JP2746781B2 - Phase shifter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shifter for generating two signals having a phase difference of 90.degree. Used in a modulator of a communication system.

[0002]

2. Description of the Related Art Generally, modulations such as single sideband modulation (SSB), phase modulation (PSK), quadrature amplitude modulation (QAM), amplitude phase modulation (AMPM), and certain types of frequency modulation (FSK). Modulation devices for narrow-band communication systems have 9
It requires two carrier signals with a phase difference of 0 °.

That is, a signal from a local oscillator is converted into two quadrature-phase carrier signals having a phase difference of 90 ° through a 90 ° phase shifter.
Modulate the I and Q channel signals to 90
Two signals having a phase difference of ゜ are generated, the two signals are combined by a power combiner, and transmitted through a band-pass filter. On the receiver side, the received signal is shifted by 90 ° using a 90 ° phase shifter, and the received data is obtained by multiplying the 0 ° received signal and the 90 ° received signal by a mixer.

The following two methods are known as techniques for obtaining two carrier signals having such a 90 ° phase difference, that is, orthogonal signal waves, by an integrated circuit. One method is R
When a current is applied to a capacitor and a resistor connected in series, the voltage between the capacitor terminals has a phase difference of 90 ° with respect to the current, and the voltage between the resistor terminals is in phase with the current. It is based on what is becoming.

Another method is a digital phase shift method,
A signal having a frequency twice as high as the frequency of the input carrier signal is generated, and this signal is used as a clock signal for two T flip-flops. Is set at the falling edge of this clock signal, two signals having the same frequency as the carrier signal having a phase difference of 90 ° are obtained as output signals of each flip-flop.

[0006]

However, each of the above methods has the following features and disadvantages. The RC phase shift method is excellent in that the circuit configuration is simple,
Since there is inevitable parasitic resistance and parasitic capacitance in circuit parts other than the resistor and the capacitor, the obtained phase difference is large due to the relative magnitude of the resistance value R and the capacitance value C of the entire circuit. It has the disadvantage of being dependent. Further, the obtained phase difference changes depending on the operating frequency. Therefore, it is necessary to adjust the relative values of the resistance value R and the capacitance C of the entire circuit, and it is necessary to change the resistance value R and the capacitance of the resistor and the capacitor according to the operating frequency.

On the other hand, the digital phase shift method is excellent in that an inherently accurate phase difference can be obtained. However, since the digital phase shift method requires operation at twice the frequency, a larger current is generally required than the RC phase shift method. There is a disadvantage that it requires. For this reason, a phase shifter based on the principle of the RC phase shift method is used in the modulation device of the communication system.

[0008] Since the amplitude imbalance and the phase error of the quadrature signal directly contribute to the error of the transmission signal, several techniques for removing the error of the quadrature signal have been proposed. For example, as in the invention described in Japanese Patent Application Laid-Open No. 63-119339, a scalar detector is used to calibrate a quadrature phase modulation device. However, the calibration requires detection of an output signal and is complicated. Requires a circuit configuration.

According to the present invention, a relatively small amplitude error and quadrature phase error generated in a phase shifter by the RC phase shift method are eliminated by a simple circuit configuration, and a wide frequency range can be obtained without adjusting resistance and capacitance. It is an object to provide a usable phase shifter.

[0010]

SUMMARY OF THE INVENTION A phase shifter according to the present invention provides a predetermined signal to a capacitor and a resistor connected in series, and detects two signals corresponding to respective terminal voltages of the capacitor so that the amplitude of the signal is substantially equal. 2 that are equal and have a phase difference of approximately 90 °
Approximate phase shifting means for generating two signals, first and second amplitude equalizing means for inputting output signals of the approximate phase shifting means to equalize the amplitudes, and a first amplitude equalizing means. First subtraction means for outputting a signal corresponding to the difference between the output signal and the output signal of the second amplitude equalization means, and the output signal of the first amplitude equalization means and the output of the second amplitude equalization means First adding means for outputting a signal corresponding to the sum of the signals, third and fourth amplitude equalizing means for inputting the output signals of the subtracting means and the adding means and equalizing the amplitude, respectively; A second subtraction means for outputting a signal corresponding to the difference between the output signal of the amplitude equalization means and the output signal of the fourth amplitude equalization means, and the output signal of the third amplitude equalization means and the fourth A second adder for outputting a signal corresponding to the sum of the output signal of the amplitude equalizer and the output signal of the amplitude equalizer. To.

