A wide dynamic range GaAs broadcast satellite tuner IC

Abstract

Broadcast satellite tuners (BS tuners) used in set top boxes are fed a 950-2150 MHz input from the satellite dish IF. In apartment complexes the IF signal can be split, amplified, and supplied to many units. This IF input spectrum can consist of as many as 50 channels, each ranging in levels from -75 dBm to -15 dBm. Consequently the linearity requirements of the BS tuner are stringent. Typically pin diode attenuators are used at the input of the BS tuner to absorb this dynamic range. A transistor, the bootstrapped gate FET (BGFET), is small and behaves as a low-distortion variable resistor. Using this linear transistor, a BS tuner IC has an IIP3>+10 dBm and an AGC range of 20 dB. The noise figure over the full RF band of 950-2150 MHz is less than 7 dB. The circuit contains an LNA, AG, mixer, and oscillator and draws 50 mA from a +5 V supply. The chip is 0.37 mm/sup 2/ in a low-power GaAs MESFET technology and is packaged in an SOIC-16 package. The circuit is 4 times smaller than a previous GaAs BS tuner.