KR100267847B1 - Apparatus and method for converting frequency - Google Patents

Abstract

PURPOSE: A frequency converting device is provided to combine a reverse phase signal, which has an identical size with a local oscillating frequency, with an output terminal of a mixer in order to remove a leakage of the local oscillating frequency. CONSTITUTION: A local oscillator(11) generates a local oscillating frequency. A mixer(12) mixes an inputted signal with the local oscillating frequency for outputting. A level converter(42) converts a level of the local oscillating frequency into a level of a leakage local oscillating frequency. A phase modulator(43) performs a reverse phase conversion for an output of the level converter(42). A combiner(44) combines an output of the mixer(12) with an output of the phase converter(43), and removes the local oscillating frequency included in the output of the mixer(12).

Description

Frequency converter and method {APPARATUS AND METHOD FOR CONVERTING FREQUENCY}

The present invention relates to a frequency converter and a method of a wireless communication system, and more particularly to a device and method that can remove the leakage signal of the local oscillation frequency in the frequency converter.

In general, the frequency converter refers to a device for converting a frequency transmitted and received in a wireless communication device. At this time, the frequency converter of the transmitter is an up-converter, and a carrier wave is mixed with the baseband signal to up-convert the frequency of the transmission signal, and the frequency converter of the receiver is a downconverter. As a down-converter, the carrier is removed from the received RF signal and down-converted to the original signal.

The frequency converter includes a mixer, and the mixer performs a function of increasing or decreasing a frequency by mixing a transmission or reception signal with a local oscillation frequency. In the embodiment of the present invention, a rise converter will be described as an example.

1 and 4 illustrate a conventional configuration in which a local oscillation frequency and a signal are mixed in a device for up-converting a frequency, and a local oscillator 11 is a local oscillation frequency for converting a frequency. LF). The mixer 12 mixes and outputs an IF signal (Iermediate Frequency) and the local oscillation frequency. 2 is a diagram illustrating a frequency spectrum output from the mixer 12, in which the local oscillation frequency leaking in the frequency spectrum is represented at the highest level. In this case, the IF signal is a signal generated through a first-order frequency conversion process at the front end. The band filter 13 filters the frequency band up-converted at the output of the mixer 12. The amplifier 14 amplifies the up-converted signal output from the bandpass filter 13 and outputs the RF signal as a radio frequency (RF). FIG. 1 illustrates a configuration in which a notch filter 15 is connected to the output terminal of the mixer 12 to lower the level of the local oscillation frequency leaked from the mixer 12.

Referring to the frequency conversion operation of FIG. 1, the mixer 12 mixes and outputs an input IF signal and a local oscillation frequency. At this time, if the IF signal is called Fif, the local oscillation frequency is called Flo, and the output of mixer 12 is Fo, the Fo can be expressed as Equation 1 below.

Where n, m = 0,1,2,3, ... In FIG. 1, a nutch filter 15 is used to remove the local oscillation frequency Flo at the output of the mixer 12, and the characteristics of the notch filter 15 are designed as shown in FIG. The characteristics of the notch filter 15 are as shown in Equation 2 below.

Therefore, the nutch filter 15 generates resonance at the same point as in Equation 2, and removes the leaked local oscillation frequency by using this characteristic.

In addition, the frequency converter having the configuration as shown in FIG. 4 removes the local oscillation signal Flo leaked using the bandpass filter 21. At this time, the pass band of the band filter 21 is designed as a local oscillation frequency band. Therefore, the band oscillator 23 removes the local oscillation frequency gained by the amplifier 22 from the final output signal. Therefore, the frequency converter as shown in FIG. 4 uses a bandpass filter 21 to remove the local oscillation frequency Flo included in the output Fo of the mixer 12, and passes the local oscillation signal having a gain by the amplifier 22 through the bandpass filter 23 again. It's a way to remove it.

