JPH06188679A - Phase shift circuit - Google Patents

Abstract

PURPOSE:To prevent an error in component values from giving effect on an output phase difference by connecting a resistive element and a capacitive element in series, connecting a 1st amplitude limit circuit across a resistive element and connecting a 2nd amplitude limit circuit across the capacitive element. CONSTITUTION:When one electrode of a capacitive element 3 connects with ground, a phase of a current flowing to a ground parasitic capacitor 7 at a ground point of the capacitive element 3 and a resistive element 2 is equal to a phase of a current IR flowing to the resistive element 2. Since the component whose phase is equal to the phase of the current IR does not give effect on a phase error, the effect of the ground parasitic capacitance 7 onto the phase error is avoided. In this case, the phase shift circuit with high accuracy is formed by connecting the resistive element to a terminal having a least ground parasitic capacitance among both terminals of the capacitive element 3. Furthermore, since only one each of the resistive element 2 and the capacitive component 3 is employed, the power utilizing efficiency is excellent and the current consumption of the phase shift circuit is reduced and the estimate of the phase shift error in the circuit design stage is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift circuit used in an amplitude / phase modulator and a demodulator, and more particularly to a phase shift circuit suitable for being configured as an integrated circuit.

[0002]

2. Description of the Related Art As a conventional phase shift circuit, a bridge type phase shift circuit as shown in FIG. 5 is often used. In FIG. 5, when the resistance elements 52 and 55 have the same resistance value and the capacitance elements 53 and 54 have the same capacitance value, the resistance element 5
The current I1 flowing through 2 and the current I2 flowing through the capacitive element 54 have the same amplitude and phase. At this time, a voltage having the same phase as the current I2 is generated at the terminal 57, and a voltage having a phase difference of 90 ° from the current I1 is generated at the terminal 56. Therefore, comparing the potentials of the terminals 56 and 57, although the amplitudes vary depending on the frequencies, the phases are 90 ° with respect to each other.
Different signals can be obtained.

However, in the bridge type phase circuit, when the resistance element and the capacitance element forming the bridge are equal, the potential difference between the terminals 56 and 57 is exactly 90 °, but in reality, the resistance element, Since the capacitive element has an error, the values are not always equal and the phase difference deviates from 90 °.

When implementing a phase shifter inside an integrated circuit, the relative error of the element is considered to be small. However, the relative error depends on the processing accuracy, so that the smaller the occupied area of the element, the larger the relative error. It is in. Therefore, in order to obtain a highly accurate phase shift circuit, it is necessary to use an element having a large occupied area. This goes against the demand for higher integration.

Further, currents flow out from the terminals 56 and 57 due to the next-stage circuit connected to the terminals 56 and 57, but even if the magnitudes of the currents flowing out from the respective terminals are different, , 57, the phase difference of the electric potentials generated is not exactly 90 °. Generally, since the input impedance of the circuit connected to the next stage is not always equal, the accuracy of the output phase difference of the phase shift circuit may not be guaranteed depending on the connected circuit.

In an integrated circuit, a capacitance element having a large occupied area has a large capacitance value, so that a large current proportional to the capacitance value is required to obtain a voltage with a large amplitude. This goes against the demand for lower power consumption.

[0007]

As described above,
In the conventional bridge type phase shift circuit, there is a problem that the phase difference of the output signals is not constant because the element values of the resistance element and the capacitance element forming the bridge are not necessarily equal. The present invention provides a phase circuit in which the error in the element value does not affect the output phase difference.

[0008]

According to the present invention, a resistance element and a capacitance element connected in series with the resistance element,
A phase shift circuit comprising a first amplitude limiting circuit connected to both ends of the resistance element and a second amplitude limiting circuit connected to both ends of the capacitance element.

Also, in the first invention, there is provided a phase shift circuit comprising an input signal amplifier circuit for amplifying an input signal to an amplitude necessary for the operation of the first and second amplitude limiting circuits. provide.

Further, in the second invention, the first buffer amplifier circuit is connected to the resistance element, the capacitance element connected in series to the resistance element, and the connection point of the resistance element and the capacitance element. A second buffer amplifier circuit connected to the terminal of the resistance element opposite to the connection point, a third buffer amplifier circuit connected to the terminal of the capacitance element opposite to the connection point, and Amplitude limiting circuit having an input voltage that is the difference between the output voltage of the buffer amplifying circuit and the output voltage of the second buffer amplifying circuit, and the output voltage of the first buffer amplifying circuit and the output of the third buffer amplifying circuit. A second amplitude limiting circuit having a voltage difference as an input voltage, and the absolute values of the input impedances of the first, second and third buffer amplifier circuits are the same as those of the first and second amplitude limiting circuits. Phase shift characterized by being greater than the absolute value of the input impedance To provide the road. Also, the first and second
The invention provides a phase shift circuit in which one terminal of the capacitance element is grounded in an alternating current.

