Amplifiers – With semiconductor amplifying device – Including plural stages cascaded
Reexamination Certificate
1999-10-28
2001-06-12
Lee, Benny (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural stages cascaded
C330S098000
Reexamination Certificate
active
06246290
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high frequency amplifier circuits, and in particular, to high frequency amplifier circuits driven by a current signal source and providing high current gain.
2. Description of the Related Art
Referring to
FIG. 1
, cascode amplifiers (i.e., transistor Q
2
, driving by transistor Q
1
, in turn, drives transistor Q
3
in a cascode configuration) are often used for video amplifier designs due to their ability to provide a high frequency signal response while also providing a moderate amount of voltage gain. For example, in a typical open loop cathode ray tube (CRT) video driver application, a cascode pair (transistors Q
2
and Q
3
) can be driven by an emitter follower circuit (transistor Q
1
and resistor R
1
) to create an amplifier with a high input impedance and a voltage gain in the range of
10
-
15
.
However, some applications require significantly higher signal gains. In such applications, it is also sometimes necessary to operate with a differential input signal so as to minimize DC offsets, drift and noise. In still other applications, it may further be desirable for such a high bandwidth amplifier to receive its input signal in the form of a current signal.
SUMMARY OF THE INVENTION
A high gain, current driven amplifier uses an emitter follower circuit with another emitter follower circuit connected in a feedback configuration to drive a common base amplifier circuit in place of a conventional cascode amplifier configuration to achieve a high frequency response with adequate signal gain. A differential input signal can be used, thereby minimizing input DC offsets, drift and noise, by using a differential amplifier to convert a differential input signal voltage to the input signal current for driving the emitter follower circuits. The current gain is determined by a ratio of the resistances in the emitter circuits of the emitter follower circuits.
In accordance with one embodiment of the present invention, a current driven amplifier includes amplifier input and output terminals and voltage follower amplifier circuits. The amplifier input terminal is configured to convey an amplifier input current, while the amplifier output terminal is configured to convey an amplifier output current which is a multiple of the amplifier input current. A first voltage follower amplifier circuit includes a first bias terminal, a first input terminal coupled to the amplifier input terminal, and a first output terminal coupled to the amplifier output terminal, and is configured to provide a first portion of the amplifier output current. A second voltage follower amplifier circuit includes a second bias terminal, a second input terminal coupled to the amplifier output terminal, and a second output terminal coupled to the amplifier input terminal, and is configured to receive a portion of the amplifier input current and provide a second portion of the amplifier output current.
In accordance with another embodiment of the present invention, a current driven amplifier includes input and output terminals, two transistors and two resistors. The input terminal is configured to convey an input current, while the output terminal is configured to convey an output current which is a multiple of the input current. The first transistor includes a first base terminal coupled to the input terminal, a first emitter terminal and a first collector terminal. The second transistor includes a second base terminal coupled to the output terminal, a second emitter terminal and a second collector terminal. The first resistor is coupled between the first emitter terminal and the output terminal. The second resistor is coupled between the second emitter terminal and the input terminal.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.
REFERENCES:
patent: 4218659 (1980-08-01), Arai
patent: 5045808 (1991-09-01), Taylor
patent: 5530405 (1996-06-01), Rydel
Mills Thomas
Morrish Andrew
Baker & McKenzie
Choe Henry
Lee Benny
National Semiconductor Corporation
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