KR20060085006A - Image rejection mixer with secondary image rejection function - Google Patents

Abstract

An object of the present invention is to provide an image reject mixer suitable for a low IF structure of a broadcast receiver.

The image reject mixer of the present invention comprises: first and second mixers for mixing an RF signal with a first local quadrature signal and a first local quadrature signal delayed by 90 degrees from the first local phase signal; Third and fourth mixers for mixing an output signal of the first mixer with a second local quadrature signal and a second local quadrature signal delayed by 90 ° from the second local phase signal; Fifth and sixth mixers for mixing the output signal of the second mixer with a second local quadrature signal and the second local positive phase signal, respectively; An adder for adding output signals of the third mixer and the fifth mixer; A first subtractor which subtracts output signals of the fourth mixer and the sixth mixer; A poly-phase filter for outputting the output signals of the adder and the first subtractor by -45 degrees and +45 degrees; And a second subtractor for subtracting two signals phase shifted by the poly-phase filter.

Terrestrial DMB Receiver, Low IF Tuner, Secondary Image Rejection, Image Rejection Mixer

Description

Image Rejection Mixer with Secondary Image Rejection {IMAGE REJECTION MIXER WITH SECONDARY IMAGE REJECTION FUNCTION}

1 is a block diagram of a conventional heartley structure image reject mixer.

2 is a block diagram of an image reject mixer of a conventional weaver structure.

3 is a block diagram of an image reject mixer of a conventional modified weaver structure.

4 is a block diagram of an image reject mixer according to the present invention.

5 is a frequency spectrum diagram of the RF signal of the present invention.

6 is a vector diagram for explaining phases of input signals of the first and second mixers of the present invention.

7 is a vector diagram for explaining phases of a first local positive phase signal and a quadrature signal according to the present invention.

8 is a vector diagram illustrating phases of output signals of the first and second mixers of the present invention.

9 is a vector diagram for explaining phases of a second local positive phase signal and a quadrature signal according to the present invention.

10 is a vector diagram for explaining phases of output signals of the third and fourth mixers of the present invention.

11 is a vector diagram for explaining phases of output signals of the fifth and sixth mixers of the present invention.

12 is a vector diagram for explaining the phase of an output signal of the adder of the present invention.

13 is a vector diagram for explaining a phase of an output signal of the first subtractor according to the present invention.

14 is a vector diagram for explaining the phase of the output signal of the poly-phase filter of the present invention.

15 is a vector diagram illustrating a phase of an IF signal output from the second subtractor of the present invention.

Explanation of symbols on the main parts of the drawings

101: low noise amplifier 102: bandpass filter

103: RF AGC amplifier 121: first filter

122: second filter 140: the adder

150: first subtractor 160: poly-phase filter

170: second subtractor 180: IF AGC amplifier

M11, M12: first and second mixers M23, M24: third and fourth mixers

M25, M26: fifth and sixth mixer VCO1: first local signal

LO1: first local positive phase signal LO1 ': first local quadrature signal

VCO2: Second local signal LO2: Second local positive phase signal

LO2 ': second local quadrature signal

The present invention relates to an image rejection mixer suitable for a low IF structure of a broadcast receiver. Particularly, in an image rejection mixer having a weaver structure, it is possible to more reliably remove not only the primary image but also the secondary image. As a result, the primary IF can be set high, and the image rejection performance can be further improved, and accordingly, the present invention relates to an image reject mixer having a secondary image rejection function that facilitates design.

In general, with the rapid development of broadcasting and communication environments such as mobile phones and digital televisions, great advances have been made in such system implementation technologies and / or system-based technologies. In this technological development, mobility and portability are urgently required due to convergence of broadcasting and communication.

On the other hand, in a television system, in order to reduce the size as small as possible, the external element should be suppressed as much as possible. The most suitable method is a direct conversion structure and a low IF method, and a low IF structure is most suitable in a terrestrial DMB receiver. .

Some of the conventional image reject mixers applied to such a low IF structure receiver will be described with reference to FIGS.

1 is a block diagram of a conventional heartley structure image reject mixer.

The conventional heartley structure image rejection mixer shown in FIG. 1 comprises an RF mixer stage 11, a polyphase filter 12, and a subtractor 13.

