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US 5,335,270 AGranted
Bell signal generating circuit
AssigneeKabushiki Kaisha Toshiba
InventorsMasayuki Tsurusaki, Takashi Watanabe
Life of this patent
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Abstract
A bell signal generating circuit for a key telephone set. A dc component of a pulse signal is removed by a photo-coupler to generate a first signal. A high frequency component of the first signal is removed by a filter to generate a second signal. A differential amplifier amplifies the second signal to generate a bell signal. To the differential amplifier, a dc supply voltage based on the dc signal in synchronism when the pulse signal is applied.
Claims3
A bell signal generating circuit, comprising:
- means for generating a pulse signal and a direct current signal in synchronism with the pulse signal;
- a photo-coupler for removing a direct current component of the pulse signal to output a first signal;
- a filter connected to the photo-coupler, for removing higher harmonics of the first signal to output a second signal;
- a differential amplifier connected to the filter, for differentially amplifying the second signal to output a bell signal;
- and
- means, responsive to the direct current signal, for applying a direct current supply voltage to the differential amplifier.
3 more elements
A method of generating a bell signal for a key telephone set, comprising the steps of:
- generating a pulse signal and a direct current signal in synchronism with the pulse signal;
- removing a direct current component of the pulse signal to output a first signal;
- removing higher harmonics of the first signal to output a second signal;
- differentially amplifying the second signal to output a bell signal by a differential amplifier;
- and
- applying a direct current supply voltage to the differential amplifier in response to the direct current signal.
3 more elements
Dependencies are inferred from the claim text.