ZNBG3115Q20 ZETEX [Zetex Semiconductors], ZNBG3115Q20 Datasheet - Page 7

• Manufacturer Part Number: ZNBG3115Q20
• Description: FET BIAS CONTROLLER WITH POLARISATION SWITCH AND TONE DETECTION
• Manufacturer: ZETEX [Zetex Semiconductors]

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 ZNBG3115/16 contains 3 such stages. The negative rail generator is common to both
devices.
The drain voltage of the external FET Q
determined by the on board V
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
external resistor R
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
ISSUE 1 - JUNE 2001
NB
and C
CAL
.
SUB
.
D
Set reference, for the ZNBG3115 this is nominally 2.2 volts whilst the ZNBG3116
N
N
so that the drain current taken matches the current called for by an
is set by the ZNBG device to its normal operating voltage. This is
7
ZNBG3115
ZNBG3116