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AD6643 Dual IF Receiver

Two ADCs are contained in a small, space-saving, 9 mm × 9 mm × 0.85 mm, 64-lead LFCSP package. Pin selectable noise shaping requantizer (NSR) function that allows for improved SNR within a reduced bandwidth of up to 60 MHz at 185 MSPS. LVDS digital output interface configured for low cost FPGA families. Operation from a single 1.8 V supply. Standard serial port interface (SPI) that supports various product features and functions, such as data formatting (offset binary or twos complement), NSR, power-down, test modes, and voltage reference mode. On-chip integer 1-to-8 input clock divider and multichip sync function to support a wide range of clocking schemes and multichannel subsystems.

The AD6643 is an 11-bit, 250MSPS, dual-channel intermediate frequency (IF) receiver specifically designed to support multiantenna systems in telecommunication applications where high dynamic range performance, low power, and small size are desired.

The device consists of two high performance analog-to-digital converters (ADCs) and noise shaping requantizer (NSR) digital blocks. Each ADC consists of a multistage, differential pipelined architecture with integrated output error correction logic. The ADC features a wide bandwidth switched-capacitor sampling network within the first stage of the differential pipeline. An integrated voltage reference eases design considerations. A duty cycle stabilizer (DCS) compensates for variations in the ADC clock duty cycle, allowing the converters to maintain excellent performance.

Each ADC output is connected internally to an NSR block. The integrated NSR circuitry allows for improved SNR performance in a smaller frequency band within the Nyquist bandwidth. The device supports two different output modes selectable via the external MODE pin or the SPI.

With the NSR feature enabled, the outputs of the ADCs are processed such that the AD6643 supports enhanced SNR performance within a limited portion of the Nyquist bandwidth while maintaining an 11-bit output resolution. The NSR block can be programmed to provide a bandwidth of either 22% or 33% of the sample clock. For example, with a sample clock rate of 185 MSPS, the AD6643 can achieve up to 75.5 dBFS SNR for a 40 MHz bandwidth in the 22% mode and up to 73.7 dBFS SNR for a 60 MHz bandwidth in the 33% mode.

With the NSR block disabled, the ADC data is provided directly to the output with a resolution of 11 bits. The AD6643 can achieve up to 66.5 dBFS SNR for the entire Nyquist bandwidth when operated in this mode. This allows the AD6643 to be used in telecommunication applications such as a digital predistortion observation path where wider bandwidths are desired.

After digital signal processing, multiplexed output data is routed into two 11-bit output ports such that the maximum data rate is 500Mbps (DDR). These outputs are set at 1.8 V LVDS and support ANSI-644 levels.

The AD6643 receiver digitizes a wide spectrum of IF frequencies. Each receiver is designed for simultaneous reception of a separate antenna. This IF sampling architecture greatly reduces component cost and complexity compared with traditional analog techniques or less integrated digital methods.

Flexible power-down options allow significant power savings. Programming for device setup and control is accomplished using a 3-wire SPI-compatible serial interface with numerous modes to support board-level system testing.

PRODUCT HIGHLIGHTS

APPLICATIONS

• Communications
• Diversity radio and smart antenna (MIMO) systems
• Multimode digital receivers (3G) WCDMA, LTE, CDMA2000 WiMAX, TD-SCDMA
• I/Q demodulation systems
• General-purpose software radios

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