Downconverter and upconverter
A downconverter and upconverter are provided which can obtain a sufficient image rejection ratio in a low-Intermediate Frequency (IF) scheme while reducing power consumption and can suppress Error Vector Magnitude (EVM)-related degradation in a zero-IF scheme. A complex-coefficient transversal filter rejects one side of a positive or negative frequency, and converts a Radio Frequency (RF) signal to a complex RF signal configured by real and imaginary parts. A local oscillator outputs a real local signal with a set frequency. A half-complex mixer, connected to the complex-coefficient transversal filter and the local oscillator, performs a frequency conversion process by multiplying the complex RF signal output from the complex-coefficient transversal filter and the real local signal output from the local oscillator, and outputs a complex signal of a frequency separated by the set frequency from a frequency of the RF signal.
1. A downconverter for downconverting a Radio Frequency (RF) signal, comprising:
a complex-coefficient transversal filter for generating a real part of a complex RF signal by performing a convolution integral according to a generated impulse response based on an even function for an input RF signal, generating an imaginary part of the complex RF signal by performing a convolution integral according to a generated impulse response based on an odd function for the input RF signal, rejecting one side of a positive or negative frequency, and outputting the complex RF signal;
a local oscillator for outputting a real local signal at a set frequency; and
a complex mixer, connected to the complex-coefficient transversal filter and the local oscillator, for performing a frequency conversion process by multiplying the complex RF signal output from the complex-coefficient transversal filter and the real local signal output from the local oscillator, and outputting a complex signal of a frequency separated by the set frequency from a frequency of the RF signal.
2. The downconverter of claim 1 , wherein the complex-coefficient transversal filter is configured by a Surface Acoustic Wave (SAW) filter.
3. The downconverter of claim 1 , wherein the set frequency has a frequency value out of a channel signal band of the RF signal.
4. The downconverter of claim 3 , further comprising:
a second complex-coefficient transversal filter, connected to the complex mixer, for rejecting a positive or negative frequency of the complex signal output from the complex mixer and outputting a rejection result.
5. The downconverter of claim 4 , wherein the second complex-coefficient transversal filter is configured by a SAW filter.
6. The downconverter of claim 5 , further comprising:
means for receiving the complex signal output from the complex mixer, inverting a sign of an imaginary axis signal of the complex signal, and generating a complex conjugate signal corresponding to a complex conjugate of the complex signal;
means for adjusting a level of the complex conjugate signal; and
means for combining the complex signal output from the complex mixer and the complex conjugate signal whose level is adjusted.
7. The downconverter of claim 4 , wherein the frequency separated by the set frequency from the RF signal is set to a frequency of more than a half value of a difference between a frequency of a pass band end of the complex-coefficient transversal filter and the RF signal frequency.
8. The downconverter of claim 5 , wherein the frequency separated by the predetermined frequency from the RF signal is set to a frequency of more than a half value of a difference between a frequency of a pass band end of the complex-coefficient transversal filter and the RF signal frequency.
9. The downconverter of claim 6 , wherein the frequency separated by the set frequency from the RF signal is set to a frequency of more than a half value of a difference between a frequency of a pass band end of the complex-coefficient transversal filter and the RF signal frequency.
10. A downconverter for downconverting a Radio Frequency (RF) signal, comprising:
a distributor, provided with a plurality of output terminals, for switching and outputting an input RF signal;
a plurality of complex-coefficient transversal filters having different band pass frequencies in a plurality of transversal filters connected to the plurality of output terminals of the distributor in a one-to-one correspondence, the plurality of complex-coefficient transversal filters outputting a real part of a complex RF signal by performing a convolution integral according to a generated impulse response based on an even function for the RF signal output from the distributor, outputting an imaginary part of the complex RF signal by performing a convolution integral according to a generated impulse response based on an odd function for the RF signal output from the distributor, rejecting one side of a positive or negative frequency in the band pass frequencies, and outputting the complex RF signal;
a local oscillator for switching and outputting a real local signal of a frequency according to the band pass frequencies of the plurality of complex-coefficient transversal filters;
a plurality of complex mixers connected to the plurality of complex-coefficient transversal filters in the one-to-one correspondence and connected to the local oscillator, the plurality of complex mixers performing a frequency conversion process by multiplying the complex signal output from the complex-coefficient transversal filter and the real local signal output from the local oscillator, and outputting a complex signal of a frequency separated by a set frequency from a frequency of the RF signal; and
a combiner, connected to the plurality of complex mixers, for switching a connection of the plurality of complex mixers and outputting the complex signal outputted from the plurality of complex mixers.