New 40 - 900 MHz Quadrature Demodulator Offers High Spurious-Free Dynamic Range

Milpitas, CA -- A new, very high linearity and low noise I/Q demodulator from Linear Technology Corporation 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 23.5 dBm and a Noise Figure of 9.5 dB at 200 MHz, 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 80 dB. The LT5517 integrates a precision 0° and 90° phase splitter, providing accurate I (In phase) and Q (Quadrature phase) demodulation of RF signals, ranging from 40 to 900 MHz, directly to baseband in a compact solution.

The LT5517 is well suited for IF and RF demodulators in high performance, wireless infrastructure receiver applications. Other applications include micro-basestations, repeater cells, RFID readers, and broadband fixed wireless access.

The LT5517 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 0.03 dB typical, with a typical phase mismatch of 0.7 degree, resulting in highly accurate I and Q demodulation. The differential I and Q outputs have low DC offset, typically 0.5 mV, and built-in 130 MHz low-pass filters to remove out-of-band noise. The LT5517 provides a compact and robust receiver solution.

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. Moreover, the LT5517 has excellent port-to-port RF leakage, reducing external RF filtering requirements. The 2XLO input requires only a -5 dBm drive level, and is internally matched to 50 Ohms, thus providing a simple, single-ended interface.

LT5517 operates from a single 4.5 to 5.25 V supply, drawing a power supply current of 90 mA. An Enable pin allows the device to power down, drawing a typical OFF-state current of 0.1 uA. Turn-on and turn-off time is typically under 300 ns. The device is offered in a 16-lead 4 x 4 mm surface-mount QFN package.

Source: Linear Technology