JP2006279171A - Phase shifter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase shifter improved so that a phase difference of two signals may be accurately 90 degrees over a wide frequency range (100MHz to 2GHz) as a principal purpose. <P>SOLUTION: The phase shifter includes: an approximate 90-degree phase shifter 101 for receiving a signal with a prescribed frequency and outputting first and second signals, the amplitudes of which are equal to each other and the phase difference of which is nearly 90 degrees; an adder circuit 102 for outputting a sum of the first and the second signals; and a subtractor circuit 103 for outputting a difference between the first and the second signals. Since two output signals with the same amplitude and the same frequency as that of an oscillated signal and whose phases differ from each other by 90 degrees are obtained from the phase shifter, phase modulation conversion caused by the amplitude modulation is not generated. Since no amplitude equalization circuit is required, the phase shifter produces the two signals with a phase difference of 90 degrees within a broadband frequency range (100MHz to 2GHz) without being limited by a frequency band of phase shift operations. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention generally relates to a phase shifter that generates two signals having a phase difference of 90 ° used in digital communication or the like, and more specifically, a phase difference with high accuracy in a wide frequency range. The present invention relates to a phase shifter improved so that a signal can be obtained.

  In a modulation / demodulation system in digital communication, two carrier signals having a 90 ° phase difference, that is, signals orthogonal to each other, require high accuracy in the phase difference. As a technique for generating this 90 ° phase difference, a phase shifter conventionally proposed is shown in FIG. 9 (see, for example, Patent Document 1).

  Referring to FIG. 9, in a conventional phase shifter, a predetermined signal is applied to a capacitor and a resistor connected in series, and two signals corresponding to the respective terminal voltages are output (hereinafter referred to as an RC phase shift method). Is used). This phase shifter includes an RC phase means 800 for generating two signals having a phase shift amount of about 90 ° and having an amplitude error, and a first phase for equalizing the amplitude by inputting these two signals, respectively. Amplitude equalization means 801 and second amplitude equalization means 802, and a first signal that outputs a signal corresponding to the difference between the output signal of the first amplitude equalization means and the output signal of the second amplitude equalization means. Subtracting means 803, first adding means 804 for outputting a signal corresponding to the sum of the output signal of the first amplitude equalizing means and the output signal of the second amplitude equalizing means, subtracting means 803 and addition It is a 90 ° phase difference generation circuit including a third amplitude equalizing means 805 and a fourth amplitude equalizing means 806 that respectively input the output signals of the means and equalize the amplitude.

  Next, the operation of the conventional phase shifter will be described with reference to FIG. 9 and FIG. A sin-wave current signal 2 as shown in FIG. 10A is input to an approximate phase shifter 800, and two signals 3 and 4 are obtained as outputs thereof. As shown in FIG. 10B, the signals 3 and 4 have substantially the same amplitude and a phase difference close to 90 °. However, the signals 3 and 4 have different amplitudes and the phase difference is not 90 °. The signals 3 and 4 become signals 7 and 8 having the same amplitude as shown in FIG. 10C by the amplitude equalization circuits 801 and 802. By subtracting and summing the signals 7 and 8 by the subtracter 803 and the adder 804, signals 10 and 12 having a phase difference of exactly 90 ° as shown in FIG. 10D are obtained.

  As described above, by using the RC phase shift method for the approximate phase shift means, the obtained phase difference greatly depends on the values of the resistance and the capacitance, and is also easily affected by the parasitic component, and thus is generated. These signals are output as two signals having different amplitudes and whose phase difference is not exactly 90 °. Therefore, in the above conventional example, the first and second amplitude equalization means 801 and 802 equalize the amplitude error. Next, the first subtracting means 803 and the first adding means 804 take the sum and difference, and as a result, the phase difference between the two signals becomes 90 °.

  Another conventional example is shown in FIG. 11 as a technique capable of correcting a phase shift in a 90 ° phase shifter (see, for example, Patent Document 2).

