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Zetex Semiconductors |
FET BIAS CONTROLLER AND
POLARITY SWITCH
ISSUE 1 - FEBRUARY 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 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 ZNBG3010/11 includes bias circuits to
drive up to three external FETs. A control
input to the device selects either one of two
FETs as operational, the third FET is
permanently active. This feature is
particularly used as an LNB polarisation
switch.
Drain current setting of the ZNBG3010/11 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
ZNBG3010 gives 2.2 volts drain whilst the
ZNBG3011 gives 2 volts.
FEATURES
• Provides bias for GaAs and HEMT FETs
• Drives up to three 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
• Polarisation switch for LNBs
• QSOP surface mount package
ZNBG3010
ZNBG3011
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 1V. 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 ZNBG3010/11 are available in QSOP16
for the minimum in device 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
4-114
ZNBG3010
ZNBG3011
ABSOLUTE MAXIMUM RATINGS
Supply Voltage
-0.6V to 12V
Supply Current
100mA
Input Voltage (VPOL)
Drain Current (per FET)
(set by RCAL)
Operating Temperature
25V Continuous
0 to 15mA
-40 to 70°C
Storage Temperature
-50 to 85°C
Power Dissipation (Tamb= 25°C)
QSOP16
500mW
ELECTRICAL CHARACTERISTICS TEST CONDITIONS
(Unless otherwise stated):Tamb= 25°C,VCC=5V,ID=10mA (RCAL=33kΩ)
SYMBOL PARAMETER
CONDITIONS
LIMITS
UNITS
MIN. TYP. MAX.
VCC Supply Voltage
5 10 V
ICC
Supply Current
ID1 to ID3=0
ID2 and ID3=10mA, VPOL=14V
ID1 and ID3=10mA, VPOL=15.5V
10 mA
30 mA
30 mA
VSUB
Substrate Voltage ISUB=0
(Internally generated) ISUB=-200µA
-3.5 -3.0 -2
-2
V
V
Output Noise
END Drain Voltage
ENG Gate Voltage
CG=4.7nF, CD=10nF
CG=4.7nF, CD=10nF
0.02 Vpkpk
0.005 Vpkpk
fO Oscillator Frequency
GATE CHARACTERISTICS
200 350 800 kHz
IGO
VG1O
VG1L
VG1H
VG2O
VG2L
VG2H
VG3L
VG3H
Output Current Range
-30
IDx VPOL
(mA) (V)
IGOx
(µA)
Output Voltage
Gate 1 Off
Low
High
ID1=0 VPOL=14 IGO1=-10
ID1=12 VPOL=15.5 IGO1=-10
ID1=8 VPOL=15.5 IGO1=0
-3.5
-3.5
0.4
Output Voltage
Gate 2 Off
Low
High
ID2=0 VPOL=15.5 IGO2=-10
ID2=12 VPOL=14 IGO2=-10
ID2=8 VPOL=14 IGO2=0
-3.5
-3.5
0.4
Output Voltage
Gate 3 Low
High
ID3=12
ID3=8
IGO3=-10 -3.5
IGO3=0 0.4
-2.9
-2.9
0.75
-2.9
-2.9
0.75
-2.9
0.75
2000 µA
-2.0 V
-2.0 V
1.0 V
-2.0 V
-2.0 V
1.0 V
-2.0 V
1.0 V
4-115
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