The LTC5589 from Linear Technology is a low power direct quadrature modulator designed for low power wireless applications from 700 MHz to 6 GHz that enables direct modulation of differential baseband I and Q signals on an RF carrier. Single side-band modulation or side-band suppressed upconversion can be achieved by applying 90° phase-shifted signals to the I and Q inputs. The I/Q baseband input ports can be either AC or DC coupled to a source with a common mode voltage level of about 1.4V. The SPI interface controls the supply current, modulator gain, and allows adjustments of I and Q gain and phase imbalance to optimize the LO carrier feedthrough and side-band suppression. The LO port can be driven with sine wave or square wave LO drive.
An on-chip thermometer can be activated to compensate for gain-temperature variations. More accurate temperature measurements can be made using an on-chip diode. In addition, a continuous analog gain control (VCTRL) pin can be used for fast power control. It requires a single 2.7 V to 3.6 V supply and draws only 29.5 mA current. It has -50 dBc sideband suppression and -43 dBm carrier leakage without calibration. With on-chip calibration resources, performance can be further improved to –60dBc (Sideband Suppression) and –65dBm (Carrier Leakage). Moreover the device has an excellent noise floor of –157 dBm/Hz at 30 MHz with an OIP3 of 19 dBm. It is available in a 24-Lead 4 × 4 mm Plastic QFN Package and is ideal for military radios, software defined radios and wireless microphones.
