Radio receiving apparatus for receiving communication signals of different bandwidths
First Claim
1. A radio receiving apparatus for a radio system in which carrier frequencies are channel-positioned at equal frequency intervals or positioned in a manner similar thereto and which employs a quadrature demodulation scheme or a demodulation scheme similar thereto, said radio receiving apparatus comprising:
- means supplied with a received signal including a signal of a reception-desired channel, for selectively converting, into an intermediate frequency band or a DC-inclusive band, a frequency band including up to approximately 12 channels on each of upper and lower sides of a center frequency that is an upper or lower end of the reception-desired channel or a boundary frequency with an adjacent channel thereof;
means for sampling the frequency-converted signal at a frequency that is 64-fold a bandwidth of the reception-desired channel or 64-fold of a 1/2 frequency of a channel interval frequency of the radio system;
means for extracting orthogonal components in a phase domain from the sampled signal;
means for extracting a signal of four channels including the reception-desired channel from a real-axis signal component and an imaginary-axis signal component of the extracted orthogonal components while rejecting a signal of the other adjacent channels; and
means for extracting only the signal of the reception-desired channel while rejecting a signal of the other adjacent channels with a sampling frequency set at a frequency that is 16-fold the bandwidth of the reception-desired channel or 16-fold of the 1/2 frequency of the channel interval frequency of the radio system.
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Abstract
A received signal obtained from an antenna is subjected to high-frequency amplification. The amplified signal is supplied to a first bandpass filter, which extracts only signals of all the channels of a communications system concerned while filtering out other radio signals. The extracted signals are frequency-converted by using a local oscillation frequency, and only a desired wave is passed by a second bandpass filter. The desired wave is supplied to a sample-and-hold circuit, which performs sampling according to the bandwidth-limiting sampling theorem. A resulting discrete signal is supplied to an I-axis-component and Q-axis-component separating circuits, where the polarity of sample values is inverted for every other clock pulse with respect to each of the I and Q axes to thereby effect Hilbert transform. Resulting two orthogonal components on a phase plane are supplied to a complex coefficient filter.
35 Citations
9 Claims
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1. A radio receiving apparatus for a radio system in which carrier frequencies are channel-positioned at equal frequency intervals or positioned in a manner similar thereto and which employs a quadrature demodulation scheme or a demodulation scheme similar thereto, said radio receiving apparatus comprising:
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means supplied with a received signal including a signal of a reception-desired channel, for selectively converting, into an intermediate frequency band or a DC-inclusive band, a frequency band including up to approximately 12 channels on each of upper and lower sides of a center frequency that is an upper or lower end of the reception-desired channel or a boundary frequency with an adjacent channel thereof; means for sampling the frequency-converted signal at a frequency that is 64-fold a bandwidth of the reception-desired channel or 64-fold of a 1/2 frequency of a channel interval frequency of the radio system; means for extracting orthogonal components in a phase domain from the sampled signal; means for extracting a signal of four channels including the reception-desired channel from a real-axis signal component and an imaginary-axis signal component of the extracted orthogonal components while rejecting a signal of the other adjacent channels; and means for extracting only the signal of the reception-desired channel while rejecting a signal of the other adjacent channels with a sampling frequency set at a frequency that is 16-fold the bandwidth of the reception-desired channel or 16-fold of the 1/2 frequency of the channel interval frequency of the radio system.
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2. The radio receiving apparatus according to claim 1, comprising:
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a sample-and-hold circuit for sampling the frequency-converted signal at the frequency that is 64-fold the bandwidth of the reception-desired channel or 64-fold of the 1/2 frequency of the channel interval frequency of the radio system; a Hilbert transformer for extracting the orthogonal components in the phase domain from a sampled output of the sample-and-hold circuit, and for generating the real-axis signal component and the imaginary-axis signal component; a first complex coefficient filter for rejecting a signal of channels other than three adjacent channels on each of the upper and lower sides of the desired channel from the real-axis signal component and the imaginary-axis signal component; two first phase equalizers for receiving respective outputs of the first complex coefficient filter; two first lowpass filters for receiving respective outputs of the two first phase equalizers; a first decimation circuit for decimating outputs of the two first lowpass filters into 1/4; a second complex coefficient filter for rejecting a signal of the three adjacent channels on each of the upper and lower sides of the desired channel from the real-axis signal component and the imaginary-axis signal component that are outputted from the first decimation circuit, and for converting the signal of the desired channel into a baseband signal; two second phase equalizers for receiving respective outputs of the second complex coefficient filter; two second lowpass filters for receiving respective outputs of the two second phase equalizers; a second decimation circuit for decimating outputs of the two second lowpass filters into 1/4; and an image-rejecting frequency conversion circuit for eliminating an offset frequency from two outputs of the second decimation circuit.
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3. The radio receiving apparatus according to claim 1, comprising:
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a sample-and-hold circuit for sampling the frequency-converted signal at the frequency that is 64-fold the bandwidth of the reception-desired channel or 64-fold the 1/2 frequency of the channel interval frequency of the radio system; a Hilbert transformer for extracting orthogonal components in the phase domain from a sampled output of the sample-and-hold circuit, and for generating the real-axis signal component and the imaginary-axis signal component; a first complex coefficient filter for rejecting a signal of channels other than three adjacent channels on each of the upper and lower sides of the desired channel from the real-axis signal component and the imaginary-axis signal component; two first phase equalizers for receiving respective outputs of the first complex coefficient filter; a first averaging circuit for averaging outputs of the two first phase equalizers over eight samples; a second complex coefficient filter for rejecting a signal of the three adjacent channels on each of the upper and lower sides of the desired channel from the real-axis signal component and the imaginary-axis signal component that are outputted from the first averaging circuit, and for converting the signal of the desired channel into a baseband signal; two second phase equalizers for receiving respective outputs of the second complex coefficient filter; a second averaging circuit for averaging outputs of the two second phase equalizers over eight samples; and an image-rejecting frequency conversion circuit for eliminating an offset frequency from two outputs of the second averaging circuit.
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4. The radio receiving apparatus according to claim 2, wherein the Hilbert transformer includes a buffer amplifier and an inverted amplifier, each being a switched-capacitor circuit, and a switch.
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5. The radio receiving apparatus according to claim 2, wherein the complex coefficient filters have only two kinds of values as absolute values of coefficients.
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6. The radio receiving apparatus according to claim 2, wherein operational amplifiers of the two first phase equalizers are respectively used in common with those of the two first lowpass filters ensuing the two first phase equalizers, and wherein operational amplifiers of the two second phase equalizers are respectively used in common with those of the two second lowpass filters ensuing the two second phase equalizers.
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7. The radio receiving apparatus according to claim 6, wherein the two first lowpass filters and the two second lowpass filters are constituted by using a CCD, to reduce the number of operational amplifiers.
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8. The radio receiving apparatus according to claim 3, wherein the Hilbert transformer includes a buffer amplifier and an inverted amplifier, each being a switched-capacitor circuit, and a switch.
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9. The radio receiving apparatus according to claim 3, wherein the complex coefficient filters have only two kinds of values as absolute values of coefficients.
Specification