[0011]

The phase shift circuit of the present invention is characterized in that the resistance element and the capacitance element are connected in series. A current with the same amplitude and phase flows in the resistance element and the capacitance element connected in series, so a voltage with the same current and phase is generated at both ends of the resistance element with the phase of this current as a reference, A voltage with a phase difference of 90 ° from the current is generated at both ends. Therefore, when the terminal voltage of the resistance element and the terminal voltage of the capacitance element are compared, it is possible to generate signals with exactly 90 ° different phases.

In the case of the present invention, even if the element values of the resistance element and the capacitance element are different from the design values, the amplitude value of the voltage generated across the resistance element and the capacitance element is different from the design value.
It has no effect on the phase of the voltage across each element.

Further, by providing an amplitude limiting circuit having a high input impedance at both ends of the resistance element and the capacitance element, a constant current is supplied to the resistance element and the capacitance element regardless of the circuit connected to the next stage of the phase shift circuit. Therefore, it is possible to further reduce power consumption.

[0014]

First, the outline of the phase shift circuit of the present invention will be described.
In the present invention, one resistance element and one capacitance element connected in series are used. That is, an amplification circuit that amplifies a sine wave input signal, a resistance element connected to the output terminal of the amplifier, a capacitive element connected in series with the resistance element, and a voltage across the resistance element are input, It is composed of an amplitude limiting circuit that amplifies and outputs the amplitude, and an amplitude limiting circuit that inputs the voltage across the capacitive element and amplifies and outputs it to a constant amplitude.

For example, a signal input from a sine wave signal source is supplied to a resistance element having a resistance value R and a capacitance element 3 having a capacitance value C, which are connected in series. The first amplitude limiting circuit is connected to both ends of the resistance element having the resistance value R, and the second amplitude limiting circuit is connected to both ends of the capacitance element having the capacitance value C. That is, the first of sufficiently large input impedance,
The second amplitude limiting circuit inputs the voltage between terminals of the resistance element and the voltage between terminals of the capacitance element, respectively, amplifies the voltage between terminals of the resistance element and the voltage between terminals of the capacitance element to a certain amplitude, and outputs it. To do. At this time, if the current flowing through the resistance element is IR and the terminal voltage of the resistance element is VR, I
The relationship between R and VR is expressed by Equation 1.

[0016]

[Equation 1]

When the signal current flowing from the connection point between the resistance element and the capacitance element connected in series is Δi and the voltage between the terminals of the capacitance element is VC, the relation between Δi and VC is expressed by the equation (2).

[0018]

[Equation 2] Further, when the phase shift difference between the voltage VR between terminals of the resistance element and the voltage VC between terminals of the capacitance element is φ, φ can be expressed by Equation 3.

[0019]

[Equation 3] Here, when Δi is sufficiently smaller than the current IR flowing through the resistance element, the deviation of the phase difference between VR and VC from 90 ° is Δφ.
Then, Δφ can be approximated by Equation 4.

[0020]

[Equation 4]

That is, if the input impedance of the amplitude limiting circuit including the parasitic capacitance and the like is known, the element values of the capacitive element and the resistive element necessary for keeping the phase error in the terminal voltage within the target value can be determined.

In the present invention, since there is only one resistance element and one capacitance element, there is no influence of relative accuracy.
The resistance value and the capacitance value are set so that the amplitudes are uniform at a desired frequency, but the error affects only the difference between the terminal voltages and does not affect the phase error. Further, since the amplitude difference of the voltage between the terminals is absorbed by the connected amplitude limiting circuits, the error of the element value becomes irrelevant to the output.

In such a series circuit of resistors and capacitors, it is necessary to take out an output as a differential signal, but in an integrated circuit, an amplifier is usually a differential amplifier circuit and an analog multiplication circuit used in a modulator / demodulator. Also, since differential input is usually required, it is rather convenient. Further, as described later, if an amplitude limiting circuit with high input impedance is used, it is possible to make the current flowing out from the connection point between the resistance element and the capacitance element extremely small, and the phase error can be dramatically reduced. it can. Compared to the bridge type phase circuit, there is no problem of relative accuracy of the elements, and since each of the resistance element and the capacitance element has one, the utilization efficiency of the signal power is high and the power consumption can be reduced accordingly.

