ANALOG DEVICES DC678A

Demonstration circuit 678A is a 40MHz to 900MHz direct conversion quadrature demodulator featuring the LT5517. The LT5517 is a direct conversion quadrature demodulator optimized for high linearity receiver applications where high dynamic range is important. It is suitable for communications receivers where an RF signal is directly converted into I and Q baseband signals with a bandwidth up to 130MHz. LT5517 incorporates balanced I and Q mixers, LO buffer amplifiers and a precision, broadband quadrature generator derived from an on-chip divide-by-two circuit. Superior linearity and low noise performance of LT5517 is achieved across its full frequency range. A well-balanced divide-by-two circuit generates precision quadrature LO carriers to drive I mixer and Q mixer. Consequently, the outputs of I-ch and Q-ch are well matched in amplitude, and their phases are 90˚ apart. LT5517 also provides excellent 50 ohm impedance matching at the 2XLO port across its entire frequency range.