The unibi functional block - A monolithic amplifier with unipolar-bipolar structure

In solid state circuits, it is often necessary to transform from high to low impedance levels without power loss. Conventional techniques usually involve the use of matching transformers which are costly in both money and space, or of degenerative circuits which introduce considerable loss of gain. A functional block has recently been designed and fabricated on a single crystal silicon block which provides the necessary matching with power gain over a limited frequency range. Another advantage of the block is that it is truly unilateral over this frequency range, requiring no neutralization to make the output independent of the input. Many cases arise where the block can be directly coupled to the previous stage without capacitors or other coupling components. The functional block consists of two active regions. The input region operates as a field effect transistor, while the output region consists of a conventional bipolar transistor. Both active regions are processed simultaneously using standard photo masking techniques. The input of the block can be represented by a parallel resistor and capacitor, equivalent to a reverse biased diode (ordinarily about 2-5 megohms in parallel with 5-10 pfd), giving a very high input impedance over the frequency range. With the present design, the block is capable of 40-50 db power gain at current levels of 2-5 ma. The overall transconductance is 5000 to 10,000 mhos, and the open circuit voltage gains are greater than 20.