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零件编号 | ZNBG3111 | ||
描述 | FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION | ||
制造商 | Zetex Semiconductors | ||
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FET BIAS CONTROLLER WITH POLARISATION ZNBG3110
SWITCH AND TONE DETECTION
ZNBG3111
ISSUE 2 - APRIL 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 ZNBG3110/11 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. Also specific to LNB applications is
the 22KHz tone detection and logic output
feature which is used to enable high and low
band frequency switching.
Drain current setting of the ZNBG3110/11 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 3110 gives
2.2 volts drain whilst the 3111 gives 2 volts.
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 ZNBG3110/11 are available in QSOP20
for the minimum in device size. Device
operating temperature is -40 to 70°C to suit
a wide range of environmental conditions.
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
• 22KHz tone detection for band
switching
• Compliant with ASTRA control
specifications
• QSOP surface mount package
APPLICATIONS
• Satellite receiver LNBs
• Private mobile radio (PMR)
• Cellular telephones
4-123
ZNBG3110
ZNBG3111
FUNCTIONAL DIAGRAM
FUNCTIONAL DESCRIPTION
The ZNBG devices provide all the bias requirements for external FETs, including the generation
of the negative supply required for gate biasing, from the single supply voltage.The diagram
above shows a single stage from the ZNBG series. The ZNBG3110/11 contains 3 such stages. The
negative rail generator is common to both devices.
The drain voltage of the external FET QN is set by the ZNBG device to its normal operating voltage.
This is determined by the on board VD Set reference, for the ZNBG3110 this is nominally 2.2 volts
whilst the ZNBG3111 provides nominally 2 volts.
The drain current taken by the FET is monitored by the low value resistor ID Sense. The amplifier
driving the gate of the FET adjusts the gate voltage of QN so that the drain current taken matches
the current called for by an external resistor RCAL.
Since the FET is a depletion mode transistor, it is often necessary to drive its gate negative with
respect to ground to obtain the required drain current. To provide this capability powered from
a single positive supply, the device includes a low current negative supply generator. This
generator uses an internal oscillator and two external capacitors, CNB and CSUB.
4-130
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ZNBG3110
ZNBG3111
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页数 | 16 页 | ||
下载 | [ ZNBG3111.PDF 数据手册 ] |
零件编号 | 描述 | 制造商 |
ZNBG3110 | FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION | Zetex Semiconductors |
ZNBG3111 | FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION | Zetex Semiconductors |
ZNBG3113 | FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION | Zetex Semiconductors |
ZNBG3114 | FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION | Zetex Semiconductors |
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