ZNBG3210Q20

FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION ISSUE 2 - FEBRUARY 2000 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 -3 volts, can also be used to supply other external circuits. The ZNBG3210/11 includes bias circuits to drive up to three external FETs. A control input to the device selects either one of two FETs as operational using 0V gate switching methodology, the third FET is permanently active. This feature is particularly used as an LNB polarisation switch. Also specific to LNB applications is the enhanced 22kHz tone detection and logic output feature which is used to enable high and low band frequency switching. The detector has been specifically designed to reject inerference such as low frequency signals and DiSEqC tone bursts - without the use of additional external components. Drain current setting of the ZNBG3210/11 is user selectable over the range 0 to 15mA, this ZNBG3210 ZNBG3211 is achieved with the addition of a single resistor. The series also offers the choice of FET drain voltage, the 3210 gi...