However, in the case of removing the leaked local oscillation frequency Flo with the configuration as shown in FIG. 1, when configuring the nutch filter 15, the deviation of the inductor and capacitor values occurs according to the frequency so that the local oscillation frequency is a desired signal. It is difficult to attenuate to the size of, and the higher the frequency, the greater the variation in component values and the difficulty in implementation. Therefore, there is a problem in that it is difficult to remove the local oscillation frequency, which is a desired signal, to a desired level due to component variation.

In addition, when the local oscillation frequency Flo leaked in the configuration as shown in FIG. 4 is removed, as shown in the frequency spectrum of the mixer 12 as shown in FIG. In order to satisfy the spectrum mask, multiple band filters 21 and 23 should be used. This increases the price of the product to implement the bandpass filter, there is a disadvantage in the price of the product by inserting additional parts.

However, current wireless communication systems are increasingly adopting a method of directly converting a baseband signal into an RF signal. In this case, since the leakage of the local oscillation frequency is less than the product specification related to the transmission frequency spectrum, a lot of time and effort is invested to further remove the local oscillation frequency. Therefore, the frequency converter of the wireless communication system should be designed to efficiently remove the local oscillation frequency and easily satisfy the output spectrum specification of the transmitter. In particular, when designing a frequency converter using the direct conversion method, it is impossible to remove the local oscillation frequency in the configuration as shown in FIG.

Accordingly, an object of the present invention is to provide an apparatus and method for removing a local oscillation frequency leaking from a mixer by combining an antiphase signal having the same magnitude as that of a local oscillation frequency in a frequency converter.

It is still another object of the present invention to provide an apparatus and a method for removing local oscillation frequency leaking from a mixer of a frequency converter using a direct conversion method.

According to an aspect of the present invention, there is provided a frequency converting apparatus comprising: a local oscillator for generating a local oscillation frequency, a mixer for mixing and outputting an input signal and the local oscillation frequency, and coupling the level of the local oscillation frequency; A level oscillator for converting the leaked local oscillation frequency to a level, a phase modulator for converting the output of the level converter to an inverse phase, and an output of the mixer and an output of the phase modulator to combine local oscillation included in the mixer output. It is characterized by consisting of a combiner to remove the frequency.

1 is a diagram showing a configuration of mixing a signal and a local oscillation frequency in a conventional frequency converter;

2 is a diagram showing a frequency spectrum generated in a frequency converter;

FIG. 3 is a diagram illustrating the characteristics of the notch filter in FIG. 1. FIG.

4 is a view showing another configuration of mixing a signal and a local oscillation frequency in a conventional frequency converter;

5 is a diagram illustrating a configuration in which a signal and a local oscillation frequency are mixed in a frequency conversion device according to an embodiment of the present invention.

Fig. 6 shows the spectrum of the harmonic frequency of the mixer.

7 shows an antiphase frequency spectrum.

8 is a diagram illustrating a characteristic in which a local oscillation frequency is removed in a time domain;

9 is a diagram showing an example in which an embodiment of the present invention is applied to a frequency converter using a direct conversion method.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

5 is a diagram illustrating a configuration for removing leakage of a local oscillation frequency in a frequency converter according to an embodiment of the present invention.

Referring to the configuration of FIG. 5, the local oscillator 11 generates a local oscillation frequency for converting the frequency. The mixer 12 mixes and outputs an IF signal and the local oscillation frequency.

The divider 41 divides the power of the local oscillation frequency output from the local oscillator 11 and outputs the power to the mixer 12 and the level converter 41. The level converter 42 adjusts the level of the local oscillation frequency inputted by power distribution to the magnitude of the leakage signal output from the mixer 12. A phase modulator 43 modulates the phase of the local oscillation frequency output from the level converter 42 in reverse phase and outputs it. The combiner 44 combines the mixed signal output from the mixer 12 and the local oscillation frequency of the inverse phase output from the phase modulator 43 to remove the local oscillation frequency leaked to the mixed signal.

The band filter 45 filters the frequency band up-converted from the mixed signal from which the local oscillation frequency is removed from the combiner 44. The amplifier 46 amplifies the up-converted signal output from the bandpass filter 45 and outputs the RF signal.

