40MHz to 500MHz VGA and I/Q Demodulator with 17MHz Baseband Bandwidth

The LT5546 is a 40MHz to 500MHz monolithic integrated quadrature demodulator with variable gain amplifier (VGA) and 17MHz I/Q baseband bandwidth 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 17MHz lowpass noise filters (LPF). 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 –3dB corner frequency of the noise filters is approximately 17MHz and has a first order roll-off. 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

* GPS IF Receivers

* Satellite IF Receivers

* VHF/UHF Receivers

* Wireless Local Loop

* 17MHz I/Q Lowpass Output Noise Filters

* Wide Range 1.8V to 5.25V Supply Voltage

* Frequency Range: 40MHz to 500MHz

* THD < 0.14% (–57dBc) at 800mVP-P Differential Output Level

* IF Overload Detector

* Log Linear Gain Control Range: –7dB to 56dB

* Baseband I/Q Amplitude Imbalance: 0.2dB

* Baseband I/Q Phase Imbalance: 0.6°

* 7.8dB Noise Figure at Max Gain

* Input IP3 at Low Gain: –1dBm

* Low Supply Current: 24mA

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

* Outputs Biased Up While in Standby

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