  Referring to FIG. 11, a 90 ° phase shifter according to another conventional example includes an approximate 90 ° phase shifter 900 that obtains an output obtained by shifting the input IN1 by 90 °, and an output signal VOUT1 of the adder circuit 902. The input signal IN1 is configured as a feedback system as a reference signal (a feedback system circuit is configured using an operational amplifier), a synchronous detector 903 for synchronous detection, an output of the synchronous detector 903, and an input signal IN1 A multiplication circuit 901 for multiplication, and an addition circuit 902 for adding the output of the multiplication circuit 901 and the output of the synchronous detector 903 to obtain an output signal VOUT1. In the 90 ° phase shifter configured as described above, the output signal VOUT1 and the input signal IN1 are compared, and the deviation from 90 ° is fed back to the output signal, thereby correcting the deviation of the output phase and accurately. An output signal VOUT1 having a phase difference of 90 ° can be extracted.

Japanese Patent Laid-Open No. 5-110369

JP-A-3-159305

  The phase shifter according to Patent Document 1 is excellent in that the circuit configuration is simple by using the RC phase shift means 800. However, the obtained phase difference strongly depends on the resistance value of the entire circuit and the relative size of the capacitance, and is affected by variations in resistance and capacitor processing accuracy, wiring parasitic resistance, and parasitic capacitance. For this reason, in the case where it is intended to be used in a wide frequency range (100 MHz to 2 GHz), the output phase difference between the two output signals is approximately 90 ° in the wide frequency range, but the output amplitude is ω = 1. It is equivalent only at the frequency of / (RC). For other frequencies, there is a problem that an amplitude error occurs between the two output signals according to a predetermined frequency. Therefore, in order to accurately correspond the frequencies of the two output signals to the desired frequencies, it is necessary to make the amplitudes equal by inputting them to the amplitude equalization means 801 and 802.

  That is, when the RC phase shift means 800 is used as the approximate phase shift means, it is necessary to connect an amplitude equalization circuit between the phase shifter and the adder / subtractor when used in a wide frequency range. This is through an amplitude equalization circuit, and by making the amplitude error of the two output signals equal, the possibility that amplitude modulation (AM) is converted to phase modulation (PM) is reduced. It means to do. In order to solve this problem in a wide frequency range (100 MHz to 2 GHz), it is possible to use an amplitude equalization circuit that can stably operate in all frequency bands.

  However, it is difficult to realize an amplitude equalization circuit that can operate accurately in such a frequency range. Even if it can be realized, if the frequency range is widened, the number of amplitude equalization circuits is increased accordingly, and the scale of the circuit area is increased accordingly. That is, a stable amplitude equalization operation is difficult, and there is a problem that it is difficult to generate a signal having a phase difference of 90 ° in a wide frequency range (100 MHz to 2 GHz).

  Further, in the phase shifter of Patent Document 2, since a feedback system circuit is configured using an operational amplifier, the circuit configuration is complicated, and stable operation at high frequency can be performed with low current consumption. There was no problem.

  The present invention has been made to solve the above-described problems, and is an improved phase shifter so that the phase difference between two signals is exactly 90 ° in a wide frequency range (100 MHz to 2 GHz). The purpose is to provide.

  Another object of the present invention is to provide an improved phase shifter having a simple circuit configuration, low current consumption, and stable operation at high frequencies.

  The phase shifter according to the present invention includes an approximate phase shift means for inputting a signal having a predetermined frequency and outputting first and second signals having the same amplitude and a phase difference of approximately 90 °; An adding means for inputting the first and second signals and outputting a sum of the first signal and the second signal; and a subtraction for outputting a difference between the first signal and the second signal Means.

  According to the present invention, two output signals having the same amplitude and an accurate 90 ° phase difference can be obtained. In addition, since an amplitude equalization circuit is not required between the phase shifter and the adder / subtracter, there is no restriction on the operating frequency range in the 90 ° phase difference generation.

  According to a preferred embodiment of the present invention, the approximate phase shifting means generates a signal source that generates the signal having the predetermined frequency, and a signal having the predetermined frequency that is output from the signal source. A frequency doubler that generates a signal; and a frequency divider that divides the signal output from the frequency multiplier by 2 and outputs the same signal as the signal having the predetermined frequency.

  By using the multiplying / dividing and phase shifting means as the approximate phase shifting means, it is possible to obtain two output signals having the same amplitude of the output signal and having a phase difference of 90 ° almost exactly.

  It is preferable that the doubling means is constructed using an absolute value circuit.

  The doubler may be configured using a multiplier.

  According to a further preferred embodiment of the present invention, the two output signals from the divide-by-2 means have the same amplitude. Since the output signals have the same amplitude, it is not necessary to connect an amplitude equalizing means between the phase shifter and the adder / subtracter.

