When you are trying to digitize a modulated RF signal, you have several choices: you can heterodyne the signal down to a lower intermediate frequency (IF) one or even twice, then digitize; you can heterodyne it directly down to baseband (zero-IF); or you can try to digitize it directly at its carrier frequency. The latter offers the potential to eliminate many signal-chain components, but places stringent, difficult demands on the analog/digital converter (ADC).
Attacking this challenge, the ADC12Dxx00RF family of 12-bit converters from National Semiconductor Corp. comprises a pin-compatible family, featuring conversion rates from 1.0 to 3.6 Gsps, while handling signals beyond 2.7 GHz. These specifications make it a fit even for direct RF-sampling of 3G/4G base stations, and an enabler of high-end SDR (software defined radio) designs. Simplifying signal processing, it enables sampling into—and beyond—the 7th Nyquist zone. The converters can be configured for interleaved or dual-channel modes, for I/Q demodulation.
This converters—which the vendor says are the first to achieve direct RF-sampling beyond 2.7 GHz—can eliminate approximately 20 components usually associated with the channel, while reducing overall power consumption and board-space requirements. (They are also footprint-compatible with National's existing ADC12D1x00 and ADC10D1x00 families.)
The five converters being released are:
The ADC12D1800RF, which provides interleavedsingle-channel sampling rates up to 3.6 Gsps, ordual-channel rates up to 1.8 Gsps, with IMD3 of -64 dBc at 2.7 GHz; noise floor -155 dBm/Hz, and 4.4 W dissipation. (More information is available at http://www.national.com/pf/DC/ADC12D1800RF.html.)
The ADC12D1600RF, which provides interleavedsingle-channel sampling rates up to 3.2 Gsps, ordual-channel rates up to 1.6 Gsps, with IMD3 of -70 dBc at 2.7 GHz; noise floor -154.6 dBm/Hz, and 4.0 W dissipation (See http://www.national.com/pf/DC/ADC12D1600RF.html.)
The ADC12D1000RF, which provides interleavedsingle-channel sampling rates up to 2.0 Gsps, or dual-channel rates up to 1.0 Gsps, with IMD3 of -69 dBc at 2.7 GHz; noise floor -154 dBm/Hz, and 3.5 W dissipation. (See http://www.national.com/pf/DC/ADC12D1000RF.html.)
The ADC12D800RF, which provides interleavedsingle-channel sampling rates up to 1.6 Gsps, or dual-channel rates up to 800 Msps, with IMD3 of -71 dBc at 2.7 GHz; noise floor -152.2 dBm/Hz, and 2.5 W dissipation. (See http://www.national.com/pf/DC/ADC12D800RF.html.)
The ADC12D500RF, which provides interleavedsingle-channel sampling rates up to 1.0 Gsps, ordual-channel rates up to 500 Msps, with IMD3 of -69 dBc at 2.7 GHz; noise floor -150.5 dBm/Hz, and 2,0 W dissipation. (See http://www.national.com/pf/DC/ADC12D500RF.html.)
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