The RF mixer stage 11 includes a first mixer M1 for mixing an RF signal with a local quadrature phase signal LO and a local quadrature phase signal LO ′ delayed by 90 ° from the local positive phase signal LO, respectively. And a second mixer M2. The polyphase filter 12 phase shifts the respective output signals S11 and S12 from the RF mixer stage 11 by + 45 ° and -45 ° to provide the output signals S21 and S22. Is subtracted by the subtractor 13 to output an IF signal.

2 is a block diagram of an image reject mixer of a conventional weaver structure.

The image reject mixer of the conventional weaver structure shown in FIG. 2 includes an RF mixer stage 21, an IF mixer stage 22, and a subtractor 23.

The RF mixer stage 21 mixes an RF signal with a first local positive phase signal LO1 and a first local quadrature phase signal LO1 'that is delayed by 90 ° from the first local positive phase signal LO1, respectively. A first mixer M1 and a second mixer M2 are included. The IF mixer stage 22 converts the respective output signals S11 and S12 from the RF mixer stage 21 by 90 ° from the second local positive phase signal LO2 and the second local positive phase signal LO2. And a third mixer M3 and a fourth mixer M3 mixing with the delayed second local quadrature phase signal LO2 ', respectively. The output signal S21 of the third mixer M3 and the output signal S22 of the fourth mixer M4 are subtracted by the subtractor 23 to eventually output IF.

3 is a block diagram of an image reject mixer of a conventional modified weaver structure.

The conventional modified weaver structure image rejection mixer shown in FIG. 3 includes an RF mixer stage 31, an IF mixer stage 32, a subtractor 7 and an adder 8.

The RF mixer stage 31 mixes an RF signal with a first local positive phase signal LO1 and a first local quadrature phase signal LO1 'that is delayed by 90 ° from the first local positive phase signal LO1, respectively. And a first mixer 1 and a second mixer 2.

The IF mixer stage 32 has a second delayed output signal I from the RF mixer stage 31 by 90 ° from a second local positive phase signal LO2 and the second local positive phase signal LO2. The third mixer 3 and the fourth mixer 4, which respectively mix with the local quadrature phase signal LO2 ', and the output signal Q from the RF mixer stage 31, the second local quadrature phase signal. And a fifth mixer 5 and a sixth mixer 6 for mixing with LO2 'and the second local positive phase signal LO2, respectively.

At this time, the subtractor 7 subtracts the output signals II and QQ of the third mixer 3 and the fifth mixer 5 to output a BBI signal, and the adder 8 is configured to perform the fourth mixer ( 4) and the output signals IQ and QI of the sixth mixer 6 are added to output the BBQ signal.

This conventional image reject mixer has the following problems.

First, in the image reject mixer of the conventional heartley structure shown in FIG. 1, the image removal characteristic is determined by the matching characteristics of each mixer and the poly-phase filter, and in particular, the poly-phase is implemented by a resistor and a capacitor. Therefore, the phase is 90 degrees apart regardless of frequency, but the gain is different in matching characteristics with frequency. Therefore, in order to solve this problem, since several stages are used, the area is large and the signal attenuation becomes large, and thus there is a problem in terms of noise and power consumption.

In the image reject mixer of the conventional weaver structure illustrated in FIG. 2, there is a problem in that a secondary image signal is generated in an IF mixer stage, and a band pass filter must be further provided to remove the secondary image. There is this. In addition, since the IF frequency is low within a few MHz in the low IF receiver, the selectivity (Q) of the bandpass filter should be high even if an additional bandpass filter is used. There is a problem that is difficult to do.

In the image rejection mixer of the conventional modified weaver structure shown in FIG. 3, there is a problem in that a secondary image signal is generated in the IF mixer stage, and in order to remove the secondary image, a bandpass filter must be further provided. have. In addition, since the IF frequency is low in the low IF structure within a few MHz, the selectivity (Q) of the bandpass filter must be high even if an additional bandpass filter is used. Difficult problems still exist.

The present invention has been proposed to solve the above problems, the object of which is to implement a more reliable removal of the primary image, as well as the secondary image in the image rejection mixer of the weaver structure, high primary IF It is possible to further improve image rejection performance, thereby providing an image rejection mixer having a secondary image elimination function that facilitates design.

