AD6659

The AD6659 is a mixed-signal, dual-channel IF receiver supporting radio topologies requiring two receiver signal paths, such as in main/diversity or direct conversion. This communications systems processor consists of two high performance analog-to-digital converters (ADCs) and noise shaping requantizer (NSR) digital blocks. It is designed to support various commu-nications applications where high dynamic range performance and small size are desired.

The high dynamic range ADC core features a multistage differential pipelined architecture with integrated output error correction logic. Each ADC features a wide bandwidth switch capacitor sampling network within the first stage of the differential pipeline. An integrated voltage reference eases design considerations.

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 region. The device supports two different output modes selectable via the serial port interface (SPI).

With the NSR feature enabled, the outputs of the ADCs are processed such that the AD6659 supports enhanced SNR performance within a limited region of the Nyquist bandwidth while maintaining a 12-bit output resolution. The NSR block is programmed to provide a bandwidth of 20% of the sample clock. For example, with a sample clock rate of 80 MSPS, the AD6659 can achieve up to 81.5 dBFS SNR for a 16 MHz bandwidth at 9.7 MHz AIN.

With the NSR block disabled, the ADC data is provided directly to the output with an output resolution of 12 bits. The AD6659 can achieve up to 72 dBFS SNR for the entire Nyquist bandwidth when operated in this mode.

After digital processing, output data is routed into two 12-bit output ports that support 1.8 V or 3.3 V CMOS levels. The AD6659 receiver digitizes a wide spectrum of IF frequencies. Each receiver is designed for simultaneous reception of the main and diversity channel. This IF sampling architecture greatly reduces component cost and complexity compared with traditional analog techniques or less integrated digital methods.

The AD6659 also incorporates an optional integrated dc offset correction and quadrature error correction (QEC) block that corrects for gain and phase mismatch between the two channels. This functional block proves invaluable in complex signal processing applications such as direct conversion receivers.

The ADC contains several features designed to maximize flexibility and minimize system cost, such as programmable clock and data alignment and programmable digital test pattern generation. The available digital test patterns include built-in deterministic and pseudorandom patterns, along with custom user-defined test patterns entered via the serial port interface (SPI).

A differential clock input controls all internal conversion cycles. An optional duty cycle stabilizer (DCS) compensates for wide variations in the clock duty cycle while maintaining excellent overall ADC performance.

The digital output data is presented in offset binary, gray code, or twos complement format. A data clock output (DCO) is provided for each ADC channel to ensure proper latch timing with receiving logic. Both 1.8 V and 3.3 V CMOS levels are supported, and output data can be multiplexed onto a single output bus.

The AD6659 is available in a 64-lead, RoHS-compliant LFCSP, and it is specified over the industrial temperature range (−40°C to +85°C).

Applications

• Communications
• Diversity radio systems
• Multimode digital receivers 

3G, W-CDMA, LTE, CDMA2000, TD-SCDMA, MC-GSM

• I/Q demodulation systems
• Smart antenna systems
• Battery-powered instruments
• General-purpose software radios