For price, delivery and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824

Phone: 978-250-3343

Fax: 978-250-3373

Order On-line at www.hittite.com

Application Support: Phone: 978-250-3343 or apps@hittite.com

12

HMC980

v00.0312

Active BiAs controller

High current

Application Notes

Detailed Description

all amplifiers require stable quiescent current to operate at their specifications. Many amplifiers in the market require

external biasing to achieve stable quiscent current. hMC980 is a fully integrated biasing solution for such amplifiers.

With an internal feedback, the automatic gate voltage control achieves constant quiescent bias through the amplifier

under bias, independent of temperature and amplifier threshold variations. the quiescent current is adjusted with

a resistor connected externally. the hMC980 employs an integrated control circuitry to manage safe power-up

and power-down sequencing of the targeted amplifier. the hMC980 can provide auto-bias solution to virtually any

amplifier in the market (both enhancement and depletion type) with a quiescent current of up to 1.6a and a supply

voltage of up to 16.5V.

the hMC980 has an integrated negative voltage generator to create negative voltages required to drive depletion

mode amplifiers. if an external negative supply is already available or an enhancement mode device is targeted, the

negative voltage generator can be disabled.

the hMC980 achieves excellent bias stability over supply and temperature variations. the gate control can both sink

and source current (±4 ma) which is required to compensate for charging gate current of the amplifier over input power

variations. the hMC980 also generates a second gate voltage VG2. VG2 can be adjusted through a resistor divider

connected to VDD for the amplifiers which require second gate voltage.

the hMC980 ensures safety of the external amplifier during turn on/off by automatically adjusting the sequence of

VDrain, VGate and VG2 outputs.

the hMC980 has a built-in over-under current alarm feature. if a fault conditions arises (either under or over current)

an alarm signal is generated (alM, active hiGh). the current alarm signal provided in hMC980 does not affect the

operation of the controller. it is included for monitoring purposes where a system level protection can be implemented

with external control circuitry.

the hMC980 employs s0, s1 pads to control rDs_on resistance of the internal switch between VDD and VDrain.

refer to the section under the “supply and Drain Voltage” section for details.

the hMC980 has a built-in self protection feature to protect itself against short circuit conditions at the VDrain

output. the hMC980 has also a built-in VneG fault protection feature to protect both itself and the amplifier under

bias against short circuit conditions at the VneG pad.

Digital Power supply (vDiG)

the hMC980 requires an external low voltage bias rail (3.3V to 5.0V). VDiG powers the internal logic circuitry. VDiG

draws and average of 3.5 ma from a 3.3V. VDiG can accept voltages up to 5.0V.

supply and Drain voltage (vDD and vDrAin)

the VDD supply to the hMC980 is directly connected to the VDrain output through an internal MosFet switch. this

internal MosFet is controlled through power-up sequencing which ensures that no voltage is applied to the drain of

the external amplifier until the gate voltage is pulled down to VneG (ensuring external amplifier is pinched-off). the

VDrain output of the hMC980 should be connected to the drain (collector) of the amplifier under bias for the active

bias control feedback and power-up/down sequencing to operate properly.

there will be a voltage drop from VDD to VDrain due to finite rDs_on resistance of the internal switch. to

compensate for this voltage drop choose the VDD value as shown in equation (1).

VDD = VDrain + iDrain x rDs_on

(1)