  According to the present invention, two output signals having the same amplitude and an accurate 90 ° phase difference can be obtained. In addition, since an amplitude equalization circuit is not required between the phase shifter and the adder / subtracter, the phase shifter can be used in a wide frequency range without being restricted by the operating frequency range in the 90 ° phase difference generation. Can be provided.

  In the phase shifter according to the present invention, the frequency of the output signal from the local oscillator is generated as a signal having a doubled frequency by using a doubler circuit, and then from two master-slave flip-flop circuits. Is input to the divide-by-2 circuit. The two signals output from the divide-by-2 circuit have the same frequency as the output from the local oscillator, and two output signals having the same amplitude and a phase difference of approximately 90 ° are obtained (hereinafter, this approximate shift). The phase means is referred to as a multiplication, division, and phase shift method). Further, an addition process and a subtraction process are performed on the two output signals.

  By using the multiplying / dividing and phase shifting means as the approximate phase shifting means, it is possible to obtain two output signals having the same amplitude of the output signal and having a phase difference of 90 ° almost exactly. Further, since the amplitudes of the output signals are the same, it is not necessary to connect an amplitude equalizing means between the phase shifter and the adder / subtracter. Therefore, there is provided a phase shifter capable of realizing a high-precision 90 ° phase difference in a wide frequency range (100 MHz to 2 GHz) of a television receiver or the like without limiting the operating frequency range associated with the amplitude equalization means. can do.

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

  FIG. 1 is a block diagram showing the principal part of a phase shifter according to an embodiment of the present invention, and shows the basic principle of a circuit for generating two signals having a 90 ° phase difference. The phase shifter according to the embodiment includes approximate phase shift means 101, an adder circuit 102, and a subtractor circuit 103.

  The local oscillator 100 supplies a signal having a predetermined frequency to the approximate phase shift means 101. The approximate phase shift means 101 used here is a frequency division / phase shift means described later. The signals obtained by the approximate phase shift means 101 are two signals V1 and V2 having the same amplitude and a phase difference of approximately 90 °, and these signals are supplied to the adding circuit 102 and the subtracting circuit 103.

  The adder circuit 102 adds the signal V1 and the signal V2 and outputs the result as a signal VI. The subtracting circuit 103 subtracts the signal V1 and the signal V2 and outputs the result as a signal VQ.

  FIG. 2 is a specific example of the approximate phase shift means, and shows the basic principle of the multiplication and division method. The approximate phase shift means inputs the output signal from the local oscillator 200 and outputs a signal corresponding to a frequency twice the local oscillation frequency, and a double circuit 201 that inputs the output signal and doubles the output signal. The divide-by-2 circuit 202 outputs a signal having a frequency of ½ as a signal divided by two. By adopting the frequency division and division method, two signals having the same amplitude and a phase different by approximately 90 ° and the same frequency as the signal output from the local oscillator 200 can be obtained.

FIG. 3 is a diagram for explaining the operating principle of 90 ° phase difference generation, and shows the relationship of each signal as a vector. The signal V1 and the signal V2 output from the multiplication / dividing / phase shifting means are signals having the same amplitude and a phase difference of approximately 90 °. The signal VI is a signal obtained by adding the signal V1 and the signal V2, and the signal VQ is a signal obtained by subtracting the signal V2 from the signal V1. This will be described using mathematical expressions.

Outputting the sum and difference of the two input signals by the addition circuit and the subtraction circuit, respectively, means that the following signals are output.

  When the two signals VI and VQ are compared, the phase relationship between sin (ωt) and cos (ωt) is 90 °, so the two signals VI and VQ have a phase difference of exactly 90 °. It can be seen that it is obtained as a signal having.

  Here, an example of how much accuracy the 90 ° phase difference requires is shown. In general, in digital communication or the like, it is an important problem to remove a signal component of an image frequency. As a means for solving this problem, there is a method of attenuating an image signal component using two signal components having a phase difference of 90 °. The attenuation ratio of an image signal component to a desired signal component is expressed as an image removal ratio (Image). It is called Rejection Ratio (IRR). The image rejection ratio is greatly influenced by the accuracy of the amplitude ratio and phase difference of two signals having a phase difference of 90 °, and the same accuracy is required even for a local oscillation signal. If an image rejection ratio of 40 dB is required, the phase difference and amplitude ratio required between two local oscillation signals for realizing this are based on ΔΦ <1 ° and ΔA <1%, respectively. .

