KR20100059178A - Apparatus and method for converting digital signal to radio frequency signal directly - Google Patents

Abstract

PURPOSE: An apparatus and a method for directly changing a digital signal into a radio frequency signal are provided to embody DAC, an image filter, and a mixer in one chip. CONSTITUTION: A DAC(Digital-Analog Converter)(320) changes a different phase digital signal into an analog signal. An image filter(330) removes a frequency band in which generation of an image signal is expected in the mixing of an oscillation frequency and an analog signal. A mixer(340) changes the signal from which the frequency band is removed into a radio frequency band. The DAC, image filter and mixer are integrated in one chip. The image-removed filter comprises a switch for controlling the removed frequency band.

Description

Apparatus and method for directly converting digital signals into radio frequency signals {APPARATUS AND METHOD FOR CONVERTING DIGITAL SIGNAL TO RADIO FREQUENCY SIGNAL DIRECTLY}

The present invention relates to a transmission apparatus for directly converting a digital signal into a radio frequency signal and a transmission method thereof. More specifically, in order to remove the image signal generated in the frequency up-conversion process in advance, after converting the digital base band or intermediate frequency signal into an analog signal, the frequency band expected to generate the image signal in advance to remove the frequency up A transmission apparatus and method for converting the same.

Modern wireless communication systems have a need for a radio frequency (RF) transmitter with improved efficiency while preventing distortion. The conventional RF transmitter for this purpose converts a digital baseband or intermediate frequency signal having a meaning into an analog signal, and passes through an analog low pass filter (LPF) to convert it into an RF signal using a mixer.

Such conventional RF transmitters require a converter for converting a digital signal into an analog signal. There is also a need for an I / Q modulator to separate the baseband digital signal into inphase and quadrature. Such D / A converters and I / Q modulators are not only complex but also high performance analog elements, which can limit the flexibility of the RF transmitter. In particular, in the case of multimode multiband RF, this limited flexibility may impose many restrictions on the wireless communication environment.

In order to solve the above problems, a direct conversion method for simultaneously converting a digital signal into an analog signal and mixing for frequency up-conversion has been proposed. However, in the conventional direct conversion method, an image removal filter for removing an image signal generated in a frequency up-conversion process is located at the end. In this case, the image rejection filter needs to filter at a high frequency RF frequency and thus requires a higher level of sharpness (Q-factor). However, there is a problem that it is not easy to design a filter having such a high level of sharpness.

The present invention has been made to solve the above problems, in order to remove the image signal generated during the frequency up-conversion process in advance to convert the digital baseband or intermediate frequency signal after the analog signal conversion frequency is expected to generate the image signal It is to upconvert the frequency after removing the band in advance.

Another object of the present invention is to reduce the size and the production cost by implementing a digital analog converter, an image cancellation filter and a mixer in one chip.

In order to solve the above problems, a transmission apparatus for directly converting a digital signal of the present invention into a radio frequency signal includes a digital analog converter for receiving a digital signal having a different phase and converting it into an analog signal, and the converted analog signal and the oscillation frequency. An image removal filter for removing in advance a frequency band in which an image signal is expected to be generated, and a mixer configured to frequency-upconvert a signal from which the image signal generation band in advance is removed to a radio frequency band, wherein the digital analog converter and the The image rejection filter and the mixer are integrated on one chip.

In addition, a transmission method for directly converting a digital signal to a radio frequency signal to solve the above problems is to receive a digital signal having a different phase and convert it into an analog signal, the image when mixing the converted analog signal and the oscillation frequency And removing the frequency band in which the generation of the signal is expected in advance and frequency-up converting the signal from which the image signal generation expected band is removed in advance to the radio frequency band.

According to the transmission device and the transmission method of the present invention, a digital analog converter, an image removal filter, and a mixer can be implemented on one chip by removing a digital baseband or an intermediate frequency signal in advance after the analog signal conversion. There is an advantage. This can reduce chip size and reduce production costs. In addition, by performing the filtering before the frequency up-conversion, an image rejection filter having the same Q-factor performance can be easily designed. And it is possible to easily adjust the frequency band for filtering by controlling the operation of the switch included in the image removal filter.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in the drawings, the same components are denoted by the same reference symbols as possible. Further, the detailed description of well-known functions and constructions that may obscure the gist of the present invention will be omitted.

