6 GHz low power direct conversion I/Q modulator

May 31, 2016 // By Graham Prophet
LTC5589 is a low power I/Q modulator that simplifies sideband and carrier suppression calibration, and which enables battery-powered, high performance broadband transmitters operating in the range from 700MHz to 6GHz.

Powered by a single 2.7V to 3.6V supply, the LTC5589 modulator draws 29.5 mA current, 50% lower power consumption than other solutions. The new modulator exhibits sideband suppression performance of -50 dBc and carrier leakage of -43 dBm typical without calibration. Sideband and carrier suppression can be further improved by using the on-chip tuning capabilities via the SPI bus, to better than -60 dBc and -60 dBm, respectively. It has a very low output noise floor of -158.8 dBm/Hz, combined with OIP3 of 19 dBm, resulting in superior transmitter performance.

The LTC5589 supports narrowband as well as wideband transmitters. Its baseband bandwidth extends to 92 MHz with ±1 dB gain flatness, providing 184 MHz RF bandwidth at 1.8 GHz.

Prior zero-IF modulators, Linear asserts, exhibit excessive carrier leakage and poor sideband suppression, resulting in poor Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR). Calibration is challenging and relies on digital tuning algorithms in the baseband FPGA using external DACs. Tuning resolution is typically limited. The LTC5589 provides on-chip tuning capability of the I-channel and Q-channel phase and amplitude mismatch, which affect sideband suppression. The device also has DC offset balance adjustment, which affects carrier leakage. With built-in serial port controlled calibration capability, the LTC5589 simplifies calibration and is cost-effective to implement.