KR20100060880A - Mixer - Google Patents

Abstract

PURPOSE: A frequency mixer is provided to reduce the probability of an error in an original signal by reducing noises that are caused by an image frequency signal in the demodulation process of the original signal. CONSTITUTION: A driver(310) amplifies the inputted RF(Radio Frequency) signals. The driver filters, among the amplified RF signals, an image frequency signal. A switching unit(320) generates an IF(Intermediate Frequency) signal by temporarily switching the amplified RF signals excluding the image frequency signal according to an inputted LO(Local Oscillator) signal. An output unit(330) outputs the generated IF signal. The driver comprises MOSFET which amplifies the RF signals and also a filter which lets the image frequency signal pass through it.

Description

Frequency Mixer {MIXER}

The present invention relates to a frequency mixer, and more particularly, to a frequency mixer capable of removing an image frequency signal.

In general, the frequency mixer included in the heterodyne RF receiver converts a radio frequency (RF) signal into an intermediate frequency (IF) signal. In detail, the frequency mixer outputs an IF signal corresponding to a difference between a local oscillation (LO) signal and an RF signal provided from a local oscillator.

An image frequency signal other than the RF signal and the LO signal may be input to the frequency mixer of the heterodyne system. Here, the image frequency signal is a signal having a frequency subtracted by the frequency of the IF signal from the frequency of the LO signal. When the image frequency signal is input to the frequency mixer together with the RF signal, the RF signal is converted into an IF signal, and the image frequency signal is also converted into an IF signal. As a result, the frequency mixer outputs one IF signal by the RF signal and the image frequency signal. Since these IF signals contain components by video frequency signals, converting these signals to baseband signals and demodulating them makes it difficult to obtain a desired main signal because noises from video frequency signals are mixed.

In order to solve this problem, in general, an image reject filter was added to the front of the frequency mixer to remove the image frequency signal, which will be described in detail with reference to FIG. 1.

1 is a typical heterodyne RF receiver including an image removal filter.

Referring to FIG. 1, the operation of a typical heterodyne RF receiver including an image removal filter will be described below.

First, the RF receiver receives an RF signal through the antenna 110. Then, the received RF signal passes through the band pass filter 120, and the RF signal passing through the band pass filter 120 is input to the low noise amplifier 130 and amplified. The amplified RF signal passes through an image removal filter 140 that removes an image frequency signal, and the RF signal that passes through the image removal filter 140 is input to the frequency mixer 150. The local oscillation (LO) signal provided from the local oscillator 160 is also input to the frequency mixer 150. Then, the frequency mixer 150 outputs an IF signal corresponding to the difference between the input RF signal and the LO signal.

In a typical heterodyne RF receiver including such an image removal filter, it is fortunate that the image removal filter 140 correctly removes the image frequency signal, but otherwise, the frequency mixer 150 transmits the RF signal and the image frequency signal. Since they are input together, they are a decisive obstacle to demodulation of the original signal. In addition, since the image removal filter 140 is added to the RF receiver, there is a problem in that the overall size of the RF receiver is increased. In addition, there is a cost burden due to the addition of the image removal filter 140.

In addition to the general RF receiver including the image removal filter illustrated in FIG. 1, there are also RF receivers including a Hartley structure and a weaver structure for removing an image frequency signal. However, these RF receivers are also a form of adding an additional filter, so that the overall size of the RF receiver becomes large, and there is a cost burden due to the addition of the filter.

Accordingly, the present invention provides a frequency mixer capable of removing video frequency signals.

In addition, the present invention provides a frequency mixer in the RF receiver to eliminate the need for a secondary filter for removing the image frequency signal.

The frequency mixer according to the present invention includes a driver for amplifying input RF (Radio Frequency) signals and filtering an image frequency signal among the amplified RF signals, and amplified RF signals except for the image frequency signal. It includes a switching unit for generating an IF (Intermediate Frequency) signal by switching in time according to the LO (Local Oscillator) signal, and an output unit for outputting the generated IF signal.

In addition, the driving unit of the frequency mixer according to the present invention preferably includes a MOSFET for amplifying the RF signals input to the gate terminal, and a filter electrically connected between the drain terminal and the ground of the MOSFET and passing an image frequency signal. .

In addition, the filter of the frequency mixer according to the present invention preferably includes an inductor and a capacitor connected in series with each other.

In addition, the capacitor of the frequency mixer according to the present invention is preferably a variable capacitor.