In order to achieve the above object of the present invention, the image reject mixer of the present invention,

First and second mixers for mixing an RF signal with a first local quadrature signal and a first local quadrature signal delayed by 90 degrees from the first local phase signal;

Third and fourth mixers for mixing an output signal of the first mixer with a second local quadrature signal and a second local quadrature signal delayed by 90 ° from the second local phase signal;

Fifth and sixth mixers for mixing the output signal of the second mixer with a second local quadrature signal and the second local positive phase signal, respectively;

An adder for adding output signals of the third mixer and the fifth mixer;

A first subtractor which subtracts output signals of the fourth mixer and the sixth mixer;

A poly-phase filter for outputting the output signals of the adder and the first subtractor by -45 degrees and +45 degrees; And

A second subtractor which subtracts two signals phase shifted by the poly-phase filter

Characterized in that it comprises a.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the drawings referred to in the present invention, components having substantially the same configuration and function will use the same reference numerals.

4 is a block diagram of an image reject mixer according to the present invention.

Referring to FIG. 4, the image reject mixer according to the present invention includes a first local quadrature signal delayed by 90 ° from a first local positive phase signal LO1 and the first local positive phase signal LO1. First and second mixers M11 and M12 mixed with LO1 ', and an output signal S21 of the first mixer M11 to a second local positive phase signal LO2 and the second local. Third and fourth mixers M23 and M24 respectively mixing with the second local quadrature signal LO2 'delayed by 90 ° from the positive phase signal LO2, and the output signal S22 of the second mixer M12. And fifth and sixth mixers M25 and M26 for mixing with a second local quadrature signal LO2 ′ and the second local positive phase signal LO2, and the third mixer M23 and the third agent. An adder 140 that adds output signals S41 and S43 of the fifth mixer M25, and a first signal that subtracts output signals S42 and S44 of the fourth mixer M24 and the sixth mixer M26. A subtractor 150, the adder 140, and the first subtractor 150. A poly-phase filter 160 which phase shifts the output signals S51 and S52 by -45 ° and + 45 °, and subtracts two signals that are phase-shifted by the poly-phase filter 160; 2 subtractor 170.

The image reject mixer includes a low noise amplifier 101 for amplifying the received RF signal with a predetermined gain at low noise and a bandpass filter 102 for passing the output signal of the low noise amplifier 101 to a predetermined band. And an RF AGC amplifier 103 for amplifying the output signal of the band pass filter 102 and outputting the amplified output signal to the first and second mixers M11 and M12 according to the output signal strength of the band pass filter 102. ) May be further included.

The image reject mixer passes the first filter 121 for passing the output signal of the first mixer M11 to a preset band and the output signal of the second mixer M12 to a preset band. The second filter 122 may be further included.

The image reject mixer may further include an IF AGC amplifier 180 that amplifies the output signal of the second subtractor 170 according to the output signal strength of the second subtractor 170.

Hereinafter, the operation and effects of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 4, in the image reject mixer of the present invention, the low noise amplifier 101 amplifies a received RF signal with a predetermined gain at low noise in order to increase reception sensitivity. The bandpass filter 102 passes the output signal of the low noise amplifier 101 to a predetermined band. This serves to remove an image at the input side in order to increase the removal rate of the primary image signal. When the input signal is large, the RF AGC amplifier 103 applies a signal larger than the linear region of the receiver to prevent distortion from occurring, according to the output signal strength of the bandpass filter 102. The output signal of the pass filter 102 is amplified and output to the first and second mixers M11 and M12.

Meanwhile, in the description of the present invention, coswLO1t and coswLO2t are first and second local signals, coswIF1t and coswIF2t are first and second IF signals, and a desired signal input to a reception signal input terminal is DES, the desired signal ( The primary image signal of DES) is IM1, the secondary image signal of the desired signal DES is defined as DESI, and the secondary image signal, which is an image signal to the primary image signal IM1, is defined as IM1I. It is assumed that the amplitude of the local signal input to the input terminal of the signal is one.

5 is a frequency spectrum diagram of the RF signal of the present invention.