With this configuration, two signals generated by the approximate phase shift means having a simple circuit configuration and having different amplitudes and whose phase difference is not exactly 90 ° are:
First, the amplitudes are exactly equalized by the first and second amplitude equalizing means. Next, as a result of calculating the difference and the sum of the two signals by the first subtracting means and the first adding means, the difference signal and the sum signal have a phase difference of exactly 90 °.

Taking the difference and the sum converts an error in the phase difference into an error in the amplitude.
If the phase difference between the two signals input to the first subtraction means and the first addition means is not exactly 90 °, the difference signal and the sum signal will have errors in their amplitudes. Then, again, the same signal processing is repeated by the third and fourth amplitude equalizing means, the second subtracting means and the second adding means, so that the amplitudes are exactly equal and the phase difference is exactly nine.
Obtain two signals that are 0 °.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an approximate phase shifter based on the above-described RC phase shift method. By outputting the signal 4, the signal is distributed to two phase signals. The amplitude equalizing circuit 5 receives the signal 3 corresponding to the terminal voltage of the capacitor, and the amplitude equalizing circuit 6 receives the signal 4 corresponding to the terminal voltage of the resistor, and equalizes the amplitude of the signal 3 and the signal 4. The amplitude equalizing circuits 5 and 6
Can be realized, for example, by simply clipping each of the input signals 3 and 4 using two nonlinear amplifiers having the same characteristics.

The subtracter 9 outputs the output signal 7 of the amplitude equalizer 5.
And the output signal 8 of the amplitude equalization circuit 6 and outputs a signal 10 representing the difference between them. The adder 11 receives the output signal 7 of the amplitude equalization circuit 5 and the output signal 8 of the amplitude equalization circuit 6 and outputs a sum signal 12.

Further, the signals 10 and 12 are input to amplitude equalizing circuits 13 and 14, respectively, to equalize the amplitudes by clipping, and the difference and sum of the output signals 15 and 16 are obtained by a subtractor 17 and an adder 18. The amplitude equalizing circuit 1
The same as the amplitude equalizing circuits 5 and 6 may be used as 3 and 14, and the same as the subtractor 9 and the adder 11 may be used as the subtractor 17 and the adder 18.

Next, the operation of the phase shifter according to the present embodiment will be described with reference to FIG.
This will be described with reference to FIG. A current signal 2 of a sine wave as shown in FIG. 2A is input to an approximate phase shifter 1, and two signals 3 and 4 are obtained as outputs thereof. As shown in FIG. 2B, the signals 3 and 4 have substantially the same amplitude and a phase difference close to 90 °, but have exactly different amplitudes and the phase difference is not 90 °. The signals 3 and 4 are converted into signals 7 and 8 having the same amplitude as shown in FIG. By taking the difference and the sum of the signals 7 and 8 by the subtracter 9 and the adder 11, the signals 10 and 12 whose phase difference is exactly 90 ° as shown in FIG. 2D are obtained.

To explain this principle, two signals 7 and 8 are converted into two cos wave signals having the same amplitude and a phase difference of 2φ, ie, 2cos (ωt + φ) and 2cos (ωt−
φ). The sum of these two signals is expressed by the following equation.

[0018]

(Equation 1)

The difference is expressed by the following equation.

