Voltage hold circuit and clock synchronization circuit
First Claim
Patent Images
1. A voltage hold circuit which holds a voltage of an external input signal, comprising:
- a voltage comparator unit configured to output a result of comparison between a voltage of an externally inputted control signal and a voltage of an analog hold signal outputted from the voltage hold circuit;
a digital value hold unit configured to increase or decrease a hold value which is a digital value held by the digital value hold unit, based on the comparison result, to output a digital hold signal which is a digital value generated based on the hold value, and configured to maintain said hold value notwithstanding said comparison result in response to a signal indicating unreliability of said control signal; and
a D/A converter unit configured to convert the digital hold signal to an analog value for output as the analog hold signal.
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Abstract
A voltage hold circuit which holds an input signal voltage includes a voltage comparator unit configured to output a result of comparison between a voltage of an externally inputted control signal and a voltage of an outputted analog hold signal, a digital value hold unit configured to increase or decrease a hold value which is a digital value it holds, based on the comparison result, and to output a digital hold signal which is a digital value generated based on the hold value, and a D/A converter unit configured to convert the digital hold signal to an analog value for output as the analog hold signal.
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Citations
8 Claims
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1. A voltage hold circuit which holds a voltage of an external input signal, comprising:
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a voltage comparator unit configured to output a result of comparison between a voltage of an externally inputted control signal and a voltage of an analog hold signal outputted from the voltage hold circuit; a digital value hold unit configured to increase or decrease a hold value which is a digital value held by the digital value hold unit, based on the comparison result, to output a digital hold signal which is a digital value generated based on the hold value, and configured to maintain said hold value notwithstanding said comparison result in response to a signal indicating unreliability of said control signal; and a D/A converter unit configured to convert the digital hold signal to an analog value for output as the analog hold signal. - View Dependent Claims (2, 3, 4, 5)
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6. A clock synchronization circuit, comprising:
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an oscillator configured to control a frequency of an output clock signal to be outputted, based on a voltage of an input control signal; a phase comparator configured to output a phase difference between an externally inputted reference clock signal and a comparison clock signal based on the output clock signal, which phase difference output is used to develop said input control signal; a voltage hold circuit configured to hold a voltage corresponding to the control signal; and a switch configured to receive the control signal and an analog hold signal outputted from the voltage hold circuit, and to input the analog hold signal to the oscillator when obtaining an alarm signal showing that a reliable reference clock signal is not inputted, and to input the control signal to the oscillator when not obtaining the alarm signal; the voltage hold circuit comprising; a voltage comparator unit configured to output a result of comparison between the voltage of the control signal and a voltage of the analog hold signal; a digital value hold unit configured to increase or decrease a hold value which is a digital value held by the digital value hold unit, based on the comparison result, and to output a digital hold signal which is a digital value generated based on the hold value; and a D/A converter unit configured to convert the digital hold signal to an analog value for output as the analog hold signal.
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7. A voltage hold circuit which holds a voltage of an external input signal, comprising:
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a voltage comparator unit configured to output a result of comparison between a voltage of an externally inputted control signal and a voltage of an analog hold signal outputted from the voltage hold circuit; a digital value hold unit configured to increase or decrease a hold value which is a digital value held by the digital value hold unit, based on the comparison result, and to output a digital hold signal which is a digital value generated based on the hold value; and a D/A converter unit configured to convert the digital hold signal to an analog value for output as the analog hold signal, and wherein the digital value hold unit is configured to output an average value of hold values in a certain past period as the digital hold signal. - View Dependent Claims (8)
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Specification