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Linear Tech demodulator's SFDR surpasses 80dB

Posted: 19 Oct 2004 ?? ?Print Version ?Bookmark and Share

Keywords:linear technology? i/q demodulator? lt5517?

Linear Technology Corp. announced that its new very high linearity and low noise I/Q demodulator provides the performance needed for direct conversion and IF conversion of radio signals to baseband for high performance receivers.

The LT5517 has an IIP3 (Input Third-Order Intercept Point) of 23.5dBm and a Noise Figure of 9.5dB at 200MHz, allowing the robust detection of weak signals, even in the presence of high level interference. This performance results in a Spurious Free Dynamic Range (SFDR) exceeding 80dB.

With a precision 0 and 90 phase splitter, the new device provides accurate I (In phase) and Q (Quadrature phase) demodulation of RF signals, ranging from 40MHz to 900MHz, directly to baseband in a compact solution. In addition, the demodulator offers a high level of integration, incorporating a pair of matched high linearity mixers, with an on-chip quadrature phase generator and splitter. The I and Q signal paths are internally gain matched to 0.03dB typical, with a typical phase mismatch of 0.7, resulting in highly accurate I and Q demodulation. The differential I and Q outputs have low DC offset, typically 0.5mV, and built-in 130MHz low-pass filters to remove out-of-band noise.

The internal quadrature phase splitter uses a Local Oscillator (LO) derived from a divide-by-two circuit. Correspondingly, the 2XLO input port accepts a signal at twice the LO frequency, thus minimizing LO leakage to the RF port. Additionally, the company said, the LT5517 has excellent port-to-port RF leakage, reducing external RF filtering requirements. The 2XLO input requires only a -5dBm drive level, and is internally matched to 50 ohms.

Designed for IF and RF demodulators in high performance, wireless infrastructure receiver applications, the LT5517 operates from a single 4.5V to 5.25V supply, drawing a power supply current of 90mA. An Enable pin allows the device to power down, drawing a typical OFF-state current of 0.1?A. Turn-on and turn-off time is typically under 300ns.

Housed in a 16-lead 4-by-4mm surface mount QFN package, the LT5517 is priced at $7.40 each in 1,000-piece quantities.

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