FIG. 1 is a block diagram illustrating a structure of an RF transmitter for performing a conventional conversion of a digital signal into an analog signal and a direct conversion for simultaneously performing frequency up-conversion. As shown in FIG. 1, the RF transmitter for direct conversion includes a direct converter 110, a variable gain amplifier 120, a band pass filter 130, a power amplifier 140, and a power controller 150.

The direct conversion unit 110 receives a signal of a digital base band having different phases (I and Q). The direct conversion unit 110 converts the received digital signal into an analog signal and simultaneously converts the received digital signal into an oscillation frequency into an RF frequency. The structure of the conventional direct conversion unit 110 for this purpose is shown in FIG.

2 is a block diagram showing the structure of a conventional direct conversion unit 110. As shown in FIG. As can be seen in FIG. 2, the conventional direct converter 110 includes a digital-to-analog converter 210 and a local oscillator 220.

In general, a digital-to-analog converter converts an input digital baseband signal into an analog baseband signal. The local oscillator generates oscillation frequencies with different phases and up-converts the frequency of the input signal.

On the other hand, as shown in FIG. 2, the direct converter 110 does not operate independently of the digital analog converter 210 and the local oscillator 220 but simultaneously operates. In other words, when signals having different phases are input, the digital signals are converted into analog signals by the digital-to-analog converter 210, and the frequency is up-converted by receiving the oscillation frequency generated by the local oscillator 220.

In summary, the direct conversion unit 110 receives a digital base vance signal and converts it directly into an analog RF signal. Thereafter, the signals having different converted phases are summed and output to the variable gain amplifier 120 of FIG. 1.

Returning to the description of FIG. 1, the variable gain amplifier 120 receives an analog RF signal from the direct converter 110. The variable gain amplifier 120 automatically controls and amplifies the gain of the received RF signal. Automatic control of the gain of the signal is also called Automatic Gain Control (AGC). The variable gain amplifier 120 outputs the amplified signal to a band pass filter.

The band pass filter 130 receives the amplified signal from the variable gain amplifier 120. The band pass filter 130 filters the signals of the remaining bands except for signals of a desired frequency band. In particular, the band pass filter 130 removes an image signal necessarily generated during the frequency upconversion process.

The power amplifier 140 receives a signal from which the image signal is removed from the band pass filter 130, amplifies the transmission power, and transmits the signal to the antenna.

The power controller 150 controls the operating power of the direct converter 110, the variable gain amplifier 120, and the power amplifier 140, respectively.

1 illustrates the structure of a conventional RF transmitter for performing direct conversion. As described above, although a conventional RF transmitter can directly convert a digital baseband signal to an analog RF signal, an image signal is essentially generated during the frequency upconversion process. The filtering to remove the generated image signal is performed separately in the high frequency RF band after the signal conversion process is finished. This causes a problem of designing a filter having a high level of sharpness value. In the present invention, to solve the above problems.

3 is a diagram illustrating the structure of an RF transmitter according to an embodiment of the present invention. As shown in FIG. 3, the RF transmitter of the present invention includes a digital radio frequency converter (hereinafter referred to as a digital RF converter) including a digital analog converter 320, an image cancellation filter 330, and a mixer 340. ') 310, and an amplifier 350. In FIG. 3, the interior of the digital RF converter 310 is classified according to its function, but it should be noted that the operation occurs substantially simultaneously.

In addition, the digital-to-analog converter 320, the image rejection filter 330, and the mixer 340 of the present invention are characterized in that they are integrated on a single chip.

The digital RF converter 310 converts a digital baseband signal having a different phase into an analog RF signal. According to another embodiment of the present invention, it is also possible to receive a digital intermediate frequency signal instead of the digital base band signal. In addition, the digital RF converter 310 removes a band in which an image signal is generated after the digital base band signal is converted into an analog signal.

In general, an image signal is an signal generated when a frequency rising or falling conversion by a mixer is performed. Accordingly, conventional image signal removal has been performed by removing the image signal generated after the frequency rising or falling conversion by the mixer.

On the contrary, the digital RF converter 310 of the present invention removes a frequency band in which an image signal is expected to be generated after the frequency rising conversion. Therefore, the image signal generated during the frequency up-conversion in the subsequent process may be removed by the removed band.

Hereinafter, the internal structure of the digital RF converter 310 is classified and described according to its function.

