Direct conversion receiver, mobile radio equipment using the same, and RF signal receiving method
First Claim
1. A direct conversion receiver comprising:
- a frequency synthesizer for producing a local signal which is switched in frequency;
a quadrature demodulator for receiving an RF signal undergoing quadrature modulation to produce differential signals in a baseband by using said local signal from said frequency synthesizer;
a first low pass filter for conducting a band restriction on said differential signals;
a gain control amplifier for amplifying or attenuating said differential signals subjected to the band restriction;
an amplifier for amplifying output signals of said gain control amplifier;
a second low pass filter for extracting a direct current component between differential signals outputted from said amplifier;
an offset compensating unit for superimposing a feedback signal, for reducing an offset voltage between said differential signals outputted from said amplifier, on input signals to said amplifier on the basis of outputs of said second low pass filter; and
a control unit for receiving said differential signals outputted from said amplifier to output a gain control signal to said gain control amplifier for maintaining constant a level of said differential signals and for outputting data on a frequency of said local signal to be produced by said frequency synthesizer, said second low pass filter including a time constant circuit having one or more resistors and a capacitor for determining a time constant through the use of a resistance of said resistor and a capacitance of said capacitor and time constant changing means for changing the time constant of said time constant circuit to at least two values different in magnitude from each other, and said control unit including a time constant control unit for controlling said time constant changing means so that the time constant of said time constant circuit assumes the smaller one for a predetermined period of time after said control unit outputs data to change a frequency of said local signal.
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Accused Products
Abstract
In a direction conversion receiver, a quadrature demodulator produces differential signals in a baseband on the basis of a local signal of a frequency synthesizer, with the differential signals being inputted through a first low pass filter, a gain control amplifier and an amplifier to a control unit and a direct current component between the differential signals being extracted in a second low pass filter. In addition, an offset compensating section reduces an offset voltage while the control unit outputs a control signal for the control of the gain control amplifier. The second low pass filter includes a time constant circuit for determining a time constant through the use of resistors and a capacitor, and a time constant changing section. A time constant control unit controls the time constant changing section for a predetermined period of time after the control unit outputs data for the change of a frequency of the local signal so that the time constant of the time constant circuit decreases. This shortens the time needed for the settlement of automatic gain control and prevents the deterioration of demodulation accuracy during a call.
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Citations
10 Claims
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1. A direct conversion receiver comprising:
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a frequency synthesizer for producing a local signal which is switched in frequency;
a quadrature demodulator for receiving an RF signal undergoing quadrature modulation to produce differential signals in a baseband by using said local signal from said frequency synthesizer;
a first low pass filter for conducting a band restriction on said differential signals;
a gain control amplifier for amplifying or attenuating said differential signals subjected to the band restriction;
an amplifier for amplifying output signals of said gain control amplifier;
a second low pass filter for extracting a direct current component between differential signals outputted from said amplifier;
an offset compensating unit for superimposing a feedback signal, for reducing an offset voltage between said differential signals outputted from said amplifier, on input signals to said amplifier on the basis of outputs of said second low pass filter; and
a control unit for receiving said differential signals outputted from said amplifier to output a gain control signal to said gain control amplifier for maintaining constant a level of said differential signals and for outputting data on a frequency of said local signal to be produced by said frequency synthesizer, said second low pass filter including a time constant circuit having one or more resistors and a capacitor for determining a time constant through the use of a resistance of said resistor and a capacitance of said capacitor and time constant changing means for changing the time constant of said time constant circuit to at least two values different in magnitude from each other, and said control unit including a time constant control unit for controlling said time constant changing means so that the time constant of said time constant circuit assumes the smaller one for a predetermined period of time after said control unit outputs data to change a frequency of said local signal. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A mobile radio equipment comprising a direct conversion receiver including:
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a frequency synthesizer for producing a local signal which is switched in frequency;
a quadrature demodulator for receiving an RF signal undergoing quadrature modulation to produce differential signals in a baseband by using said local signal from said frequency synthesizer;
a first low pass filter for conducting a band restriction on said differential signals;
a gain control amplifier for amplifying or attenuating said differential signals subjected to the band restriction;
an amplifier for amplifying output signals of said gain control amplifier;
a second low pass filter for extracting a direct current component between differential signals outputted from said amplifier;
an offset compensating unit for superimposing a feedback signal, for reducing an offset voltage between said differential signals outputted from said amplifier, on input signals to said amplifier on the basis of outputs of said second low pass filter; and
a control unit for receiving said differential signals outputted from said amplifier to output a gain control signal to said gain control amplifier for maintaining constant a level of said differential signals and for outputting data on a frequency of said local signal to be produced by said frequency synthesizer, said second low pass filter having a time constant circuit having one or more resistors and a capacitor for determining a time constant through the use of a resistance of said resistor and a capacitance of said capacitor and time constant changing means for changing the time constant of said time constant circuit to at least two values different in magnitude from each other, and said control unit having a time constant control unit for controlling said time constant changing means so that the time constant of said time constant circuit assumes the smaller one for a predetermined period of time after said control unit outputs data to change a frequency of said local signal.
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8. A method of receiving an RF signal, comprising:
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a step of producing a local signal which is switched in frequency;
a step of receiving an RF signal undergoing quadrature modulation to produce differential signals in a baseband by using said local signal;
a step of conducting a band restriction on said differential signals;
a step of amplifying or attenuating said differential signals subjected to the band restriction;
a step of amplifying said differential signals amplified or attenuated;
a step of extracting a direct current component between the amplified differential signals;
a step of reducing an offset voltage between said differential signals on the basis of the extracted direct current component; and
a step of maintaining constant a level of the amplified differential signals and of outputting data on a frequency of said local signal, said direct current component extracting step including;
a step of determining a time constant through the use of a resistance of one or more resistors and a capacitance of a capacitor and of changing the time constant to at least two values different in magnitude from each other; and
a step of controlling the time constant to the smaller one for a predetermined period of time after an instruction for a change of the frequency of said local signal.
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9. A direct conversion receiver comprising:
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a frequency synthesizer for producing a local signal which is switched in frequency;
a quadrature demodulator for receiving an RF signal undergoing quadrature modulation to produce differential signals in a baseband by using said local signal from said frequency synthesizer;
a first low pass filter for conducting a band restriction on said differential signals;
a gain control amplifier for amplifying or attenuating said differential signals subjected to the band restriction;
an amplifier for amplifying output signals of said gain control amplifier;
a second low pass filter for extracting a direct current component between differential signals outputted from said amplifier, said second low pass filter including a time constant circuit having one or more resistors and a capacitor for determining a time constant through the use of a resistance of said resistor and a capacitance of said capacitor and time constant changing means for changing the time constant of said time constant circuit to at least two values different in magnitude from each other;
an offset compensating unit for superimposing a feedback signal, for reducing an offset voltage between said differential signals outputted from said amplifier, on input signals to said amplifier on the basis of outputs of said second low pass filter;
a control unit for receiving said differential signals outputted from said amplifier to output a gain control signal to said gain control amplifier for maintaining constant a level of said differential signals and for outputting data on a frequency of said local signal to be produced by said frequency synthesizer; and
a time constant control unit for receiving said gain control signal from said control unit to control the time constant of said time constant circuit of said second low pass filter by means of said time constant changing means through the use of said gain control signal therefrom. - View Dependent Claims (10)
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Specification