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
p e r m a n e n t l y a c t i v e . T h i s f e a t u r e i s
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.

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.

FET BIAS CONTROLLER AND
POLARITY SWITCH

ISSUE 1 - FEBRUARY 1998

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

APPLICATIONS

Satellite receiver LNBs

Private mobile radio (PMR)

Cellular telephones

ZNBG3010
ZNBG3011

4-114

ABSOLUTE MAXIMUM RATINGS

Supply Voltage

-0.6V to 12V

Supply Current

100mA

Input Voltage (V

POL

)

25V Continuous

Drain Current (per FET)

0 to 15mA

(set by R

CAL

)

Operating Temperature

-40 to 70°C

Storage Temperature

-50 to 85°C

Power Dissipation (T

amb

25°C)

QSOP16

500mW

ELECTRICAL CHARACTERISTICS TEST CONDITIONS
(Unless otherwise stated):T

amb

25°C,V

=5V,I

=10mA (R

CAL

=33k

)

SYMBOL PARAMETER

CONDITIONS

LIMITS

UNITS

MIN.

TYP.

MAX.

Supply Voltage

Supply Current

to I

and I

=10mA, V

POL

=14V

and

=10mA, V

POL

=15.5V

10
30
30

mA
mA
mA

SUB

Substrate Voltage
(Internally generated)

SUB

=-200

-3.5

-3.0

-2
-2

V
V

Output Noise
Drain Voltage
Gate Voltage

=4.7nF, C

=10nF

=4.7nF, C

=10nF

0.02
0.005

Vpkpk
Vpkpk

Oscillator Frequency

200

350

800

kHz

GATE CHARACTERISTICS

Output Current Range

-30

2000

POL

GOx

(mA)

(V)

(

µ
µ

G1O

G1L

G1H

Output Voltage
Gate 1 Off
Low
High

POL

=14

GO1

=-10

=12 V

POL

=15.5 I

GO1

=-10

POL

=15.5 I

GO1

-3.5
-3.5
0.4

-2.9
-2.9
0.75

-2.0
-2.0
1.0

V
V
V

G2O

G2L

G2H

Output Voltage
Gate 2 Off
Low
High

POL

=15.5 I

GO2

=-10

=12 V

POL

=14

GO2

=-10

POL

=14

GO2

-3.5
-3.5
0.4

-2.9
-2.9
0.75

-2.0
-2.0
1.0

V
V
V

G3L

G3H

Output Voltage
Gate 3 Low
High

=12

GO3

=-10

GO3

-3.5
0.4

-2.9
0.75

-2.0
1.0

V
V

ZNBG3010
ZNBG3011

4-115

SYMBOL PARAMETER

CONDITIONS

LIMITS

UNITS

MIN.

TYP.

MAX.

DRAIN CHARACTERISTICS

Current

Current Change
with V

with T

= 5 to 10V

=-40 to +70°C

0.2
0.05

%/V
%/°C

Drain 1 Voltage:High
ZNBG3010
ZNBG3011

=10mA, V

POL

=15.5V

=10mA, V

POL

=15.5V

2.0
1.8

2.2
2.0

2.4
2.2

V
V

Drain 2 Voltage:High
ZNBG3010
ZNBG3011

=10mA, V

POL

=14V

=10mA, V

POL

=14V

2.0
1.8

2.2
2.0

2.4
2.2

V
V

Drain 3 Voltage:High
ZNBG3010
ZNBG3011

=10mA,

POL

=15.5V

=10mA, V

POL

=15.5V

2.0
1.8

2.2
2.0

2.4
2.2

V
V

Voltage Change
with V

with T

= 5 to 10V

=-40 to +70°C

0.5
50

%/V
ppm

Leakage Current
Drain 1
Drain 2

=0.1V, V

POL

=14V

=0.1V, V

POL

=15.5V

10
10

POLARITY SWITCH CHARACTERISTICS

POL

Input Current

POL

=25V

(Applied via R

POL

=10k

TPOL

Threshold Voltage

(Applied via R

POL

=10k

14.75

15.5

SPOL

Switching Speed

100

Notes:

1. The negative bias voltages specified are generated on-chip using an internal oscillator. Two external
capacitors, C

and C

SUB

, of 47nF are required for this purpose.

