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ZNBG6000 Schematic ( PDF Datasheet ) - Zetex Semiconductors

Teilenummer ZNBG6000
Beschreibung FET BIAS CONTROLLER
Hersteller Zetex Semiconductors
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Gesamt 10 Seiten
ZNBG6000 Datasheet, Funktion
FET BIAS CONTROLLER
ISSUE 2 - JUNE 1998
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
resistors the 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 ZNBG4000/1 and ZNBG6000/1 contain
four and six bias stages respectively. In
setting drain current the ZNBG4000/1 two
resistors allows individual FET pair control
to different levels, the ZNBG6000/1 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
ZNBG4000/6000 gives 2.2 volts drain whilst
the ZNBG4001/6001 gives 2 volts.
FEATURES
Provides bias for GaAs and HEMT FETs
Drives up to four or six FETs
Dynamic FET protection
Drain current set by external resistor
Regulated negative rail generator
requires only 2 external capacitors
Choice in drain voltage
Wide supply voltage range
QSOP surface mount package
ZNBG4000 ZNBG4001
ZNBG6000 ZNBG6001
These 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.
It is 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
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 -3.5V
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 ZNBG4000/1 and ZNBG6000/1 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.
APPLICATIONS
Satellite receiver LNBs
Private mobile radio (PMR)
Cellular telephones
4-137






ZNBG6000 Datasheet, Funktion
ZNBG4000 ZNBG4001
ZNBG6000 ZNBG6001
TYPICAL APPLICATION CIRCUIT
APPLICATIONS INFORMATION
The above is a partial application circuit for the ZNBG series showing all external components
required for appropriate biasing. The bias circuits are unconditionally stable over the full
temperature range with the associated FETs and gate and drain capacitors in circuit.
Capacitors CD and CG ensure that residual power supply and substrate generator noise is not
allowed to affect other external circuits which may be sensitive to RF interference. They also
serve to suppress any potential RF feedthrough between stages via the ZNBG device. These
capacitors are required for all stages used. Values of 10nF and 4.7nF respectively are
recommended however this is design dependent and any value between 1nF and 100nF could
be used.
The capacitors CNB and CSUB are an integral part of the ZNBGs negative supply generator. The
negative bias voltage is generated on-chip using an internal oscillator. The required value of
capacitors CNB and CSUB is 47nF. This generator produces a low current supply of approximately
-3 volts. Although this generator is intended purely to bias the external FETs, it can be used to
power other external circuits via the CSUB pin.
Resistors RCAL1/2 sets the drain current at which all external FETs are operated. Both ZNBG devices
have the facility to program different drain currents into selected FETs. Two RCAL inputs are
provided. For the ZNBG4000, resistor RCAL1 sets the drain current of FETs 1 and 2, resistor RCAL2
sets the drain current of FETs 3 and 4. For the ZNBG6000, resistor RCAL1 sets the drain current
of FETs 1 and 4, resistor RCAL2 sets the drain current of FETs 2, 3, 5 and 6. If the same drain current
is required for all FETs on either device then pins RCAL1 and RCAL2 can be wired together and
shunted to ground by a single calibration resistor of half normal value.
If any bias control circuit is not required, its related drain and gate connections may be left open
circuit without affecting the operation of the remaining bias circuits. If all FETs associated with
a current setting resistor are omitted, the particular RCAL should still be included. The supply
current can be reduced, if required, by using a high value RCAL resistor (e.g. 470k).
4-142

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