BYI datasheet Rev A
BYI-1
BYISTOR FOR LINEAR
POWER AMPLIFIERS
GENERAL DESCRIPTION
The BYI-1 is a semiconductor device specifically designed for use in linear
amplifier bias circuitry. The byistor acts as a low impedance D.C. bias source
which has two modes for thermal compensation.
CASE OUTLINE
BYI – 1
55FT
Supplier
FEATURES
•
•
•
•
The package can be physically attached to the same heatsink used for the
RF Power Transistors
Contains a diode fabricated like an RF Power Transistor (same material,
geometry and diffusion) which provides one mode of thermal tracking
Contains a silicon resistor which provides a second mode of thermal
tracking
Fabricated and assembled with the same consistency and precision used
in building RF Power Transistors.
Injector
Reference
BYISTOR SPECIFICATIONS
Maximum Injector Current I
j
= 500 mA
V
ir
= 0.85 +/- 0.03 ( I
j
= 350 mA, I
s
= 0, T
c
= 25
o
C)
Resistor = 0.70 +/- 0.12
Ω,
(T
c
= 25
o
C)
Maximum Temperatures
Storage Temperature
Operating Junction Temperature
- 65 to +150
o
C
+150
o
C
BYISTOR – A DEVICE FOR LINEAR AMPLIFIER BIAS NETWORKS
An essential part of any linear solid state amplifier is the D.C. Bias circuitry. The bias circuitry for class AB must meet all
of the following basic requirements:
•
Provide voltage/current capability compatible with the static (zero RF drive) collector current requirements of the
amplifier
•
Provide a low impedance voltage source with sufficient current capability to counter the negative rectification
effect of the RF drive on the base of the transistor
•
Compensate for the drop in the V
be
of the transistor as a function of increasing temperature (thermal tracking) to
eliminate the possibility of D.C. thermal runaway of the amplifier
Microsemi Corp. is delivering a semiconductor device called a BYISTOR, to be used as the key element in a transistor
bias network. The advantages of using a BYISTOR are the excellent temperature tracking for D.C. stability and the
significantly simplified bias circuit. Furthermore, supplemental emitter resistance is not needed to insure D.C. stability.
Jan 2009
Microsemi reserves the right to change, without notice, the specifications and information contained
herein. Visit our web site at
www.microsemi.com
or contact our factory direct.
BYI datasheet Rev A
BYI-1
The key elements of a BYISTOR are:
•
A diode fabricated like and RF power transistor (
same material, geometry, and diffusion process) for
improved temperature tracking;
•
An internal silicon resistor to further improve
temperature tracking;
•
A package that can be physically attached to the
same heatsink used for the RF amplifier transistor (
available in a variety of stud, flange or flangeless
packages)
Fig. 1 shows the basic design of a BYISTOR. By providing a
constant current to the injector terminal, the diode acts as a
voltage source with approximately 0.3Ω source impedance.
The addition of a silicon resistor (approximately 0.7Ω )
increases the apparent source impedance of the BYISTOR to
approximately 1
Ω.
The silicon resistor increases in resistance, and the diode
voltage decreases with increasing temperature. As a result, the
source impedance of the BYISTOR increases, and the bias
voltage decreases with increasing temperature (see Fig 2 & 3).
By mounting the package on the same heatsink as the RF
transistor, the BYISTOR will thermally track the transistor and
compensate for the reduction in V
be
. The result is improved
D.C. stability of the amplifier and elimination of D.C. thermal
runaway of the RF transistor..
Circuit Applications
To effectively use a BYISTOR , it should be mounted on the
same heastink and as physically close to the RF power
transistor as possible. Connect the bias circuit as shown in Fig.
4 for class AB operation. Provide approximately 350 mA form
any convenient voltage into the injector terminal. Then, adjist
R2 until the desired static collector current is achieved
(increasing R2 increases the V
be
and increases the static
collector current). No further effort is required. The bias circuit
using the BYISTOR will now:
*Provide the appropriate static collector current;
*Provide a low impedance D.C. voltage source
*Thermally track the RF transistor and compensate for
increasing temperatures, eliminating D.C. thermal runaway
problems.
Microsemi reserves the right to change, without notice, the specifications and information contained
herein. Visit our web site at
www.microsemi.com
or contact our factory direct.
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