FIG. 2 illustrates a frequency spectrum of the mixed signal output from the mixer 12, and the spectrum of the local oscillation frequency is the highest level among the frequency spectrums. FIG. 6 illustrates a harmonic frequency spectrum output from the mixer 12, and it can be seen that the spectrum of the local oscillation frequency is the highest among the output mixed signals. FIG. 7 illustrates a reverse phase local oscillation frequency spectrum output by the phase modulator 43 to remove the local oscillation frequency from the harmonic frequency spectrum of the mixer 12 as shown in FIG. 8 is a waveform diagram illustrating a characteristic of removing a local oscillation signal in a time domain, in which 8a represents the magnitude of the leaked local oscillation frequency included in the output of the mixer 12, and 8b represents an inverse of the output of the phase modulator 43. The magnitude of the local oscillation frequency of the phase is shown, and 8c shows a state in which the local oscillation frequency leaking from the combiner 44 is removed.

In the frequency converter according to the embodiment of the present invention, as shown in FIG. 5, after the power is distributed to a part of the local oscillation frequency output from the local oscillator 11, the divided local oscillation frequency is leaked to the level of the local oscillation signal leaking. By converting the phase shifted local oscillation frequency to reverse phase and combining it with the output of the mixer 12, the local oscillation frequency included in the output of the mixer 12 is removed.

The frequency spectrum output from the mixer 12 is generated as shown in FIG. 2. As shown in FIG. 2, the signal level of the local oscillation frequency Flo is very large on the output frequency spectrum of the mixer, and the Flo must be removed to satisfy the output spectrum required by the system. In addition, the harmonic frequency output from the mixer 12 is generated as shown in FIG. 6, in which case it becomes difficult to remove the second and third harmonic frequencies. That is, as shown in FIG. 6, the harmonic frequency Flo × 2 of Flo is generated, and Frf_low and Ffr_high are generated according to the harmonic frequency. Therefore, as shown in FIG. 6, the output of the mixer 12 is generated as in Equation 3 below. At this time, the level of Flo included in the output of the mixer 12, that is, the magnitude Floi of the leakage signal of the local oscillator 11 is expressed by Equation 3 below.

Floi = Local Oscillator Level (dBm)-Input Signal Level (dBm) + SSB Conversion Loss (dB) + Mix Loss (dBc)

In Equation 3, the input signal is an RF signal in the case of a transmitter and an IF signal in the case of a receiver.

변환하여 상기 혼합기12에서 출력되는 혼합신호에 포함된 국부발진주파수와 역위상이 되도록 변조한다. 이때 상기 위상변조기43에서 출력되는 국부발진주파수의 위상은 도 8의 8b와 같이 상기 누설신호와 역위상으로 발생한다. 따라서 상기 결합기44에서는 상기 혼합신호와 상기 위상변조기43의 출력을 결합하여 국부발진주파수를 제거하며, 이로인해 상기 대역여파기13에 인가되는 신호에서 국부발진주파수의 크기는 도 8의 8c와 같이 제거됨을 알 수 있다.In FIG. 5, the divider 41 distributes the signal power of the local oscillation frequency output to the local oscillator 11 and applies it to the level converter 42. The level converter 42 then converts the level such that the distributed local oscillation frequency has the same magnitude as that of the local oscillation frequency included in the mixed signal output from the mixer 12. That is, when the magnitude of the leakage signal of the local oscillation frequency included in the mixed signal is the same as 8a of FIG. The phase modulator 43 shifts the phase of the level-converted local oscillation frequency by 180.

It converts and modulates to be out of phase with the local oscillation frequency included in the mixed signal output from the mixer 12. At this time, the phase of the local oscillation frequency output from the phase modulator 43 is generated out of phase with the leakage signal as shown in 8b of FIG. Therefore, in the combiner 44, the local oscillation frequency is removed by combining the mixed signal and the output of the phase modulator 43, whereby the magnitude of the local oscillation frequency is removed from the signal applied to the band filter 13 as shown in 8c of FIG. Able to know.

