40MHz to 500MHz Quadrature Demodulator with VGA

The LT5506 is a 40MHz to 500MHz monolithic integrated quadrature demodulator with variable gain amplifier (VGA), designed for low voltage operation. It supports standards that use a linear modulation format. The chip consists of a VGA, quadrature down-converting mixers and lowpass noise filters. The LO port consists of a divide-by-two stage and LO buffers. The IC provides all building blocks for IF down-conversion to I and Q baseband signals with a single supply voltage of 1.8V to 5.25V. The VGA gain has a linear-in- dB relationship to the control input voltage. Hard-clipping amplifiers at the mixer outputs reduce the recovery time from a signal overload condition. The lowpass filters reduce the out-of-band noise and spurious frequency components. The cut-off frequency of the noise filters is approximately 8.8MHz. The external 2xLO frequency is required to be twice the IF input frequency for the mixers. The standby mode provides reduced supply current and fast transient response into the normal operating mode when the I/Q outputs are AC-coupled to a baseband chip.

Applications

* IEEE802.11

* High Speed Wireless LAN

* Wireless Local Loop

* Wide Range 1.8V to 5.25V Supply

* Frequency Range: 40MHz to 500MHz

* –4dB to 59dB Variable Power Gain

* THD < 0.12% (–58dBc) at 800mVP-P Differential Output Level

* 8.8MHz I/Q Lowpass Output Noise Filters

* IF Overload Detector

* Baseband I/Q Amplitude Imbalance: 0.2dB

* Baseband I/Q Phase Imbalance: 0.6°

* 6.8dB Noise Figure at Max Gain

* Input IP3 at Low Gain: –0.5dBm

* Low Supply Current: 27mA

* Low Delay Shift Over Gain Control Range: 2ps/dB

* Outputs Biased Up While in Standby

* 16-Lead QFN 4mm x 4mm Package with Exposed Pad