Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
1999-11-26
2001-07-24
Shingleton, Michael B. (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S12400D, C330S254000, C330S285000
Reexamination Certificate
active
06265936
ABSTRACT:
BACKGROUND OF THE INVENTION
In the field of telecommunications, there is frequently a need to deactivate two amplifier stages alternately. In order to do this, the amplifier stages are usually triggered in push-pull mode over separate control lines. Such control lines allow the undesired coupling-in of interference in the amplifier stages and in following circuit elements, particularly in high-frequency applications.
SUMMARY OF THE INVENTION
The object of the invention is to provide an amplifier arrangement with two alternately deactivatable amplifier stages which can be manufactured economically and have a high degree of immunity to high-frequency interference.
This task is solved by the features in patent claim 1. Advantageous embodiments and developments ensue from the subclaims.
The invention is based on the recognition that amplifier stages can be switched into an inactive state through a low-resistance connection of their amplifier inputs to a reference potential connection, i.e. by short-circuiting the amplifier inputs to the reference potential. According to the invention, two amplifier stages, each with an amplifier input, and a switching stage over which the amplifier inputs of the amplifier stages are linked to one another, are integrated in a switching circuit to form an integrated amplifier arrangement. In the case of this amplifier arrangement, the amplifier input of the second amplifier stage is low-resistance linked to the reference potential connection via the switching stage according to a first input voltage available at the amplifier input of the first amplifier stage, preferably according to the d. c. voltage working point of the first input voltage, and thereby short-circuited to a reference potential, for example to a ground potential. The second amplifier stage is deactivated in this way.
The amplifier input of the second amplifier stage is preferably short-circuited to the reference potential if the first input voltage has a d. c. voltage working point with which the first amplifier stage is activated, i.e. if the amplifier input of the first amplifier stage is not short-circuited via external switching means to reference potential and the d.c. voltage working point of the first input voltage is thereby greater than a defined switching threshold. If, on the other hand, the amplifier input of the first amplifier stage is short-circuited to reference potential, then the d.c. voltage working point of the first input voltage lies below the defined switching threshold and the first amplifier stage is thereby deactivated. In this case, the amplifier input of the second amplifier stage is decoupled from the amplifier input of the first amplifier stage, i.e. the deactivation of the second amplifier stage is canceled.
The significant advantages of the amplifier arrangement according to the invention lie in the fact that no separate connections are required for alternately deactivating the amplifier stages, that the switching stage can be manufactured with a small number of components which can be integrated in a simple manner—the short-circuiting of the amplifier input of the second amplifier stage is preferably achieved via a switch, realized as a field-effect transistor for example—, that it has small dimensions on account of the low number of connections and circuit elements and therefore requires little space on a printed circuit board, and that it can be wired with a small number of lines, which represents an important advantage, particularly in high-frequency applications, for example in television tuners, because a short wiring routing is possible on account of the low number of external lines, through which the coupling-in of high-frequency interference is avoided.
In an advantageous development of the amplifier arrangement according to the invention, the switching stage can also be triggered via the amplifier input of the second amplifier stage—for this purpose the switching stage preferably has a further switch realized as a field-effect transistor—so that the amplifier input of the first amplifier stage is short-circuited to reference potential via the switching stage according to the d.c. voltage working point of a second input voltage available at the amplifier input of the second amplifier stage. The user then has the option to select that one of the amplifier inputs for deactivating the amplifier stages which, given the wiring of the amplifier arrangement, enables the shortest possible wiring routing and without or with the least possible number of crossings.
In an advantageous embodiment of the amplifier arrangement, each of the two amplifier stages has an amplifier transistor realized as a field-effect transistor which is operated in common source mode, and which preferably has two gate electrodes, of which the first is linked to the amplifier input of the respective amplifier stage and the second is linked to an automatic gain control connection over which the amplification or transconductance of the respective amplifier transistor can be controlled. The significant advantage of the amplifier transistors operated in common source mode lies in the fact that these are disabled when the amplifier inputs are short-circuited, so that no current flows in the amplifier stages in the deactivated state.
The amplifier arrangement is best suited for use in high-frequency circuits, particularly in television tuners in which one of two input signals with different frequencies is selected for further processing and in each case one of two signal branches matched to the frequency of the input signals is amplified.
REFERENCES:
patent: 3525050 (1970-08-01), Wolf et al.
patent: 4631490 (1986-12-01), Takahashi
patent: 4829263 (1989-05-01), Gulczynski
patent: 5008631 (1991-04-01), Scherer et al.
patent: 5621353 (1997-04-01), Botti et al.
patent: 6160447 (2000-12-01), Huang
patent: 2 289 810 (1995-11-01), None
Heigl Franz
Wicha Axel
Kunitz Norman N.
Shingleton Michael B.
Venable
Vishay Semiconductor GmbH
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