Using the frequency mixer according to the present invention has the advantage of removing the image frequency signal. In addition, the use of the frequency mixer according to the present invention does not require a secondary filter for removing an image frequency signal in the RF receiver, and thus the size of the RF receiver is not increased and the cost burden is not large. have. In addition, when the frequency mixer according to the present invention is used, noise due to an image frequency signal may be reduced during demodulation of an original signal, thereby reducing an error probability of the original signal.

Hereinafter, the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a part obvious to those skilled in the art will be omitted so as not to disturb the gist of the present invention. In addition, it is to be noted that each of the terms described below are only used to help the understanding of the present invention, and may be used in different terms despite the same purpose in each manufacturing company or research group.

In general, there are various types of frequency mixers, which are classified into single-ended frequency mixers and balanced mixers. Equilibrium mixers are further classified into single balanced frequency mixers and double balanced frequency mixers. Here, a Gilbert cell mixer, which is one of the dual balanced frequency mixers, is mainly used. The Gilbert cell frequency mixer of the dual balanced structure has excellent linearity due to improved spurious response due to its structural characteristics, and the matching circuit has a simple advantage. Hereinafter, the Gilbert cell frequency mixer will be described in more detail with reference to FIG. 2.

2 is a circuit diagram of a typical Gilbert cell frequency mixer.

Referring to FIG. 2, the general Gilbert cell frequency mixer includes a driver 210, a switch 220, and an output 230.

The driver 210 includes a pair of amplification elements M1 and M2, amplifies an RF + signal input to the gate terminal of M1, and amplifies an RF- signal input to the gate terminal of M2. Here, the RF + signal and the RF- signal have a phase difference of 180 degrees, and M1 and M2 are implemented as n-channel MOSFET devices.

The switching unit 220 includes a pair of M3 and M4 for switching the output current of M1, and a pair of M5 and M6 for switching the output current of M2. The LO + signal is input from the local oscillator (not shown) to the terminals of the gates of M3 and M6, and the LO- signal is input to the gate terminals of the M4 and M5. Here, the LO + signal and the LO- signal have a phase difference of 180 degrees, and M3, M4, M5, and M6 are implemented as n-channel MOSFET devices. The drain terminal of M4 and the drain terminal of M6 are electrically connected, and the drain terminal of M3 and the drain terminal of M5 are electrically connected. The source terminal of M3 and the source terminal of M4 are electrically connected, and the source terminal of M5 and the source terminal of M6 are electrically connected. The switching unit 220 outputs IF + and IF- signals by mixing RF + and RF- signals amplified by M1 and M2 with LO + and LO- signals.

The output unit 230 outputs the IF + and IF− signals output from the switching unit 220.

The Gilbert cell frequency mixer of the dual balance structure amplifies the RF + signal and the RF- signal input to the driver 210, and converts the amplified RF + signal and the RF- signal to the LO + signal and the LO− input to the switching unit 220. Each of the signals is mixed with the output unit 230 to output an IF + signal and an IF− signal. However, an RF receiver including such a Gilbert cell frequency mixer should have an image rejection filter in front of the frequency mixer, as shown in FIG. This is because the frequency mixer shown in FIG. 2 cannot remove an image frequency signal by itself.

Next, a frequency mixer according to an exemplary embodiment of the present invention capable of effectively removing an image frequency signal without having an image removal filter in a heterodyne RF receiver will be described with reference to FIG. 3. .

3 is a circuit diagram of a frequency mixer according to a preferred embodiment of the present invention.

Referring to FIG. 3, the frequency mixer according to the preferred embodiment of the present invention includes a driving unit 310, a switching unit 320, and an output unit 330.

The driver 310 includes a pair of M1 and M2, two first inductors L1 and a second inductor L2, two first capacitors Cp1, and a second capacitor Cp2. An RF + signal is input to the gate terminal of M1, and an RF- signal is input to the gate terminal of M2. The drain terminals of M1 and M2 are electrically connected. The drain terminal of M1 is electrically connected to the source terminals of M3 and M4 of the switching unit 220. One end of the first inductor L1 is electrically connected to the drain terminal of M1, and the other end thereof is connected to one end of the first capacitor Cp1. The other end of the first capacitor Cp1 is electrically connected to the ground. One end of the second inductor L2 is electrically connected to the drain terminal of M2, and the other end thereof is connected to one end of the second capacitor Cp2. The other end of the second capacitor Cp2 is grounded. As such, the first inductor L1 and the first capacitor Cp1 connected in series resonate only at the frequency of the image frequency signal among the plurality of RF + signals input to the gate terminal of M1. Therefore, the image frequency signal input to the gate terminal of M1 is not input to the switching unit 320, and exits to the ground. As a result, the first inductor L1 and the first capacitor Cp1 connected in series with each other serve as a filter for passing only an image frequency signal. Similarly, the second inductor L2 and the second capacitor Cp2 connected in series also serve as a filter for passing only the image frequency signal.