When an approximately 90 ° phase difference is generated by using a divide-by-2 unit as the approximate phase shift unit, the phase difference of the output signal is expressed by ΔΦ, which is influenced by the mismatching of elements and the physical distance of the signal path. It is also assumed that ≧ 1 °. Therefore, by using an adder and a subtracter installed at the subsequent stage of the divide-by-2 unit, the phase difference between the two final output signals can satisfy ΔΦ <1 ° by performing phase correction.

As for the amplitude ratio, the amplitude ratio of the output signal is ΔA <1% due to the clipping effect of the divide-by-two means.
The phase difference is corrected within a range that does not exceed.
The above is the reference for the phase difference and amplitude ratio of the local oscillation signal in the 90 ° phase difference generation unit. In actual circuit operation, the performance of the image rejection ratio is determined in consideration of the influence of the mixer and the like. Needless to say.

  FIG. 4 shows another configuration example of a phase shifter that generates a 90 ° phase difference. The signals V1 and V2 output by the approximate phase shift means 401 have a phase difference of approximately 90 °. The two signals V1 and V2 are passed through the adder circuit 402 and the subtractor circuit 403, so that two signals accurately maintaining 90 ° orthogonality are output. However, referring to Equations 3 and 4, when the phase error of the input signal is large (when θ is far from 90 °), the phase error may be output as an amplitude error. Depending on the application, very high accuracy may be required for the phase difference and amplitude. Generally, a mixer is connected to the subsequent stage of a phase shifter used in a communication device or the like, but since this mixer itself has a certain degree of amplitude limiting operation, the amplitude of the output signal is completely the same. You don't have to. However, in the special case as described above, as shown in FIG. 4, by installing the circuits of the amplitude equalizing means 404 and 405 in the subsequent stage of the phase shifter and performing the amplitude limiting operation, the signal obtained is , A signal VI and a signal VQ having a phase difference of 90 ° and the same amplitude can be output. In the present invention, the amplitude equalizing means 404 and 405 are not necessarily required, but the problem can be avoided in this way when two amplitude errors with higher accuracy are required.

  FIG. 5 shows an example of the circuit configuration (absolute value circuit) of the doubler. A signal output from the local oscillator is connected to the bases of input transistors (hereinafter abbreviated as Tr) 501 and 502. The collectors of Tr 501 and 502 are connected to the base of the differential input Tr 504 via a capacitance 522. The emitters of Tr 501 and 502 are connected to the base of the differential input Tr 503 via a capacitance 523. The collectors of differential inputs Tr503 and 504 are connected to the bases of load resistor 516 and load resistor 517, Tr505 and Tr506, respectively. The emitter of Tr505 is connected to the base of the differential input Tr507 via a capacitance 525, and the emitter of Tr506 is connected to the base of the differential input Tr508 via a capacitance 524. The collectors of differential inputs Tr507 and 508 are connected to the bases of load resistor 520 and load resistors 521, Tr509 and Tr510, respectively.

  The output signals OUT and OUTX of such a double circuit 201 are output from the emitters of Tr509 and Tr510, respectively, and a signal of a predetermined frequency output from the local oscillator can be obtained as a signal of a double frequency.

  The multiplication means is not limited to the absolute value circuit described above, and may be a multiplication circuit as shown in FIG. The multiplication circuit is well known and will not be described in detail.

  FIG. 7 shows an example of the circuit configuration of the divide-by-2 means. The connection relationship of these transistors will be described. Among the two signals IN and INX output as signals having a predetermined frequency multiplied by the frequency doubler, the signal IN is connected to the bases of the signal inputs Tr601 and 604, and the signal INX Are connected to the bases of the signal inputs Tr 602 and 603. The power supply voltage VCC is connected to a commonly connected collector of Tr605 and Tr607 via a load resistor 613, and is connected to a commonly connected collector of Tr606 and Tr608 via a load resistor 614. The power supply voltage VCC is connected to a commonly connected collector of Tr609 and Tr611 via a load resistor 615, and is connected to a commonly connected collector of Tr610 and Tr612 via a load resistor 616. The base of Tr 607 is connected to the commonly connected collectors of Tr 606 and Tr 608 and is connected to the base of Tr 609. In addition, the base of Tr608 is connected to the commonly connected collectors of Tr605 and Tr607, and is connected to the base of Tr610. The base of Tr 611 is connected to the collector of Tr 610 and Tr 612 that are commonly connected, and is connected to the base of Tr 606. The base of Tr 612 is connected to the commonly connected collectors of Tr 609 and Tr 611 and is connected to the base of Tr 605. The collector of the signal input Tr601 is connected to the commonly connected emitters of Tr605 and Tr606, and the collector of the signal input Tr602 is connected to the commonly connected emitters of Tr607 and Tr608. The collector of the signal input Tr603 is connected to the commonly connected emitters of Tr609 and Tr610, and the collector of the signal input Tr604 is connected to the commonly connected emitters of Tr611 and Tr612. The commonly connected emitters of the signal inputs Tr601 and Tr602 are grounded via a current source 617, and the commonly connected emitters of the signal inputs Tr603 and Tr604 are grounded via a current source 618.

