Quadrature demodulator

A monolithic IF quadrature demodulator from Linear Technology operates with a single supply voltage down to 1.8.

The LT5546 has applications in GPS receivers, wireless local loop, satellite IF receivers and mobile wireless data receivers. The device accepts an IF input signal from 40 to 500 MHz.

It incorporates a precision quadrature phase-shifter for accurate I/Q demodulation and a low distortion variable gain amplifier with a log-linear gain control range from -7 to 56 dB.

The demodulated I/Q baseband signals pass through on-chip 17 MHz low-pass noise reduction filters, reducing the need for external filtering. The I/Q outputs are buffered by low distortion, high linearity amplifiers.

When signals are momentarily too high due to excessive VGA gain, the device's output amplifiers limit symmetrically, ensuring rapid recovery from signal overload after the VGA gain is adjusted. Moreover, the LT5546 includes an on-chip signal power detector with a detection range of -30 to +8 dBm to assist in high signal level detection and corresponding gain adjustment.