Here, when the driving unit 310 of the frequency mixer according to the present invention removes only one image frequency, capacitors Cp1 and Cp2 having a specific value may be used. However, in order to selectively remove various image frequency signals, it is preferable to use capacitors Cp1 and Cp2 as variable capacitors, as shown in FIG. 3.

The switching unit 320 includes a pair of M3 and M4 for switching the output current of M1 according to the input LO signal and a pair of M5 and M6 for switching the output current of M2 according to the input LO signal. . The LO + signal is input from the local oscillator to the terminals of the gates of M3 and M6, and the LO- signal is input to the gate terminals of the M4 and M5. Here, the LO + signal and the LO- signal have a phase difference of 180 degrees. Meanwhile, the drain terminal of M4 and the drain terminal of M6 are electrically connected, and the drain terminal of M3 and the drain terminal of M5 are electrically connected. The source terminal of M3 and the source terminal of M4 are electrically connected, and the source terminal of M5 and the source terminal of M6 are electrically connected. The switching unit 320 outputs an IF signal corresponding to the difference between the frequencies of the two signals by mixing the RF signal and the LO signal amplified by M1, M2.

The output unit 330 outputs an IF signal output from the switching unit 320.

Next, an operation of the frequency mixer according to the preferred embodiment of the present invention shown in FIG. 3 will be described.

Signals having various frequencies other than the RF signal of the actual signal desired by the user are input to the driver 310 of the frequency mixer according to the preferred embodiment of the present invention. Because, in general, there is a low noise amplifier in front of the frequency mixer, since the low noise amplifier is a nonlinear element, so the signal input to the low noise amplifier outputs various harmonic signals. Therefore, various RF signals including the RF signal and the image frequency signal of the actual signal desired by the user are input.

Hereinafter, in order to specifically describe the operation of the frequency mixer according to the preferred embodiment of the present invention, the actual RF signal and the image frequency signal desired by the user to the driving unit 310 will be described. Here, the frequency of the RF signal is the sum of the frequency of the LO signal output from the local oscillator and the frequency of the IF signal output from the frequency mixer, and the frequency of the image frequency signal is the frequency of the LO signal minus the frequency of the IF signal. .

When the video frequency signal is input to the gate terminals of M1 and M2 together with the RF signal, M1 and M2 amplify the video frequency signal and the RF signal, respectively. At this time, if the first inductor L1 and the first capacitor Cp1, the second inductor L2 and the second capacitor Cp2 connected in series are set to resonate at the image frequency, the amplified image frequency signal is grounded. Exit to Therefore, only the RF + and RF- signals are input to the switching unit 320, and the image frequency signals are not input. The respective values of the first inductor L1, the first capacitor Cp1, the second inductor L2, and the second capacitor Cp2 are previously determined by the user.

As such, the frequency mixer according to the preferred embodiment of the present invention includes an LC filter that resonates only at the frequency of the image frequency signal in the driving unit 310, thereby eliminating the need for an image removal filter inside the heterodyne RF receiver. There is an advantage.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. The disclosed embodiments should, therefore, be considered in an illustrative rather than a restrictive sense. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a block diagram of a typical heterodyne RF receiver.

2 is a circuit diagram of a typical Gilbert cell frequency mixer.

3 is a circuit diagram of a frequency mixer according to a preferred embodiment of the present invention.

Claims (4)

In the frequency mixer, A driver for amplifying input RF (Radio Frequency) signals and filtering an image frequency signal from the amplified RF signals; A switching unit configured to generate an IF signal by timely switching the amplified RF signals excluding the image frequency signal according to an input LO signal; And an output unit for outputting the generated IF signal. The method of claim 1, wherein the driving unit, A MOSFET for amplifying the RF signals input to a gate terminal; And a filter electrically connected between the drain terminal of the MOSFET and ground, the filter passing the video frequency signal. The method of claim 2, wherein the filter, A frequency mixer comprising an inductor and a capacitor in series with each other. The method of claim 3, wherein the capacitor, Frequency mixer, which is a variable capacitor.

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