The digital-to-analog converter 320 receives digital baseband signals having different phases and converts them into analog baseband signals. According to another embodiment of the present invention, it is also possible to receive a digital intermediate frequency signal instead of the digital base band signal.

The image removal filter 330 removes the frequency band in which the generation of the image signal is expected to remove the image signal generated in the frequency up-conversion process in advance. When the frequency of the baseband signal and the oscillation frequency generated by the local oscillator are set, the frequency band at which the image signal is generated can be estimated. According to this principle, even if the image signal is not generated before the frequency up-conversion process, the generated frequency band can be predicted and filtered in advance.

In addition, the image removal filter 330 may arbitrarily adjust a frequency band for filtering by a combination of switches connected to a capacitor inside the filter. In this case, the switch is operated by a control signal of a controller not shown in the figure.

A feature of the present invention is that the image reject filter 330 is positioned prior to the frequency upconversion by the mixer 340. Therefore, by performing the filtering before the frequency up-conversion, the image rejection filter 330 having the same Q-factor performance can be easily designed.

The mixer 340 is a frequency conversion circuit and receives a frequency of an input signal and an oscillation frequency generated by a local oscillator and generates a signal corresponding to the sum and difference.

In other words, when the frequency f1 of the signal including meaningful data and the oscillation frequency LO generated by the local oscillator are input to the mixer 340, signals of LO + f1 and LO-f1 are generated. In this case, the actual signal to be transmitted by the RF transmitter is LO + f1, and the signal of LO-f1 is an image signal. In the digital RF converter 310 of the present invention, since the frequency band in which the image is generated is filtered by the image removal filter 330, the image signal is not generated.

The above process will be described in detail with reference to FIG. 4.

4 is a diagram illustrating a frequency response illustrating a process of outputting an analog RF signal from which an image signal is removed by the digital RF converter 310 of the present invention.

First, FIG. 4A shows the frequency f1 of a signal containing meaningful data and the oscillation frequency LO generated by the local oscillator in the frequency band. In this case, it is assumed that actual data to be transmitted is included in f1, and f1 is a signal modulated with an analog signal.

FIG. 4B is a diagram illustrating a frequency response of the image removal filter 330 which predicts and removes a frequency band in which an image signal is to be generated by frequency up-conversion. Given a signal f1 including data and an oscillation frequency LO, as shown in FIG. 4A, it can be expected that signals of LO + f1 and LO-f1 will be generated later. In this case, LO + f1 is the signal to be transmitted, and LO-f1 is an unwanted signal, that is, an image signal. Therefore, the image removal filter is set to remove LO-f1, which is a frequency band in which the image signal is generated.

4C is a diagram illustrating a frequency response to a signal generated when the frequency upconversion by the mixer 340 is performed. As described above, when frequency upconversion is performed, signals of LO + f1 and LO-f1 are generated around the oscillation frequency LO.

4D is a diagram illustrating the frequency response of a signal whose signal filtered by the image removal filter 330 is frequency upconverted by the mixer 340.

Combining the diagram of the frequency response shown in FIG. 4B with the diagram of the frequency response shown in FIG. 4C, that is, multiplying the gain of each frequency response, results in only a signal of Lo + f1 being generated. In this case, it can be seen that the image signal LO-f1 is removed by the filtering of the image removal filter 330.

Therefore, the digital RF converter 310 of the present invention may first perform filtering to remove the image signal before frequency up-conversion, thereby generating an analog RF signal from which the image signal is removed.

Returning to the description of FIG. 3 again, the signal passing through the mixer 340 is an analog RF signal from which the image signal has been removed. The mixer 340 outputs the generated RF signal to the amplifier 350.

The amplifier 350 amplifies an analog RF signal output from the digital RF converter 310 and transmits the same through an antenna.

5 is a circuit diagram illustrating a circuit of an image removal filter 330 according to an embodiment of the present invention.

As shown in FIG. 5, the image rejection filter 330 is an LC filter including a capacitor and an inductor. In FIG. 5, a two stage LC filter is illustrated, but the present invention is not limited thereto, and a stage filter larger than that may be used. Using a high stage filter increases the level of rejection of the image signal but complicates the design.

Each capacitor of the image removal filter 33 may be connected to a switch 510 to adjust a frequency band for filtering.

