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.

• Designed for operations in the frequency range between 40MHz and 900MHz
• Supply voltage range from 4.5V to 5.25V
• Supply current of 90mA (VCC = 5V, EN = high)
• Maximum shutdown current of 20µA (VCC = 5V, EN = low)
• 2XLO frequency range from 80MHz to 1800MHz
• 2XLO input power range from -15dBm to 0dBm
• Conversion gain of 3.3dB (voltage gain, load impedance = 1Kohm, PRF = -10dBm, P2XLO = -10dBm)
• Noise figure of 12.4dB (P2XLO= -10dBm)
• Baseband bandwidth of 130MHz

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