High linearity I/Q demodulator improves image rejection, says ADI

Analog Devices has released the LTC5594, a wideband, high linearity true zero-IF (ZIF) demodulator with 1GHz instantaneous I and Q 1dB bandwidth. The demodulator is capable of 37dB image rejection typical.

Using the on-chip serial port, the device can be tuned to achieve an image rejection of better than 60dB, by allowing correction of the I and Q phase and amplitude imbalance. This feature is claimed to ease calibration while significantly improving receiver performance and reducing the FPGA resources needed to null the residual image. The LTC5594 has integrated baseband amplifiers with adjustable gain, providing a maximum power conversion gain of 9.2dB at 5.8GHz, while delivering 37dBm output IP3 performance.

The RF input has an integrated wideband balun transformer, allowing single-ended operation with 50-Ohm matching from 500MHz to 9GHz. The same input can be matched at lower frequencies from 300 to 500MHz by changing one external matching component value. Its high level of integration results in minimum external components and small solution size.

The on-chip serial port can be used to set all the calibration. Image rejection, linearity performance including IP2 (2nd order intercept), HD2 (2nd order harmonic distortion), HD3 (3rd order harmonic distortion), and IIP3 can be optimised. The output DC offset voltage can be nulled via the serial port to allow DC coupling to the ADC for true ZIF operation, adds Analog Devices. Once calibrated at room temperature, these performance metrics are stable at cold or hot, up to the rated temperature extremes from –40 to +105 degree C case.

The LTC5594 is suitable for 5G microwave wireless infrastructure platforms that require 1GHz or more bandwidth, and dynamic range performance to support the high order modulation and gigabit data rates required. The demodulator can also be used in broadband microwave point-to-point backhaul, high performance GPS systems, satellite communications, aircraft avionics, RF test equipment and radar systems. Its linearity and image rejection performance are described as compelling for DPD (digital pre-distortion) receiver applications.

The LTC5594 is offered in a 32-lead, 5.0 x 5.0mm plastic QFN package. The demodulator is powered from a single 5V supply, drawing a nominal 470mA current. The baseband amplifiers can be selectively disabled, so the demodulator can run on 250mA current. An enable pin allows an external controller to shut down the device. When disabled, the device typically draws 20-microA supply current. Samples and production quantities are available immediately.


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