6 is a circuit diagram illustrating an internal circuit of the digital RF converter 310 according to an exemplary embodiment of the present invention. 6 illustrates a connection state of actual circuits of the digital-to-analog converter 320, the image rejection filter 330, and the mixer 340.

First, digital base band signals or intermediate frequency signals having different phases are input to the digital-to-analog converter 320. Then, the input digital signal is converted into an analog base band signal or an intermediate frequency signal.

The analog-converted signal is input to the image removal filter 330. The image removal filter 330 controls the operation of the switch 510 to filter the frequency band in which the generation of the image signal is expected.

The filtered signal is input to the mixer 340. The mixer 340 receives the filtered signal and the oscillation frequency and up-converts the frequency. Here, the image signal generated during the frequency up-conversion is removed at the same time by the image removal filter 330 in the previous step.

A feature of the present invention is that the digital-to-analog converter 320, the image rejection filter 330, and the mixer 340 are integrated on one chip, as shown in FIG. Therefore, there is an advantage that the image removal filter 330 can be reduced in size compared to the structure used outside the converting and mixing module.

7 is a flowchart illustrating a process of converting a digital baseband signal into an analog RF signal from which an image signal has been removed according to an embodiment of the present invention.

First, in step S710, the digital-to-analog converter 320 receives digital baseband signals of different phases. Then, the digital-to-analog converter 320 converts the received digital baseband signal into an analog baseband signal in step S720.

The image rejection filter 330 estimates the generated frequency band of the image signal by using the frequency band of the baseband signal and the frequency band of the oscillation frequency generated by the local oscillator. In operation S730, the image removal filter 330 removes the expected image signal generation region in advance.

In operation S740, the mixer 340 up-converts the frequency of the signal using the oscillation frequency. This produces an analog RF signal with the image signal removed.

Then, the amplifier 350 amplifies the generated RF signal in step S750 and transmits it through the antenna.

It should be noted that the above-described structure of the transmitting apparatus and the order of the transmitting method are logically classified according to their function, and their actual operations occur simultaneously.

The embodiments of the present invention disclosed in the present specification and drawings are merely illustrative of specific embodiments of the present invention and are not intended to limit the scope of the present invention in order to facilitate understanding of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

1 is a block diagram illustrating a structure of an RF transmitter for performing a conventional conversion of a digital signal to an analog signal and a direct conversion for simultaneously performing frequency up-conversion.

2 is a block diagram showing the structure of a conventional direct conversion unit 110. FIG.

3 illustrates the structure of an RF transmitter in accordance with an embodiment of the invention.

4 is a diagram illustrating a frequency response illustrating a process of outputting an analog RF signal from which an image signal is removed by the digital RF converter 310 of the present invention.

5 is a circuit diagram illustrating a circuit of an image rejection filter 330 according to an embodiment of the present invention.

6 is a circuit diagram showing an internal circuit of the digital RF converter 310 according to the embodiment of the present invention.

7 is a flowchart illustrating a process of converting a digital baseband signal into an analog RF signal from which an image signal has been removed according to an embodiment of the present invention.

Claims (8)

A transmitting device for directly converting a digital signal into a radio frequency signal, A digital analog converter which receives digital signals having different phases and converts them into analog signals; An image removal filter for removing a frequency band in which an image signal is expected to be generated when the converted analog signal and the oscillation frequency are mixed; And And a mixer configured to frequency-upconvert the signal from which the image signal generation band is previously removed to a radio frequency band. And said digital-to-analog converter, said image rejection filter and said mixer are integrated on one chip. The method of claim 1, And said image removal filter comprises a switch for adjusting said frequency band to be removed. The method of claim 1, And an amplifier for receiving and amplifying the frequency up-converted signal. The method of claim 1, And the digital signal input to the digital to analog converter is either a digital base band signal or a digital intermediate frequency signal. In the transmission method for directly converting a digital signal into a radio frequency signal, Receiving a digital signal having a different phase and converting the signal into an analog signal; Removing a frequency band in which an image signal is expected to be generated when the converted analog signal and the oscillation frequency are mixed; And And performing a frequency upconversion of the signal from which the image signal generation expected band has been removed in advance to a radio frequency band. The method of claim 5, wherein the removing step, And adjusting the frequency band to be removed. The method of claim 5, And receiving and amplifying the frequency up-converted signal. The method of claim 5, And the digital signal input to the digital to analog converter is either a digital baseband signal or a digital intermediate frequency signal.

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