AN-0002 Datasheet, PDF (3/6 Pages) ANADIGICS, Inc – Biasing Circuits and Considerations for GaAs MESFET Power Amplifiers

AN-0002
these transistors be well matched, operating at the same bias, and in the same thermal environment.
The schematic of Figure 3 is a refinement of the basic circuit that incorporates temperature compe nsation
as well as several other features. The user does not need to implement all of the functions, but they are
shown here for illustrative purposes.
The main features of this circuit are:
• Constant Operating Current
• Reduction of Part -to-Part Variation
• Temperature Compensation
• Negative Voltage Generator
• Power Sequencing (Negative before positive)
Positive
Supply
Q3
R1
R3
R5
Vdd
Q1
Q2
DUT
Vgg
R2
R4
+5V
ON/OFF
CONTROL
+5V
U2
MAX881R
C2
C1+
IN
C1
C1-
NC
C3
NEG OUT GND
/POK
OUT
C4
/SHDN
FB
Figure 3. Schematic for a Negative Bias Generator.
The Maxim MAX881 voltage inverter is shown in its standard configuration. This provides the negative
voltage necessary for the gates of the amplifier. The Maxim part works from supply voltages (V) of 2.5 to
05/2003
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