BYI datasheet Rev A

Microsemi reserves the right to change, without notice, the specifications and information contained

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 0.3

Ω source impedance.

The addition of a silicon resistor (approximately 0.7

Ω )

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

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

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.

BYI-1