ZNBR4000

The ZNBR 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 and a VCC of 3-6V for improved efficiency. With the addition of two capacitors and resistors the ZNBG4000/1 and ZNBG6000/1 devices provide drain voltage and current control for a number of 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 ZNBR4000/1 and ZNBR6000/1 contain four and six bias stages respectively. In setting drain current the ZNBR4000/1 two resistors allows individual FET pair control to different levels, the ZNBR6000/1 two resistors split control between two and four FETs. This allows the operating current of input FETs to be adjusted to minimise noise, whilst the following FET stages can separately be adjusted for maximum gain. The series also offers the choice of drain voltage to be set for the FETs, the ZNBR4000/6000 gives 2.2 volts drain whilst the ZNBR4001/6001 gives 2 volts.

These ZNBG4000/1 and ZNBG6000/1 devices are unconditionally stable over the full working temperature with the FETs in place, subject to the inclusion of the recommended gate and drain capacitors. These ensure RF stability and minimal injected noise.

ZNBG4000/1 and ZNBG6000/1 are   possible to use less than the devices full complement of FET bias controls, unused   drain and gate connections can be left open circuit without affecting operation of the remaining bias circuits.

In order to protect the external FETs the ZNBG4000/1 and ZNBG6000/1 circuits have been designed to ensure that, under any conditions including power  up/down transients, the gate drive from the bias circuits cannot exceed the range -2.5V to 0.7V. Furthermore if the negative rail  experiences a fault condition, such as overload or short circuit, the drain supply to the FETs will shut down avoiding excessive current flow.

The ZNBR4000/1 and ZNBR6000/1 are available in QSOP16 and 20 pin packages  respectively for the minimum in devices size. Device operating temperature is -40 to 70°C to suit a wide range of environmental conditions.