DC945A

Demonstration circuit 945 is an I/Q modulator featuring the LT®5572. The LT5572 is a 1.5GHz to 2.5GHz 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° phase shifted signals to the I and Q inputs. A high-speed, internally matched LO amplifier drives two double-balanced mixer cores, allowing the use of a low power, single-ended LO source. It allows direct modulation of an RF signal using differential baseband I and Q signals. The LT5572 supports GSM, EDGE, CDMA, CDMA2000, W-CDMA, 64-QAM, OFDM and other modulation formats. The I/Q baseband inputs consist of voltage-to-current 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 50 ohm single-ended output.

• Supply voltage range from 4.5V to 5.25V
• Supply current of 120mA at VCC = 5V, EN = high
• Maximum shutdown current of 230µA at VCC = 5V, EN = low
• Baseband frequency range from DC to 460MHz
• LO input return loss of 15dB (Z0 = 50 ohm, PLO = 0dBm)
• RF output return loss of 13.5dB (Z0 = 50 ohm)
• Conversion gain of -2.5dB (PRF = -10dBm, PLO = 0dBm, defined as PRF/P)

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