) of +/-1.0 LSB. The ADC also features a flexible input range up to 3.2 Vp-p, allowing the user to achieve SNR performance as high as 78 dBfs, a full 6 dB better than any ADC of this class, while maintaining the SFDR and IF sampling performance. The AD9445 also has an on-chip reference and track-and-hold, and parallel low-voltage differential signaling (LVDS) outputs to ease the interface to digital down-converters.

The AD9445 is optimized for multi-carrier, multi-mode receivers such as those found in next-generation cellular infrastructure equipment. The device's high-resolution and performance also makes it suitable for antenna array positioning, power amplifier linearization, broadband wireless, radar and infrared imaging, medical imaging, communications instrumentation, and software-defined and cognitive radios.

The AD9445-125 and AD9445-105 ADCs are sampling now in a Pb-free, 100-lead TQFP_EP (Thin Quad Flat Pack Exposed Paddle) with production quantities available in September 2005. The devices are supported by two evaluation boards and a behavioral model that can be used with Analog Devices' ADIsimADC modeling software.

Source: Analog Devices