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14-BIT Analog to Digital Converter

Tue, 10/30/2001 - 9:17am
Analog Devices introduced a 14-bit analog-to-digital converter (ADC) at 105 million samples per second (MSPS). The AD6645 is more than 60 percent faster than its predecessor, released last year by Analog Devices. The new ADC enables multi-carrier software radio architectures in wireless basestations to achieve higher levels of signal quality as well as to keep pace with future air interface standards. Multi-standard, or multi-carrier, software-defined radio provides dramatic cost savings by allowing basestation designers to program different standards in the field rather than developing separate, dedicated receiver platforms applications requiring high dynamic range, such as communications test equipment, satellite receiver ground stations, and broadband wireless basestations.

Two grades of the AD6645 are available, featuring 105 or 80 MSPS sampling rates. The two-tone spurious-free dynamic range (SFDR) is 100 dB and the signal-to-noise ratio (SNR) is 74 dB/70 dB with 70 MHz/200 MHz inputs, respectively. The fast conversion rate of the AD6645 allows for more cost-effective designs for two major reasons. First, it enables intermediate frequency (IF) sampling, which eliminates a down-conversion stage and the associated components. The reduced part count improves the overall reliability of the basestation. Second, it allows designers to reduce costs by using less expensive analog filters.

The AD6645 is a high-speed, high-performance monolithic 14-bit ADC. All necessary functions, such as track-and-hold (T/H) and reference, are included on the chip to provide a complete conversion solution. Its high speed and performance allow for IF sampling up to 200 MHz while maintaining 11.3 ENOB performance. The AD6645 provides CMOS-compatible digital outputs, and is pin-compatible to its predecessor, the AD6644, a 14-bit, 65 MSPS ADC.

The AD6645 is useful in single and multi-channel digital receivers designed for use in wide channel-bandwidth systems such as CDMA and WCDMA. The high bandwidth and high sample rate support a wide range of input IF frequencies, and when used with a decimating digital receiver, such as the AD6624, undesirable harmonics can be placed outside the frequency band of interest.

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