That is, when the mixer 12 outputs the mixed signal as shown in FIG. 6, the level converter 42 adjusts the level of the local oscillation frequency to have the same size as that of the level of the Flo and the secondary flo, and a phase modulator. 43 modulates the level-converted local oscillation frequency into an inverse phase as shown in FIG. Then, the combiner 44 removes the local oscillation frequency included in the signal output from the mixer 12 and applies it to the bandpass filter 45.

쉬프트되어 혼합기94에 인가된다. 그러면 상기 혼합기92 및 94는 각각 I 및 Q 입력신호와 상기 국부발진주파수를 혼합하며, 결합기91은 상기 혼합기92 및 94의 혼합신호를 가산하여 RF 또는 IF신호를 출력한다. 이때 상기 국부발진주파수는 변환기95에 인가되며, 상기 변환기95는 상기 국부발진신호의 레벨을 레벨을 혼합신호에 포함되는 누설된 국부발진주파수의 레벨로 변환하고, 변환된 국부발진주파수의 위상을 역위상으로 변환한 후, 결합기96에 인가한다.9 shows an embodiment in which the local oscillation frequency cancellation circuit according to the embodiment of the present invention is applied to a frequency conversion device using a direct conversion method. In this configuration, the converter 95 includes the level converter 42 and the phase modulator 43. 9 shows an example of a transmitter. Referring to FIG. 9, the local oscillation frequency generated by the local oscillator 90 is applied to the mixer 92, and the phase shifter 93 to 90.

It is shifted and applied to mixer 94. The mixers 92 and 94 then mix the I and Q input signals and the local oscillation frequency, respectively, and the combiner 91 adds the mixed signals of the mixers 92 and 94 to output an RF or IF signal. In this case, the local oscillation frequency is applied to the converter 95, and the converter 95 converts the level of the local oscillation signal into the level of the leaked local oscillation frequency included in the mixed signal, and reverses the phase of the converted local oscillation frequency. After conversion to phase, it is applied to combiner 96.

Therefore, in the frequency conversion device using the direct conversion method, the local oscillation frequency output from the local oscillator 90 is adjusted to the level of the leaking local oscillation frequency, converted to be in phase with the leaking local oscillation frequency, and applied to the combiner 96. Therefore, the combiner 96 can remove the local oscillation frequency included in the mixed signal.

As described above, in order to remove the local oscillation frequency leaked from the mixer, the level of the local oscillation frequency output from the local oscillator is adjusted and converted to the reverse phase to combine the mixed signal to remove the local oscillation frequency included in the output signal. Therefore, it is possible to remove the local oscillation frequency leaked from the mixer with a simple configuration, and it is possible to efficiently remove the local oscillation signal that is difficult to solve in the frequency converter using the direct conversion method.

Claims (4)

In the frequency conversion device of a wireless communication system, A local oscillator for generating a local oscillation frequency, A mixer for mixing and outputting an input signal and the local oscillation frequency; A level converter for converting the level of the local oscillation frequency into the level of the leaked local oscillation frequency; A phase modulator for converting the output of the level converter into an inverse phase; And a combiner for coupling the output of the phase modulator to the output of the mixer to remove local oscillation frequencies included in the mixer output. The frequency converter of claim 1, further comprising a band filter connected to the combiner and configured to filter a low frequency band from an output signal of the mixer to upconvert the input signal. 2. The frequency converter of claim 1, further comprising a band filter connected to the combiner and filtering a low frequency band to the output signal of the mixer to down convert the input signal. In the frequency conversion method of a wireless communication system, Generating a local oscillation frequency, Mixing the input signal with the local oscillation frequency; Converting the level of the local oscillation frequency into the level of the leaked local oscillation frequency; Converting the output of the level converter to an inverse phase; And combining the mixed signal and the local oscillation frequency of the inverse phase to remove the local oscillation frequency included in the output of the mixer.

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