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US 5,477,191 AGranted
Variable gain amplifier
AssigneeSGS-Thomson Microelectronics S.A.
InventorMarco Demicheli
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AssigneeSGS-Thomson Microelectronics S.A.
InventorMarco Demicheli
Estimating the term…
A temperature-stable variable gain amplifier having a differential input stage coupled to a first terminal of a voltage supply generator and a second terminal of the voltage supply generator through first and second field-effect transistors whose gate terminals are connected to two bipolar transistors which are also connected between the first terminal of the voltage supply generator, through two resistors, and the second terminal of the voltage supply generator, through third and fourth field-effect transistors. Also, the third and fourth transistors have gate terminals connected into a second common control terminal, and the collector terminals of the bipolar transistors form output terminals for the amplifiers.
A variable gain amplifier comprising first and second gain stages cascade connected between first and second terminals of a voltage supply generator, characterized in that the first gain stage comprises a differential stage coupled to the first terminal of the voltage supply generator and having first and second input terminals which form first and second input terminals for the amplifier, as well as first and second output terminals coupled to the second terminal of the voltage supply generator, respectively through first and second variable resistance load elements having a first common control terminal, and that the second gain stage comprises first and second transistors each having first and second terminals and a control terminal, the control terminals of said first and second transistors being respectively connected to the first and second output terminals of the differential stage, the first terminals of said first and second transistors being both coupled to the first terminal of the voltage supply generator and forming respectively a first output terminal and a second output terminal for the amplifier, the second terminals of the first and second transistors being both coupled to the second terminal of the voltage supply generator through respective first and second variable resistance circuit elements which are both connected to a second common control terminal.
A variable gain amplifier having a first input terminal and a second input terminal as well as a first output terminal and a second output terminal, said variable gain amplifier comprising:
Dependencies are inferred from the claim text.
Drawings are temporarily unavailable. Open the PDF at USPTO
No related US applications are recorded in the indexed filing history.
The device being at least one of the amplifying solid-state elements: using field-effect transistors [FET]
Details of arrangements for controlling amplification: modifications of control circuit to reduce distortion caused by control
Control of amplification
Term ended 30 Jun 2014 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to variable gain amplifiers (VGA), and in particular to a VGA whose gain is dependent essentially on a control voltage and can be temperature stabilized.
In many applications--e.g. automatic gain control (AGC) systems in audio and TV apparatus--the signals whose amplitudes may vary within a wide range need to be amplified so that an amplified signal with constant amplitude can be presented at the output.
In such automatic gain controls as usually comprise at least one variable gain amplifier in a loop structure, a signal level detector, a control current generator driven by the signal level detector, and a stabilizing capacitor, it is indeed the variable gain amplifier that constitutes the most critical part of the arrangement.
The features and advantages of an amplifier according to the invention will become apparent from the following description of an embodiment thereof, given by way of example and not limited by the accompanying drawings.
In the drawings:
FIGS. 1 and 2 show circuit diagrams for variable gain amplifiers of known types;
The circuit diagram of FIG. 3 comprises first and second cascade-connected gain stages which constitute the core portion of a variable gain temperature-stabilized amplifier according to the invention.
The first gain stage includes a differential input stage coupled to a first terminal +Vcc of a voltage supply generator through a constant current generator G1 and comprising two transistors Q21, Q22 and two resistors R1,
The control terminals of the transistors are the amplifier input terminals IN+ and IN-.