10 MHz Bandwidth, 640 MSPS Dual Continuous Time Sigma-Delta Modulator

The AD9267 is a dual continuous time (CT) sigma-delta (Σ-Δ) modulator with -88 dBc of dynamic range over 10 MHz real or 20 MHz complex bandwidth. The combination of high dynamic range, wide bandwidth, and characteristics unique to the continuous time Σ-Δ modulator architecture makes the AD9267 an ideal solution for wireless communication systems.

The AD9267 has a resistive input impedance that significantly relaxes the requirements of the driver amplifier. In addition, a 32× oversampled fifth-order continuous time loop filter attenuates out-of-band signals and aliases, reducing the need for external filters at the input. The low noise figure of 15 dB relaxes the linearity requirements of the front-end signal chain components, and the high dynamic range reduces the need for an automatic gain control (AGC) loop.

A differential input clock controls all internal conversion cycles. An external clock input or the integrated integer-N PLL provides the 640 MHz internal clock needed for the oversampled conti- nuous time Σ-Δ modulator. The digital output data is presented as 4-bit, LVDS at 640 MSPS in twos complement format. A data clock output (DCO) is provided to ensure proper latch timing with receiving logic. Additional digital signal processing may be required on the 4-bit modulator output to remove the out-of-band noise and to reduce the sample rate.

The AD9267 operates on a 1.8 V power supply, consuming 416 mW. The AD9267 is available in a 64-lead LFCSP and is specified over the industrial temperature range (−40°C to +85°C).

Product Highlights

* Continuous time Σ-Δ architecture efficiently achieves high dynamic range and wide bandwidth.

* Passive input structure reduces or eliminates the require- ments for a driver amplifier.

* An oversampling ratio of 32× and high order loop filter provide excellent alias rejection, reducing or eliminating the need for antialiasing filters.

* Operates from a single 1.8 V power supply.

* A standard serial port interface (SPI) supports various product features and functions.

* Features a low pin count, high speed LVDS interface with data output clock.

Applications

* Baseband quadrature receivers: CDMA2000, W-CDMA, multicarrier GSM/EDGE, 802.16x, and LTE

* Quadrature sampling instrumentation

* SNR: 83 dB (85 dBFS) to 10 MHz input * SFDR: −88 dBc to 10 MHz input * Noise figure: 15 dB * Input impedance: 1 kΩ