(Equation 2)

When the results of Equations 1 and 2 are compared, cos
The phase difference between (ωt) and sin (ωt) is exactly 9
It is 0 °, and it can be seen that two signals having a phase difference of 90 ° are accurately obtained as the signals 10 and 12. on the other hand,
The amplitudes of the signals 10 and 12 are 4 sin (φ) and 4 c, respectively.
os (φ), which indicates that the signals have different amplitudes. Therefore, by taking the sum and difference of the input signals 7 and 8, the error in the phase is replaced by the error in the amplitude of the output signals 10 and 12.

Thus, if the input signals 7, 8 are exactly equal in amplitude but the phase difference is not exactly 90 °,
Output signal 1 modified by taking the sum and difference
For 0 and 12, the phase difference is exactly 90 °, but an error occurs in the amplitude. Therefore, the same processing is repeated again by the amplitude equalizing circuits 13 and 14, the subtractor 17, and the adder 18 to remove the phase and amplitude errors, and finally, the amplitudes are exactly equal and the phase difference is accurately calculated. Obtain two signals 19, 20 which are 90 °.

Next, an example of the configuration of a modulator of a communication system using the phase shifter according to the above-described embodiment will be described. In FIG. 3, reference numeral 30 denotes a converter, which converts an input voice into an electric signal and outputs an I-channel modulated signal 31 and a Q-channel modulated signal 32. Reference numeral 33 denotes the phase shifter shown in FIG. 1, which receives the signal of the local oscillator and outputs two carrier signals 19 and 20. This carrier signal 1
9 and 20 have exactly equal amplitudes and exactly 9 phase differences.
0 ° quadrature signal.

The I-channel modulated signal 31 and the Q-channel modulated signal 32 are mixed by mixers 34 and 35 at 0 ° carrier signal 19.
And 90 ° carrier signals 19 and 20, respectively, and combined by a power combiner 36. The output signal of the power combiner 36 is transmitted from the antenna 38 via the band pass filter 37. Therefore, in the modulation device of the communication system using the phase shifter according to the present invention, accurate modulation at a desired frequency is performed without adjusting the phase shifter.

[0024]

As described above, according to the present invention, R
A phase shifter that can be used in a wide frequency range without adjusting resistance and capacitance by removing the amplitude error and quadrature phase error generated in the phase shifter by the C phase shift method with a simple circuit configuration. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a phase shifter according to one embodiment of the present invention.

FIG. 2 is a diagram showing the amplitude and phase of a signal in each section of the phase shifter shown in FIG. 1;

FIG. 3 is a block diagram illustrating a configuration example of a modulation device of a communication system in which the phase shifter illustrated in FIG. 1 is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Approximate phase shifter 5 Amplitude equalization circuit 6 Amplitude equalization circuit 9 Subtractor 11 Adder 13 Amplitude equalization circuit 14 Amplitude equalization circuit 17 Subtractor 18 Adder

Claims (2)

(57) [Claims] 1. A phase shifter (1) comprising a capacitor and a resistor, receiving a predetermined signal and generating two signals having a phase difference, and an output signal (3, 3) of the phase shifter (1). 4), first and second clipping-based amplitude equalization means (5, 6) for equalizing the amplitudes respectively, and an output signal (7) of the first amplitude equalization means (5) and a second Subtraction means (9) for outputting a signal corresponding to the difference between the output signal (8) of the amplitude equalization means (6), the output signal (7) of the first amplitude equalization means (5) and the second signal Adding means (11) for outputting a signal corresponding to the sum of the output signal (8) of the amplitude equalizing means (6); and inputting the output signals of the subtracting means (9) and the adding means (11). third and fourth chestnut equalizing the amplitude
Phase shifter, characterized in that it comprises an amplitude equalizing means (13, 14) by mappings. 2. A subtraction for outputting a signal corresponding to a difference between an output signal (15) of the third amplitude equalization means (13) and an output signal (16) of the fourth amplitude equalization means (14). Means (1
7) an adding means for outputting a signal corresponding to the sum of the output signal (15) of the third amplitude equalizing means (13) and the output signal (16) of the fourth amplitude equalizing means (14). The phase shifter according to claim 1, further comprising (18).