Simplification of the sideband suppression & carrier leakage calibration process

Linear Technology Korea (CEO Hong Sa-kwak) announced the launch of a new low-power I/Q modulator (product name: LTC5589).

This product enables battery-powered, high-performance broadband transmitter operation in the 700MHz to 6GHz range. Powered from a 2.7V to 3.6V power supply, the LTC5589 modulator consumes only 29.5mA of current, representing 50% less power consumption compared to other existing solutions. The new modulator provides industry-leading sideband suppression of -50dBc and carrier leakage of -43dBm without the need for calibration.

Sideband and carrier suppression can be further enhanced by using on-chip tuning capabilities via the SPI bus, achieving performance of -60dBc and -60dBm, respectively. Furthermore, this device provides very low output noise of -158.8dBm/Hz, and combined with an OIP3 of 19dBm, it offers excellent transmitter performance.

The LTC5589 supports not only narrowband but also wideband transmitters. Its baseband bandwidth extends up to 92 MHz with ±1 dB gain flatness, and it provides 184 MHz RF bandwidth at 1.8 GHz. Combining low power consumption and robust performance, this device is suitable for a wide range of demanding applications for radio and wireless communications.

These products include broadband modems, femto and picocell broadband wireless access, wireless microphones and portable audio systems, broadband portable field radios, unlicensed band radios, train communication, software-defined radios (SDR), portable RF test equipment, low-power microwave backhaul and repeaters, telemetry radios and satellite modems, etc.

Previous zero-IF modulators suffered from excessive carrier leakage and degraded sideband suppression, resulting in poor Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR) values. Calibration is a tricky process that relies on a digital tuning algorithm in a bandwidth FPGA using an external DAC.

Tuning resolution is generally limited. The LTC5589 provides on-chip tuning capabilities for I-channel and Q-channel phase and amplitude mismatches, affecting sideband suppression. This device also offers DC offset balance adjustment, which affects carrier leakage. With built-in controlled calibration capabilities via a serial port, the LTC5589 simplifies calibration tasks and enables cost-effective implementation.

The gain of the LTC5589 can be set via the on-chip serial port. The coarse gain control is 1 dB/step, and an adjustable fine gain control of 0.1 dB is also provided. The total gain range is –19 dB to 0 dB. If the modulator gain value fluctuates, it can affect the device supply current from 9mA to 39mA, and the device can be configured for lower power consumption with slightly reduced gain and performance depending on the requirements of a specific application. Once configured, the gain is automatically temperature-corrected by enabling the on-chip temperature correction function.

The LTC5589 is available in a 4mm x 4mm plastic QFN package and offers a small solution footprint. The operating temperature range is standardized to –40°C to 105°C. The device provides an enable pin for TDD or burst mode transmitter operation. When disabled, the LTC5589 conserves power by typically consuming 0.6μA of quiescent current. The modulator can be turned on at full quadrature accuracy within 350ns. The LTC5589 is priced at $4.45 per unit in 1,000-piece quantities and is available for mass production.