  In such a divide-by-2 unit 202, the phase relationships of the four-phase output signals I, IB, Q, and QB are extracted as four-phase signals having phase differences of approximately 0 °, 180 °, 90 °, and 270 °, respectively. be able to.

  FIG. 8 shows an example of the circuit configuration of the adding means and the subtracting means. The four-phase output signal I output from the frequency divider means 2 is connected to the bases of the signal inputs Tr 701 and 705, and the signal IB is connected to the bases of the signal inputs Tr 702 and 706. The signal Q is connected to the bases of the signal inputs Tr 703 and 708, and the signal QB is connected to the bases of the signal inputs Tr 704 and 707. The power source is connected to a commonly connected collector of signal inputs Tr 701 and 703 via a load resistor 709, and is connected to a commonly connected collector of signal inputs Tr 702 and 704 via a load resistor 710. The signal input Trs 705 and 707 are connected to a commonly connected collector via a load resistor 711, and the signal input Tr 706 and 708 are connected to a commonly connected collector via a load resistor 712.

  In this way, the output signals VI and VIX of the adder circuit and the subtractor circuit are accurately extracted as four-phase signals having a phase difference of 0 ° and 180 °, and the output signals VQ and VQX are accurately 90 ° and 270 °. it can.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  A phase shifter in which the phase difference between the two signals is precisely 90 ° in a wide frequency range (100 MHz to 2 GHz) can be obtained and used for digital communication and the like.

It is a basic principle diagram of a 90 ° phase difference generation circuit according to an embodiment of the present invention. It is a basic principle figure of the approximate phase shift means used for an Example. It is a figure for demonstrating the operation | movement principle of 90 degree phase difference production | generation. It is a figure for demonstrating the other structural example of a 90 degree phase difference production | generation circuit. It is a figure for demonstrating the example of the circuit structure (absolute value circuit) of the 2 multiplication means used for an Example. It is a figure for demonstrating the example of the other circuit structure (multiplication circuit) of the 2 frequency dividing means used for an Example. It is a figure for demonstrating the example of the circuit structure of the 2 frequency dividing means used for an Example. It is a figure for demonstrating the example of the circuit structure of the addition means and subtraction means used for an Example. It is a simplified block diagram of the conventional phase shifter. It is a figure for demonstrating operation | movement of the conventional phase shifter. It is the simplification block diagram of the other conventional phase shifter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 200 Local oscillator 101 Approximate phase-shift circuit 201 Double circuit 202 Divider circuit 102 Adder circuit 103 Subtractor circuit 404, 405 Amplitude equalization means

Claims (5)

Approximate phase shifting means for inputting a signal of a predetermined frequency and outputting first and second signals having the same amplitude and a phase difference of approximately 90 °;
Adding means for inputting the first and second signals and outputting a sum of the first signal and the second signal;
A phase shifter comprising subtracting means for outputting a difference between the first signal and the second signal. The approximate phase shifting means comprises:
A signal source for generating a signal of the predetermined frequency;
A doubler for generating a signal of a predetermined frequency output from the signal source as a signal of a doubled frequency;
2. The phase shifter according to claim 1, further comprising: a frequency divider that divides the signal output from the frequency doubler by 2 and outputs a signal identical to the signal having the predetermined frequency.   The phase shifter according to claim 2, wherein the doubler means uses an absolute value circuit.   The phase shifter according to claim 2, wherein the multiplication unit uses a multiplier. The phase shifter according to claim 2, wherein the two output signals from the frequency dividing means have the same amplitude.

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