Demonstration circuit 831 is an I/Q modulator featuring the LT5518. The LTâ5518 is a 1.6GHz to 2.4GHz direct I/Q modulator designed for high performance wireless applications, including wireless infrastructure. It may also be configured as an image reject upconverting mixer, by applying 90° phaseshifted signals to the I and Q inputs. The 5518’s high-speed, internally matched LO amplifier drives two double-balanced mixer cores, allowing the use of a low power, single-ended LO source. The 5518 allows direct modulation of an RF signal using differential baseband I and Q signals. It supports GSM, EDGE, CDMA, CDMA2000, W-CDMA, 64-QAM, OFDM and other modulation formats. The 5518’s I/Q baseband inputs consist of voltage-tocurrent converters that in turn drive double-balanced mixers. The outputs of these mixers are summed and applied to an on-chip RF transformer, which converts the differential mixer signals to a 50W single-ended output. The four balanced I and Q base-band input ports are intended for DC coupling from a source with a common-mode voltage level of about 2.1V. The differential input impedance of the baseband inputs is approximately 2.9KW, making them ideally suited for voltage-drive applications. The 5518’s LO path consists of an LO buffer with single-ended input, and precision quadrature generators which produce the LO drive for the mixers. Demonstration circuit 831 is designed for an RF output frequency range from 1.5GHz to 2.4GHz.