Referring to FIGS. 4 and 5, the RF signal includes DES and IM1 having a frequency interval equal to "IF1" and a second local positive phase signal LO2 around the first local positive phase signal LO1. DESI having a frequency interval equal to DES and "IF2" at the center, and IM1I having a frequency interval equal to IM1 and "IF2" around the second local positive-phase signal LO2, which is represented by Equation 1 below. It can be expressed as

6 is a vector diagram for explaining phases of input signals S11 and S12 of the first and second mixers of the present invention. 4 to 6, phases of the input signals S11 and S12 input to the first and second mixers M11 and M12 are the same, and each includes DES, IM1, DESI, and IM1I. .

FIG. 7 is a vector diagram for explaining phases of the first local positive phase signal LO1 and the quadrature phase signal LO1 'of the present invention.

4 to 7, when the first local signal is referred to as VCO1, the first local positive phase signal LO1 and the first local quadrature signal LO1 'have a 90 ° phase difference with each other. , May be expressed as Equation 2 below.

The first mixer M11 of the present invention mixes the above RF signal with the first local positive phase signal LO1 and outputs the first IF signal S21. The second mixer M12 of the present invention mixes the RF signal with the first local quadrature signal LO1 ′ delayed by 90 ° from the first local positive phase signal LO1 to mix the first IF signal S22. Output That is, the output signal S21 of the first mixer M11 may be expressed by Equation 3 below, and the output signal S22 of the second mixer M12 may be expressed by Equation 4 below.

8 is a vector diagram for explaining phases of the output signals S21 and S22 of the first and second mixers of the present invention. 4 to 8, the phases of the output signal S21 of the first mixer M11 and the output signal S22 of the second mixer M12 are as shown in FIG. 8.

Next, the first filter 121 of the present invention passes the output signal S21 of the first mixer M11 in a predetermined band, and the second filter 122 passes the second mixer M12. Pass through the output signal S22 of the band.

9 is a vector diagram for explaining phases of the second local positive phase signal LO2 and the quadrature phase signal LO2 'of the present invention. 4 to 9, when the second local signal is referred to as VCO2, the second local positive phase signal LO2 and the first local quadrature signal LO2 'have a 90 ° phase difference with each other. , May be expressed as Equation 5 below.

Next, the third mixer M23 of the present invention mixes the output signal S31 of the first filter 121 with the second local positive phase signal LO2. In addition, the fourth mixer M24 mixes the output signal S32 of the second filter 122 with the second local quadrature signal LO2 'which is delayed by 90 ° from the second local positive phase signal LO2. do.

That is, the output signal S41 of the third mixer M23 may be expressed by Equation 6 below, and the output signal S42 of the fourth mixer M24 may be expressed by Equation 7 below.

10 is a vector diagram for explaining phases of the output signals S41 and S42 of the third and fourth mixers of the present invention. 4 to 10, the phases of the output signal S41 of the third mixer M23 and the output signal S42 of the fourth mixer M24 are as shown in FIG. 10.

In addition, the fifth mixer M25 of the present invention mixes the output signal S22 of the second mixer M12 with the second local quadrature signal LO2 '. The sixth mixer M26 of the present invention mixes the output signal S22 of the second mixer M12 with the second local positive phase signal LO2.

That is, the output signal S43 of the fifth mixer M25 may be expressed by Equation 8 below, and the output signal S44 of the sixth mixer M26 may be expressed by Equation 9 below.

11 is a vector diagram for explaining phases of the output signals S43 and S44 of the fifth and sixth mixers of the present invention. 4 to 11, the phases of the output signal S43 of the fifth mixer M25 and the output signal S44 of the sixth mixer M26 are as shown in FIG. 11.

The adder 140 of the present invention adds the output signals S41 and S43 of the third mixer M23 and the fifth mixer M25 as shown in Equations 6 and 8 above.

That is, when the output signal S41 of the third mixer M23 and the output signal S43 of the fifth mixer M25 are added, IM1 and IM1I are removed, and the output signal is DES as shown in Equation 10 below. And DESI components.

12 is a vector diagram for explaining the phase of the output signal S51 of the adder of the present invention.

4 to 12, the adder 140 adds an output signal S41 of the third mixer M23 and an output signal S43 of the fifth mixer M25 to add a signal S51. The phase of this output signal S51 is as shown in FIG.

 The first subtractor 150 of the present invention subtracts the output signals S42 and S44 of the fourth mixer M24 and the sixth mixer M26 as shown in Equations 7 and 9.

