znbg2001 Zetex Semiconductors plc., znbg2001 Datasheet - Page 4

• Manufacturer Part Number: znbg2001
• Description: Fet Bias Controller
• Manufacturer: Zetex Semiconductors plc.

FUNCTIONAL DIAGRAM
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 ZNBG2000/1 contains 2 such
stages.
The drain voltage of the external FET Q
ZNBG device to its normal operating voltage. This is
determined by the on board V
ZNBG2000 this is nominally 2.2 volts whilst the
ZNBG2001 provides nominally 2 volts.
ZNBG2000
ZNBG2001
D
Set reference, for the
N
is set by the
7
4
The drain current taken by the FET is monitored by
the low value resistor I
the gate of the FET adjusts the gate voltage of Q
that the drain current taken matches the current
called for by an external resistor R
devices have the facility to program different drain
currents into selected FETs.
Since the FET is a depletion mode transistor, it is
usually 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
NB
and C
SUB
D
Sense. The amplifier driving
.
ISSUE 1 - AUGUST 2001
CAL
FUNCTIONAL
. Both ZNBG
N
so