Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
1998-07-30
2001-05-01
Shingleton, Michael B. (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S12400D, C330S12400D, C330S295000
Reexamination Certificate
active
06225865
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns an antenna switching system including a switching circuit for switching among the antennas which have different directivities.
BACKGROUND OF THE INVENTION
For reception of television and other broadcast signals, it is usually preferable to have an antenna with some directivity to discriminate undesirable multipath signals. Such a directional antenna can be rotated mechanically toward a broadcast transmitter. However, the mechanical rotation is undesirable since it requires additional costly rotating equipment. Another way of directing the antenna is to select one of the fixed antennas, which is originally oriented toward a desired transmitter. The notion of switching between different antennas is well described in S. Takeda et al. “FM Mutlipath Distortion in Automobile Receivers Has Been Significantly Reduced by A New Antenna System” pp. 263-269
IEEE Transaction on Consumer Electronics,
Vol. CE-26, August 1980. More specifically, this article discloses a switching antenna system including the two loop antennas orthgonally combined. Once multipath interference occurs for one loop antenna being used, the multipath distortion sensor will detect it and a user can switch for the alternative.
As for antenna switching circuits, many arrangement have been proposed. One of such arrangements is described in U.S. Pat. No. 4,959,873 granted to Flynn et al. In Flynn et al., a signal output line is switched to one of two or more input lines to which it is permanently connected at a common junction. Each input line has an associated amplifier stage which can be biased in a normal high gain (“on”) state, or in an isolation (“off”) state. Biasing in the “off” state causes that the amplifier stage output presents a low impedance to its own input line, the length of which is chose to reflect a high impedance at the junction with the other lines. This switching arrangement enables the return loss and insertion loss of the “on” path to be kept to low values while simultaneously offering a high insertion loss to the “off” path signals. However, this arrangement is undesirable especially for switching VHF/UHF signals since it requires a particular length of the input line which could significantly limit design freedom for the circuitry. Therefore, a need exists for an RF switching arrangement that provides acceptable isolation for the “off” signals in VHF/UHF bands of frequencies without demanding an additional attenuation circuit.
SUMMARY OF THE INVENTION
The present invention solves the described problem by providing a switching circuit comprising: an amplifier for amplifying an input signal, switching means for coupling the amplified signal to an output, means responsive to a first state of a control signal for simultaneously causing the switching means to be in a conductive state and enabling the amplifier for amplifying the input signal, and the means responsive to a second state of the control signal for simultaneously causing the switching means to be in a non-conductive state and removing an DC operating voltage from the amplifier for further isolating the input signal from the output.
REFERENCES:
patent: 4521810 (1985-06-01), Nigborowicz et al.
patent: 4677688 (1987-06-01), Yoshihara et al.
patent: 4903334 (1990-02-01), Anderson
patent: 4959873 (1990-09-01), Flynn et al.
patent: 5045733 (1991-09-01), Sendelweck
patent: 5117123 (1992-05-01), Sendelweck
patent: 5475875 (1995-12-01), Katsuyama et al.
patent: 5530923 (1996-06-01), Heinonen et al.
patent: 700169 (1997-02-01), None
patent: 92/22937 (1990-09-01), None
Akiyama Kuniyuki
Shingleton Michael B.
Thomson Licensing S.A.
Tripoli Joseph S.
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