Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1996-03-29
2002-08-13
To, Doris H. (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S003020, C455S131000
Reexamination Certificate
active
06434374
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a down converter of a communications receiver and, more particularly, to apparatus for dynamically controlling the conversion gain of a down converter.
BACKGROUND OF THE INVENTION
In a microwave distribution system for digital television signals, the television signals are transmitted on radio frequency (RF) carrier signals in the L-band microwave frequency range (e.g., 2150 to 2686 MHz). A highly directive dish-like antenna of a receiving system receives the microwave signals transmitted by the television signal transmitter. A low noise block (LNB) converter converts the entire range (“block”) of relatively high frequency microwave signals transmitted by the transmitter to a more manageable lower range of frequencies (e.g., 128 to 408 MHz). This process is known as “down conversion”. Typically, the LNB converter is part of an outdoor unit which includes the dish-like receiving antenna and the LNB converter. The receiving system also comprises an indoor unit. The RF signals from the outdoor unit are coupled through a coaxial cable to the indoor unit. The indoor unit includes a tuner for selecting the RF signal corresponding to a desired channel from the RF signals received from the LNB converter and for converting the selected RF signal to an even lower intermediate frequency (IF) signal. The indoor unit also includes a signal processing section for demodulating and decoding the IF signal. The RF signals produced by the LNB converter are sometimes referred to as “first IF” signals, and therefore the IF signal produced by the tuner is sometimes referred to as a “second IF” signal.
Typically, there is a single transmission site for all of the microwave signals which are received by the outdoor unit. As such, the distance from that transmission site to the receiving antenna generally determines the signal strength of all of the RF signals received by the outdoor unit. In some instances, where the receiver is relatively near to the transmitter site, the received RF signals may overload the LNB converter and the resulting distortion products may degrade the performance of the indoor unit. In a digital television transmission system, in which television information is encoded in digital form, such an overload may cause decoding errors within the signal processing section of the indoor unit. Such decoding errors are often catastrophic in that they may cause a total loss of television image and audio information.
To alleviate this problem, receiver installation technicians are instructed, when installing the system, to use a relatively low gain antenna (e.g., 20 dB gain) when the receiving location is near to a transmitter site and use a relatively high gain antenna (e.g., 24 dB gain) when the receiving location is far from the transmitter site (e.g., 30 miles or more). However, even with a low gain antenna, an overload of the LNB converter may occur. Thus, technicians are also instructed to use a LNB converter with a relatively low conversion gain for installations which are near the transmitter site. Generally, an installation technician can select one of two LNB converters having either a 20 dB or a 30 dB conversion gain.
Such an equipment selection process has been found to be error prone. For example, if the technician has incorrectly selected an antenna and LNB converter combination for a particular site, an optimal signal level, avoiding the extremes of too weak a signal and signal overload, may not be provided. Consequently, the indoor unit may produce decoding errors resulting in video and audio dropouts.
SUMMARY OF THE INVENTION
Therefore, it has been recognized by the applicant that a need exists in the art for a LNB converter containing automatic gain control (AGC) circuitry which adjusts the conversion gain of the LNB converter to compensate for variation in the received signal strength. Accordingly, the present invention concerns apparatus for dynamically controlling the conversion gain control of a down converter such as a LNB converter included in an outdoor unit.
More particularly, a low noise block (LNB) converter incorporating the invention comprises a gain controlled RF amplifier, a conversion stage including a mixer and a local oscillator, and an output amplifier, and a gain control signal generator which responds to the output signal of the output amplifier to produce a gain control signal. The gain control signal is applied to the gain controlled RF amplifier such that the gain of the amplifier is substantially constant for input signal levels above a predetermined threshold.
In one embodiment, the entire automatic gain control apparatus is totally included within the outdoor unit.
In another embodiment of the invention, portions of the gain control apparatus are partially included in the outdoor unit and partially included in the indoor unit. More specifically, the gain control signal generator is included in the indoor unit of the receiving system. The gain control signal generated by the gain control signal generator is coupled through a transmission path to the outdoor unit of the receiver system. For example, the transmission path may comprise the center conductor of the coaxial cable which connects the outdoor unit to the indoor unit. To facilitate transmitting the control signal on a single conductor such as the center conductor of the coaxial cable, an encoding apparatus is included in the indoor unit to modulate a signal carried by the single conductor with gain control information. For example, the gain control signal may be converted to a frequency modulated low frequency tone which is coupled to the center conductor of the transmission line. The center conductor is coupled to a tone decoder within the outdoor unit which regenerates the gain control signal for controlling the gain of the RF amplifier. Alternatively, the magnitude of the supply voltage for the LNB converter which is typically carried to the LNB through the center conductor of the coaxial cable may be modulated by the gain control signal.
REFERENCES:
patent: 3259846 (1966-07-01), Elliott et al.
patent: 4158113 (1979-06-01), Lacroix
patent: 4205269 (1980-05-01), Watanabe
patent: 4237490 (1980-12-01), Harford
patent: 4520507 (1985-05-01), Moon
patent: 4553105 (1985-11-01), Sasaki
patent: 5175882 (1992-12-01), Higashijima
patent: 5313220 (1994-05-01), Hemmie et al.
patent: 5408698 (1995-04-01), Serizawa et al.
patent: 5434537 (1995-07-01), Kukkonen
patent: 5649311 (1997-07-01), Somei
patent: 5659892 (1997-08-01), Soleimani et al.
patent: 2000167 (1990-04-01), None
Document entitled, Additional Comments and Summary of Duel Carrier 2-for-1 System, RCA Review, vol. 41, Sep., 1980.
European Search Report citing the above-listed reference AA.
Akiyama Kuniyuki
Thomson Licensing S.A.
To Doris H.
Tripoli Joseph S.
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