ZNBG3116

FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION ISSUE 1 - JUNE 2001 DEVICE DESCRIPTION The ZNBG series of devices are designed to meet the bias requirements of GaAs and HEMT FETs commonly used in satellite receiver LNBs, PMR, cellular telephones etc. with a minimum of external components. With the addition of two capacitors and a resistor the devices provide drain voltage and current control for three external grounded source FETs, generating the regulated negative rail required for FET gate biasing whilst operating from a single supply. This negative bias, at -2.8 volts, can also be used to supply other external circuits. The ZNBG3115/16 includes bias circuits to drive up to three external FETs. A control input to the device selects either one of two FETs as operational, the third FET is permanently active. This feature is normally used as an LNB polarisation switch. Also specific to Universal LNB applications is the 22kHz tone detection and logic output feature which is used to enable high and low band frequency switching. The ZNBG3115/16 has been designed to cope with DiSEqC™ ready set top boxes and rejects all transients from channel switching. ZNBG3115 ZNBG3116 Drain current setting of the ZNBG3115/16 is user selectable over the range 0 to 15mA, this is achieved with addition of a single resistor. The series also offers the choice of drain voltage to be set for the FETs, the 3115 gives 2.2 volts drain whilst the 3116 gives 2 volts. These devices are unc...