Satellite broadcasting converter, control circuit incorporated therein, and detector circuit used in such control circuit
View Patent ↗In a broadcasting satellite converter adapted to be connected to a BS tuner and fed with a power supply voltage signal from the broadcasting satellite tuner, a receiver circuit is controlled by a control circuit. The broadcasting satellite converter comprises a receiver circuit including a mixer, and a plurality of local oscillators connected to the mixer to convert broadcasting satellite signals into intermediate frequency signals, and a control circuit that controls the receiver circuit. The control circuit includes a detector circuit that detects whether a band switching pulse signal is superimposed on the pulse signal, the detector circuit including a converting circuit that converts a frequency of the band switching pulse signal into an integrated value for the detection of the band switching pulse signal. The control circuit further includes a selector circuit that selectively drives one of the local oscillators in accordance with the integrated value obtained in the detector circuit.
1. A switching circuit for a broadcasting satellite converter wherein two local oscillators having different oscillation frequencies are switched in accordance with whether a band switching pulse signal having a given frequency is superimposed on a power supply voltage transmitted from a broadcasting satellite tuner, said switching circuit comprising:
a monostable multivibrator circuit to which said power supply voltage is input from said broadcasting satellite tuner, and in which input pulses are converted into pulses having a given time width;
a first integrating circuit which integrates an output of said monostable multivibrator circuit to output a signal having a level corresponding to a duty factor of the output of said monostable multivibrator circuit;
a determining circuit having a delay circuit to which the output of said monostable multivibrator circuit is input, and determining whether an output of said first integrating circuit falls within a given range at a timing of an output of said delay circuit; and
a driver circuit which drives a local oscillator having an oscillation frequency corresponding to an output of said determining circuit.
2. The switching circuit as set forth in claim 1 , wherein said determining circuit includes first and second comparators which compare the output of said first integrating circuit with respective high and low limit reference voltages of said given range, first and second latch circuits which latch and output respective outputs of said first and second comparators at the timing of the output of said delay circuit, and a logic circuit which outputs a binary signal in accordance with whether the output of said first integrating circuit falls within said given range.
3. The switching circuit as set forth in claim 1 , wherein said determining circuit includes a comparator featuring a window-type comparison characteristic, to which the output of said first integrating circuit is input, and a latch circuit which latches and outputs an output of said comparator at the timing of the output of said delay circuit.
4. The switching circuit as set forth in claim 1 , further comprising a high pass filter circuit to which said power supply voltage is input, and a level detector which detects an output of said high pass filter circuit at a given level, said monostable multivibrator being triggered with an output of said level detector.
5. The switching circuit as set forth in claim 4 , wherein said level detector comprises a switching circuit featuring a hysteresis characteristic.
6. The switching circuit as set forth in claim 1 , wherein said delay circuit includes a second integrating circuit which integrates the output of said monostable multivibrator circuit, a level detector which detects an output of said second integrating circuit at a specific level, a differentiating circuit which differentiates an output of said level detector, and a rectifier circuit which all-wave-rectifies an output of said differentiating circuit.
7. The switching circuit as set forth in claim 1 , wherein said first integrating circuit comprises an up/down counter for counting a clock signal.