FET BIAS CONTROLLER WITH POLARISATION
SWITCH AND TONE DETECTION

ISSUE 1 - OCTOBER 1998

ZNBG3113
ZNBG3114

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 ZNBG3113/14 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. 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.

The facility to control the tone switching
delay is provided. This allows the rejection
of other lower frequency tones tat may be
present in multiple LNB applications.

Drain current setting of the ZNBG3113/14 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 3113 gives
2.2 volts drain whilst the 3114 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.

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 ZNBG3113/14 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

Programmable tone delay

Compliant with ASTRA control
specifications

QSOP surface mount package

APPLICATIONS

Satellite receiver LNBs

Private mobile radio (PMR)

Cellular telephones

4-123

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)

QSOP20

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

=0,I

to I

=10mA, V

POL

=14V

=0,I

to I

=10mA, V

POL

=15.5V

=0, I

=10mA

=0, I

=10mA

15
35
35
45
45

mA
mA
mA
mA
mA

SUB

Substrate Voltage (Internally generated) I

SUB

=-200

-3.5

-3.0

-2.5
-2.4

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

ZNBG3113
ZNBG3114

4-124

SYMBOL PARAMETER

CONDITIONS

LIMITS

UNITS

MIN.

TYP.

MAX.

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

-2.7
-2.7
0.4

-2.4
-2.4
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

-2.7
-2.7
0.4

-2.4
-2.4
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

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
ZNBG3113
ZNBG3114

=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
ZNBG3113
ZNBG3114

=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
ZNBG3113
ZNBG3114

=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

ZNBG3113
ZNBG3114

4-125

SYMBOL PARAMETER

CONDITIONS

LIMITS

UNITS

MIN.

TYP.

MAX.

TONE DETECTION CHARACTERISTICS

Filter Amplifier
Input Bias Current

=150k

0.04

0.15

1.0

OUT

Output Voltage

=150k

1.75

1.95

2.05

OUT

Output Current

OUT

=1.96V, V

FIN

=2.1V

400

520

650

Voltage Gain

f=22kHz,V

=1mV

OUT

Rectifier
Output Voltage

=150k

=-10

1.8

2.0

2.2

LEAK

Leakage Current

=150k

OUT

=3V

200

Comparator
Threshold
Voltage

f=0

2.95

3.2

3.45

LOV

Output Stage
L

Volt. Range

=50mA(L

or H

)

-0.5

-1.8 V

LOV

Bias Current

LOV

0.04

0.15

1.0

LBL

Output Low

LOV

=-10

Enabled

LOV

=3V I

Enabled

-3.5
-0.01

-2.75
0

-2.5
0.01

V
V

LBH

Output High

LOV

=10mA

Disabled

LOV

=3V I

=50mA

Disabled

-0.025
2.9

0
3.0

0.025
3.1

V
V

HBL

Output Low

LOV

=-10

Enabled

LOV

=3V I

Enabled

-3.5
-0.01

-2.75
0

-2.5
0.01

V
V

HBH

Output High

LOV

=10mA

Disabled

LOV

=3V I

=50mA

Disabled

-0.025
2.9

0
3.0

0.025
3.1

V
V

POLARITY SWITCH CHARACTERISTICS

POL

Input Current

POL

=25V (Applied via R

POL

=10k

)

TPOL

Threshold
Voltage

POL

=25V (Applied via R

POL

=10k

)

14.75

15.5

SPOL

Switching Speed

POL

=25V (Applied via R

POL

=10k

)

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.

5 . These parameters are lneearly related to V

6. These parameters are measured using Test Circuit 1
7. These parameters are measured using Test Circuit 2

ZNBG3113
ZNBG3114

4-126

Filter Response

100

10k

100k

0.2

0.4

0.6

0.8

1.0

Frequency (Hz)

1.2

1.4

Stability Boundary

10nF

100nF

1.0

LB/HB Load Capacitance

1uF

0.1

100

1nF

100pF

10pF

Stable region

Open Loop Phase v Frequency

100

10k

100k

120

Frequency (Hz)

150

180

10M

LB/HB Dropout Voltage v Load Current

1.3

1.4

1.5

1.6

1.7

Load Current (mA)

1.8

1.9

1.2

2.0

LB/HB Offset Voltage v Load Current

-8

-6

-4

-2

Load Current (mA)

Open Loop Gain v Frequency

100

10k

100k

Frequency (Hz)

10M

= 5V

=0.1Vpkpk

Test Circuit 1

= 5V

Tamb = -40 C

amb

= 25°C

amb

= 70°C

= 5V

amb

= -40°C

amb

= 25°C

amb

= 70°C

LOV

= 0V

Vcc = 5V

TYPICAL CHARACTERISTICS

Unstable Region

ZNBG3113
ZNBG3114

4-129

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 ZNBG3113/14 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 ZNBG3113 this is nominally 2.2 volts

whilst the ZNBG3114 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 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

4-130

ZNBG3113
ZNBG3114

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

4-131

ZNBG3113
ZNBG3114

For many LNB applications tone detection and band switching is required. The ZNBG3113/14
includes the circuitry necessary to detect the presence of a 22kHz tone modulated on the supply
input to the LNB. Referring to the following schematic diagram, the main elements of this detector
are an op-amp enabling the construction of a Sallen Key filter, a rectifier/smoother and a
comparator. Full control is given over the centre frequency and bandwidth of the filter by the
selection of two external resistors and capacitors (one of these resistors, R2, shares the function
of overvoltage protection of pin V

POL

Pin C

rec

makes accessible the output of the tone switch rectifier and provides a means of

controlling tone switch delays (mainly HB-LB). For correct operation of the IC, a capacitor and a
parallel connected resistor should be connected between this pin and ground. A capacitor of
100nF and resistor of 1MW will give a LB-HB delay of around 100

s and a HB-LB delay of 30ms.

The comparator circuit utilises no external components.

4-132

ZNBG3113
ZNBG3114

4-133

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.

ZNBG3113
ZNBG3114

ZNBG3113
ZNBG3114

Single Universal LNB Block Diagram

The following block diagram shows the main section of an LNB designed for use with the Astra
series of satellites. The ZNBG3113/14 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.

APPLICATIONS INFORMATION(cont)

Tone detection and band switching is provided on the ZNBG3113/14 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 F

enables one of two outputs, L

and

. A tone present enables H

and tone absent enables L

. The L

and H

outputs are designed

to be compatible with both MMIC and discrete local oscillator applications, selected by pin L

Referring to Figure 1 wiring pin L

to ground will force L

and H

to switch between -2.6V

(disabled) and 0V (enabled). Referring to Figure 2 wiring pin L

to a positive voltage source (e.g.

a potential divider across V

and ground set to the required oscillator supply voltage, V

OSC

) will

force the L

and H

outputs to provide the required oscillator supply, V

OSC

, when enabled.

Tone Detection Function

22kHz

Disabled

Enabled

-2.6 volts

Enabled

Disabled

-2.6 volts

OSC

22kHz

Disabled

Enabled

Note 1

OSC

Enabled

Disabled

OSC

Note 1

Note 1: 0 volts in typical LNB applications but ependent on extenal circuits.

4-134

ZNBG3113
ZNBG3114

Zetex plc.
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Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries)
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or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or
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