2. The characteristics are measured using an external reference resistor R

CAL

of value 33k wired from

pins R

CAL

to ground.

3. Noise voltage is not measured in production.

4. Noise voltage measurement is made with FETs and gate and drain capacitors in place on all
outputs. C

, 4.7nF, are connected between gate outputs and ground, C

, 10nF, are connected

between drain outputs and ground.

ZNBG3010
ZNBG3011

4-116

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 ZNBG3010/11 contains 3 such stages. The
negative rail generator is common to both devices.

The drain voltage of the external FET Q

is set by the ZNBG device to its normal operating voltage.

This is determined by the on board V

Set reference, for the ZNBG3010 this is nominally 2.2 volts

whilst the ZNBG3011 provides nominally 2 volts.

The drain current taken by the FET is monitored by the low value resistor I

Sense. The amplifier

driving the gate of the FET adjusts the gate voltage of Q

so that the drain current taken matches

the current called for by an external resistor R

CAL

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, C

and C

SUB

ZNBG3010
ZNBG3011

4-118

APPLICATIONS 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 C

and C

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 C

and C

SUB

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 C

and C

SUB

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 C

SUB

pin.

Resistor R

CAL

sets the drain current at which all external FETs are operated. 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.

The ZNBG devices have been designed to protect the external FETs from adverse operating
conditions. With a JFET connected to any bias circuit, the gate output voltage of the bias circuit
can not exceed the range -3.5V to 1V, under any conditions including powerup and powerdown
transients. Should the negative bias generator be shorted or overloaded so that the drain current
of the external FETs can no longer be controlled, the drain supply to FETs is shut down to avoid
damage to the FETs by excessive drain current.

ZNBG3010
ZNBG3011

4-120

The following schematic shows the function of the V

POL

input. Only one of the two external FETs

numberd Q1 and Q2 are powered at any one time, their selection is controlled by the input V

POL

This input is designed to be wired to the power input of the LNB via a high value (10k) resistor.
With the input voltage of the LNB set at or below 14V, FET Q2 will be enabled. With the input
voltage at or above 15.5V, FET Q1 will be enabled. The disabled FET has its gate driven low and
its drain terminal is switched open circuit. It is permissible to connect the drain pins D1 and D2
together if required by the application circuit. FET number Q3 is always active regardless of the
voltage applied to V

POL

Control Input Switch Function

Input Sense

Polarisation

Select

14 volts

Vertical

FET Q2

15.5 volts

Horizontal

FET Q1

ZNBG3010
ZNBG3011

4-119

Single Standard/ Enhanced LNB block diagram.

The following block diagram shows the main section of an LNB designed for use with the Astra
series of satellites. The ZNBG3010/11 is the core bias and control element of this circuit. The
ZNBG provides the negative rail, FET bias control and polarisation switch control, with the
minimum of external components. Compared to other discrete component solutions the ZNBG
circuit reduces component count and overall size required.

APPLICATIONS INFORMATION (Continued)

ZNBG3010
ZNBG3011

4-121

PACKAGE DIMENSIONS

PIN No.1

IDENTIFICATION
RECESS
FOR PIN 1

Millimetres

Inches

MIN

MAX

MIN

MAX

4.80

4.90

0.189

0.196

0.635

0.025 NOM

0.177

0.267

0.007

0.011

0.20

0.30

0.008

0.012

3.81

3.99

0.15

0.157

1.35

1.75

0.053

0.069

0.10

0.25

0.004

0.01

5.79

6.20

0.228

0.244

0°

8°

0°

8°

Zetex plc.
Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom.
Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries)
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Zetex plc 1998

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This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be
used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating
to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price
or conditions of supply of any product or service.

ZNBG3010
ZNBG3011

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