That is, when the output signal S42 of the fourth mixer M24 and the output signal S44 of the sixth mixer M26 are added, IM1 and IM1I are removed, and the output signal is DES as shown in Equation 11 below. And DESI components.

FIG. 13 is a vector diagram for explaining the phase of the output signal S52 of the first subtractor of the present invention.

4 to 13, the first subtractor 150 adds an output signal S42 of the fourth mixer M24 and an output signal S44 of the sixth mixer M26 to add a signal S52. ), The phase of this output signal S52 is as shown in FIG.

The poly-phase filter 160 of the present invention provides an output signal S61 as shown in Equation 12 by shifting the output signal S51 of the adder 140 by -45 °, and the first subtractor ( The output signal S52 of 150 is approximately + 45 ° phase shifted to provide an output signal S62 as shown in Equation 13 below.

14 is a vector diagram for explaining phases of the output signals S61 and S62 of the poly-phase filter of the present invention. 4 to 14, the poly-phase filter 160 phases the output signals S51 and S52 of the adder 140 and the first subtractor 150 by -45 ° and + 45 °. By shifting, signals S61 and S62 having a phase as shown in FIG. 14 are output.

The second subtractor 170 of the present invention subtracts two signals S61 and S62 phase shifted by the poly-phase filter 160 to remove DESI, which is a secondary image signal of a desired signal. As shown in Equation 14, a signal S71 including a DES component that is a desired signal is output.

15 is a vector diagram for explaining the phase of an IF signal output from the second subtractor 170 of the present invention. 4 to 15, when two shifted signals S61 and S62 shown in FIG. 14 are subtracted, a signal including a DES component having a phase as shown in FIG. 15 is output.

In addition, the IF AGC amplifier 180 of the present invention amplifies the output signal of the second subtractor 170 according to the output signal strength of the second subtractor 170 and outputs an IF signal including only the DES component. .

In the image rejection mixer of the present invention described above, it can be seen that not only the primary image but also the secondary image is more reliably removed.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, but is defined by the claims, and the apparatus of the present invention may be substituted, modified, and modified in various ways without departing from the spirit of the present invention. It is apparent to those skilled in the art that modifications are possible.

According to the present invention as described above, in the image reject mixer of the weaver structure suitable for the low IF structure of the broadcast receiver, the primary IF is implemented by more reliably removing not only the primary image but also the secondary image. It can be set higher, it is possible to further improve the image removal performance, thereby making it easy to design.

Claims (4)

First and second mixers for mixing an RF signal with a first local quadrature signal and a first local quadrature signal delayed by 90 degrees from the first local phase signal; Third and fourth mixers for mixing an output signal of the first mixer with a second local quadrature signal and a second local quadrature signal delayed by 90 ° from the second local phase signal; Fifth and sixth mixers for mixing the output signal of the second mixer with a second local quadrature signal and the second local positive phase signal, respectively; An adder for adding output signals of the third mixer and the fifth mixer; A first subtractor which subtracts output signals of the fourth mixer and the sixth mixer; A poly-phase filter for outputting the output signals of the adder and the first subtractor by -45 degrees and +45 degrees; And A second subtractor which subtracts two signals phase shifted by the poly-phase filter Image rejection mixer with a secondary image removal function comprising a. The image reject mixer of claim 1, wherein the image reject mixer A low noise amplifier for amplifying the received RF signal with a predetermined gain at low noise; A band pass filter for passing the output signal of the low noise amplifier to a predetermined band; And RF AGC amplifier for amplifying the output signal of the band pass filter and outputting the output signal to the first and second mixers according to the output signal strength of the band pass filter Image rejection mixer having a secondary image removal function, characterized in that it further comprises. The image reject mixer of claim 1, wherein the image reject mixer A first filter passing the output signal of the first mixer in a preset band; And A second filter for passing the output signal of the second mixer in a preset band; Image rejection mixer having a secondary image removal function, characterized in that it further comprises. The image reject mixer of claim 1, wherein the image reject mixer An IF AGC amplifier for amplifying the output signal of the second subtractor according to the output signal strength of the second subtractor Image rejection mixer having a secondary image removal function, characterized in that it further comprises.

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