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HMC920LP5E
v07.1013
ACTIVE BIAS CONTROLLER
Application Notes
Detailed Description
HMC920LP5E is an active bias controller which can be configured to provide the supply voltage and adjust the
gate voltage of an external amplifier to achieve constant bias current. It can be used to bias both enhancement and
depletion type amplifiers. The HMC920LP5E achieves excellent bias stability over supply and temperature variations.
The gate control can both sink and source current (? mA) to achieve constant bias current over input power variations.
The HMC920LP5E standard application circuit generates 3.5V digital supply voltage (VDIG) for internal use, and
-2.5V negative voltage (VNEG) for depletion mode devices. If an external negative supply is already available or an
enhancement mode device is targeted, the negative voltage generator can be disabled.
HMC920LP5E controls the bias current of the external amplifier with the gate control block. The current passing
through the external amplifier is sampled and is used to control the VGATE voltage connected to the gate of the external
amplifier to achieve constant quiescent bias through the external amplifier. This active bias control continuously
adjusts the VGATE voltage to achieve constant bias current through the targeted amplifier independent of supply,
temperature, process variations, and threshold shifts due to aging.
HMC920LP5E   ensures   safety   of   the   external
amplifier   during   turn   on/off   by   adjusting   the
sequence of VDRAIN and VGATE outputs. The
current passing through the external amplifier is
monitored continuously. If a fault conditions arises
(either under or over current) an alarm signal is
generated (CURALM, active HIGH). A different alarm
signal is generated (VddALM, active LOW) if the
HMC920LP5E supply voltage drops below a certain
threshold. Both supply voltage and current alarm
signals provided in HMC920LP5E does not affect the
operation of the controller. Both alarms has designed
for   monitoring   purposes   where   a   system   level
protection can be implemented with external control
circuitry. The HMC920LP5E has power foldback and
short circuit protection features.
The HMC920LP5E is a system on chip solution for
the biasing needs of RF amplifiers and it has several
functional blocks (see functional block diagram on
the first page), to achieve the features summarized
above. Refer to the section of the specific functional
block for the detailed operation and adjustment
descriptions.
Typical Application Diagram