The LTC5599 is a direct conversion I/Q modulator designed for low power wireless applications that enable 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 degree 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 optimization of the LO carrier feedthrough and side-band suppression, with sine wave or square wave LO drive. A fixed LC network on the LO and RF ports covers a continuous 90MHz to 1300MHz operation. 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.