Pseudo bipolar junction transistor

Details Pseudo bipolar junction transistor Pseudo bipolar junction transistor

2000-05-08

2001-11-27

Callahan, Timothy P. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Gating

Utilizing three or more electrode solid-state device

C327S543000, C327S427000

Reexamination Certificate

active

06323719

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a bipolar junction transistor, and more particularly to a pseudo bipolar junction transistor using CMOS process.
2. Description of the Related Art
Variable grain amplifiers, auto-gain controllers, transfer linear function signal processors and recently-developed logarithmic filters and logarithmic current control oscillators are significantly applied in various fields. There is a common point for those circuits that bipolar junction transistors (BJTs) having an exponential function are used. Although in CMOS process, lateral transistors and MOS transistors operating in weak inversion region can be used for replacement, their application fields are limited due to their poor performances. Therefore, in many fields, BJTs can not be replaced with MOS transistors.
For variable gain amplifier and auto-gain controller applications, several pseudo-exponential circuits designed according to CMOS technology has been successfully developed. However, due to their complicated structures, the pseudo-exponential circuits can not function as BJTs. Therefore, CMOS transistors operating in saturation region are used to replace BJTs. The reason how come does the CMOS transistors operate in saturation region is that MOS transistors in weak inverse region has a narrow operation region, poor frequency response and poor match effect. Furthermore, lateral transistors have a small collector-base current gain and a larger leakage current. Consequently, making MOS transistors operate in saturation region has a valuable application.
SUMMARY OF THE INVENTION
In view of the above, the invention provides a pseudo bipolar junction transistor circuit which is performed by CMOS transistors operating in saturation region. The pseudo bipolar junction transistor circuit according to the invention has a simple structure, being able to function as a single bipolar junction transistor. Therefore, variable gain amplifiers, transfer linear function signal processors and logarithmic filters and oscillators can be realized using the inventive pseudo bipolar junction transistor. Moreover, the principle for designing various circuits using the inventive pseudo bipolar junction transistor is the same as that using the general bipolar junction transistor. Therefore, bipolar junction transistors used in original circuits can be directly replaced by the inventive pseudo bipolar junction transistors, with an appropriate bias current selected. Therefore, in intermediate frequency applications and designs, BiCMOS process can be replaced with CMOS process, thereby simplifying the requirements of process.
In order to attain the above-stated objects, a pseudo bipolar junction transistor according to the invention includes two MOS transistors operating in saturation region. The two MOS transistors are electrically connected in parallel with their drains and sources functioning as a collector and a emitter of the pseudo bipolar junction transistor, respectively, a first gate without any signal inputted and a second gate functioning as a base of the pseudo bipolar junction transistor, wherein the two gates are supplied with the same DC bias.
The pseudo bipolar junction transistor further includes two identical squares. The two identical squares are electrically connected to the two MOS transistors in series, having the same bias, one without any signal inputted and the other with a signal inputted. The outputs of the two identical squarers are added to each other to generate a pseudo exponential function, and then the pseudo exponential function is expanded into a Tyler series with the terms over two order omitted.
Furthermore, the pseudo bipolar junction transistor includes a constant current source and a PMOS transistor. One terminal of the constant current source is electrically connected to the source of the PMOS transistor, and the gate of the PMOS transistor is electrically connected to the sources of the MOS transistors to prevent constant DC bias from being affected by variation of the source voltage.
The pseudo bipolar junction transistor further includes a first PMOS transistor, a second PMOS transistor, a third PMOS transistor and a four PMOS transistor. The gates of the first PMOS transistor and the second PMOS transistor are electrically connected to the sources of the MOS transistors, the source of the third PMOS transistor is electrically connected to the drain of the first PMOS transistor and the source of the four PMOS transistor is electrically connected to the drain of the second PMOS transistor.
According to the invention, the pseudo bipolar junction transistor has a characteristic equation similar to that of a general bipolar junction transistor. The pseudo bipolar junction transistor can easily replace the general bipolar junction transistor for applications in variable gain amplifiers, auto-gain controllers, transfer linear function signal processors and recently-developed logarithmic filters and logarithmic current controlled oscillators. The pseudo bipolar junction transistor is manufactured by CMOS process instead of BiCMOS process.


REFERENCES:
patent: 5469076 (1995-11-01), Badyal et al.
patent: 5793239 (1998-08-01), Kovacs et al.
patent: 5796281 (1998-08-01), Saeki et al.
patent: 5801584 (1998-09-01), Mori
patent: 5801586 (1998-09-01), Ishizuka
patent: 5966032 (1999-10-01), Elrabaa et al.

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