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ZNBG3211 Schematic ( PDF Datasheet ) - Zetex Semiconductors

Teilenummer ZNBG3211
Beschreibung FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION
Hersteller Zetex Semiconductors
Logo Zetex Semiconductors Logo 




Gesamt 16 Seiten
ZNBG3211 Datasheet, Funktion
FET BIAS CONTROLLER WITH POLARISATION ZNBG3210
SWITCH AND TONE DETECTION
ZNBG3211
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 DiSEqCtone 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
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 -
supporting zero volt gate switching
topology.
22kHz tone detection for band switching
Compliant with ASTRA control
specifications
QSOP surface mount package
is achieved with the addition of a single
resistor. The series also offers the choice of
FET drain voltage, the 3210 gives 2.2 volts
drain whilst the 3211 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 ZNBG3210/11 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.
APPLICATIONS
Satellite receiver LNBs
Private mobile radio (PMR)
Cellular telephones
67-1






ZNBG3211 Datasheet, Funktion
ZNBG3210
ZNBG3211
TYPICAL CHARACTERISTICS
16
Vcc = 5V
14
12
10
8
6
4
2
0
0
20 40 60 80
Rcal (k)
JFET Drain Current v Rcal
100
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
0
Note:- Operation with loads > 200µA
is not guaranteed.
Vcc = 5V
6V
8V
10V
0.2 0.4 0.6 0.8
External Vsub Load (mA)
Vsub v External Load
1.0
2.4
ZNBG3210 ONLY
2.3
2.2
Vcc = 5V
6V
8V
2.1 10V
2.0
2 4 6 8 10 12 14 16
Drain Current (mA)
JFET Drain Voltage v Drain Current
2.2
ZNBG3211 ONLY
2.1
2.0
Vcc = 5V
6V
8V
1.9 10V
1.8
2 4 6 8 10 12 14 16
Drain Current (mA)
JFET Drain Voltage v Drain Current
67-6

6 Page









ZNBG3211 pdf, datenblatt
ZNBG3210
ZNBG3211
The following block diagram shows the main section of an LNB designed for use with the Astra
series of satellites. The ZNBG3210/11 is the core bias and control element of this circuit. The
ZNBG provides the negative rail, FET bias control, polarisation switch control, tone detection and
band switching with the minimum of external components. Compared to other discrete
component solutions the ZNBG circuit reduces component count and overall size required.
Single Universal LNB Block Diagram
Tone detection and band switching is provided on the ZNBG3210/11 devices. The following
diagrams describes how this feature operates in an LNB and the external components required.
The presence or absence of a 22kHz tone applied to pin FIN enables one of two outputs, LB and
HB. A tone present enables HB and tone absent enables LB. The LB and HB outputs are designed
to be compatible with both MMIC and discrete local oscillator applications, selected by pin LOV.
Referring to Figure 1 wiring pin LOV to ground will force LB and HB to switch between -2.6V
(disabled) and 0V (enabled). Referring to Figure 2 wiring pin LOV to a positive voltage source (e.g.
a potential divider across VCC and ground set to the required oscillator supply voltage, VOSC) will
force the LB and HB outputs to provide the required oscillator supply, VOSC, when enabled.
Tone Detection Function
LOV
FIN
LB
HB LB
HB
GND
22kHz
Disabled
Enabled
-2.6 volts
GND
Enabled
Disabled
GND
-2.6 volts
VOSC
22kHz
Disabled
Enabled
Note 1
VOSC
Enabled
Disabled
VOSC
Note 1
Note 1: 0 volts in typical LNB applications but dependent on extenal circuits.
67-12

12 Page





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