Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1998-10-27
2001-05-22
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S254000
Reexamination Certificate
active
06236268
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an amplifier comprising a first and a second transistor arranged as a differential pair, each transistor having a bias terminal, a reference terminal connected to a current source and a transfer terminal connected to a supply terminal via a resistive branch, the bias terminals and the transfer terminals of the first and second transistors forming, respectively, a differential input and output, which are intended to receive and supply an input voltage and an output voltage respectively, a ratio between the values of the AC components of said voltages defining the gain of the amplifier.
BACKGROUND OF THE INVENTION
Such an amplifier, often called differential amplifier, is currently used in the integrated circuit industry. It is notably described in the title “Analysis and Design of Analog Integrated Circuits” by Messrs. Gray and Meyer. The gain and the maximum amplitude of the output voltage of this differential amplifier are both proportional to the product of the value of the impedance of the resistive branches and the value of the current supplied by the current source, called bias current. In certain applications, particularly radio signal receiving or processing applications in which the reduction of any form of noise which may affect the processed signals is an essential priority, this amplifier has for its function to perform both an amplification of a sinusoidal input voltage and its transformation into a square-wave output voltage. Such a transformation enables to avoid that the amplification introduces an additional noise component in the output voltage, which noise component is linked with the instantaneous value of the input voltage. Nevertheless, this transformation requires to have a high gain, so that the output voltage has edges which have such a steepness that the transitions they represent are well defined with time. This may be obtained by choosing a large value for the impedance of the resistive branch. Such a solution, however, has a major drawback: the effect of it is that the value of the maximum amplitude of the output voltage is increased considerably, which may provoke the saturation of circuits intended to receive said voltage and thus considerably disturb the operation of the system integrating the amplifier, which is unacceptable.
It is an object of the present invention to remedy this drawback to a large extent by proposing an amplifier whose gain and maximum value of the amplitude of the output voltage may be controlled independently of each other.
SUMMARY OF THE INVENTION
Indeed, an amplifier as defined in the opening paragraph is characterized according to the invention in that the resistive branches of the first and second transistors have each at least one intermediate terminal between a first and a second resistive element arranged in series, and in that each resistive branch is provided with a first element which permits the conduction of a current controlled by the potential of its intermediate terminal to its associated transistor when the latter is conductive, and with a second element which permits the conduction of a current to the other transistor of the differential pair when said other transistor is conductive.
In such an amplifier, the choice of a considerable resistance for the first resistive element will result in a high gain allowing a proper transformation of a sinusoidal input voltage into a square-wave output voltage, whereas a suitable choice of the resistance of the second resistive element will enable to limit the maximum amplitude of the output voltage to such a value that said voltage will be incapable of causing the circuits which are intended to receive the output voltage to be saturated.
In one of its embodiments, advantageous by the simplicity of its structure and the saving on components that is the result thereof, an amplifier according to the invention is characterized by claim
2
.
The claims
3
and
4
offer particular embodiments of an amplifier according to the invention.
As explained above, an amplifier as described above may be advantageously utilized for processing radio signals. The invention thus also relates to a radio telephony device as claimed in claim
5
.
REFERENCES:
patent: 4864248 (1989-09-01), Jansen
patent: 6163235 (2000-12-01), Klemmer
By Messrs. Gray and Meyer, “Analysis and Design of Analog Integrated Circuits” pp. 228-229.
Halajian Dicran
Mottola Steven J.
U.S. Philips Corporation
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