When this circuit is realized as an integrated circuit,
A capacitive element is often realized by facing two electrodes parallel to a semiconductor substrate. Particularly in the case of a silicon semiconductor, since the substrate is maintained at the positive or negative potential of the DC power supply, there is a large difference in the parasitic capacitance between the two electrodes of the capacitive element. As shown in Expression 4, in the circuit of FIG. 1, the smaller Δi is, the smaller the phase error is. Δi also includes the current flowing in the parasitic capacitance at the connection point between the resistance element and the capacitance element. Therefore, of the two electrodes of the capacitive element, a phase circuit having a smaller phase error can be obtained by connecting the electrode having the smaller parasitic capacitance to ground to the resistor. Hereinafter, a configuration example of the phase shift circuit of the present invention will be described with reference to the drawings.

FIG. 1 shows a first embodiment of the phase shift circuit of the present invention. When one of the electrodes of the capacitive element is grounded in this way, the phase of the current flowing through the parasitic capacitance 7 to the ground at the connection point between the capacitive element and the resistive element becomes equal to the phase of the current IR flowing through the resistive element. From Equation 4, since the component of Δi having the same phase as IR does not affect the phase error, it is possible to avoid the influence of the ground parasitic capacitance 7 on the phase error. In this case, by connecting the resistance element to one of the terminals of the capacitive element having a smaller parasitic capacitance to ground, a more accurate phase shift circuit can be configured.

FIG. 2 shows a second embodiment of the phase shift circuit of the present invention. Particularly in the case of a high-frequency integrated circuit, it is difficult to obtain input / output isolation, so that a large input signal is often required with a small input signal. If the voltage between the terminals of the resistance element and the capacitance element is small, it may be possible to satisfy the signal amplitude requirement by increasing the gain by using a multi-stage amplifier in the amplitude limiting circuit, but there is a phase shift in the amplitude limiting circuit. It becomes a problem.

The problem is that the input signal amplifying circuit 8 is used to increase the signal input to the series circuit of the resistance element and the capacitance element as shown in FIG. 2, and the amplitude limiting circuit has a simple structure with little phase shift. It can be avoided by adopting one.

FIG. 3 shows a third embodiment of the phase shift circuit of the present invention. When the input impedance of the amplitude limiting circuit is not sufficiently large, there is a method of reducing the impedance of the series circuit of the resistance element and the capacitance element to suppress the phase error. However, the buffer amplifier circuits 9 and 10 having a high input impedance such as the emitter follower circuit are available. , 11 can also be used.

FIG. 4 shows a fifth embodiment of the phase shift circuit of the present invention. When a buffer amplifier circuit such as an emitter follower circuit is provided with a capacitive load such as a wiring parasitic capacitance, the output phase may be delayed from the input signal phase particularly at high frequencies. As shown in FIG. 4, buffer amplifier circuits 12, 13, 1
By aligning the loads including the wiring parasitic capacitances of the output terminals 4 and 15, the phase delays in the buffer amplifier circuits can be aligned, and the phase error can be reduced. As described above, according to the present invention, the current consumption of the phase shift circuit can be reduced, and the phase error can be easily estimated at the circuit design stage.

[0030]

As described above, according to the present invention, the resistance element,
A phase shifter that is less affected by the error of the capacitive element can be configured. Further, since there is only one resistive element and one capacitive element, the power use efficiency is better and the current consumption of the phase shift circuit can be reduced compared to a bridge type phase shift circuit that requires at least two. There is also an advantage that the phase shift error can be easily estimated at the circuit design stage.

[Brief description of drawings]

FIG. 1 shows a first embodiment of a phase shift circuit according to the present invention.

FIG. 2 is a second embodiment of the phase shift circuit according to the present invention.

FIG. 3 shows a third embodiment of the phase shift circuit according to the present invention.

FIG. 4 is a fourth embodiment of the phase shift circuit according to the present invention.

FIG. 5 is a conventional phase shift circuit.

[Explanation of symbols]

 1 signal source 2 resistance element 3 capacitance element 4, 5 amplitude limiting circuit

Claims (4)

[Claims] 1. A resistive element, a capacitive element connected in series to the resistive element, and a first element connected to both ends of the resistive element.
And a second amplitude limiting circuit connected to both ends of the capacitive element. 2. The phase shift circuit according to claim 1, further comprising an input signal amplifier circuit for amplifying an input signal to an amplitude required for the operation of the first and second amplitude limiting circuits. 3. A resistance element, a capacitance element connected in series to the resistance element, a first buffer amplifier circuit connected to a connection point between the resistance element and the capacitance element, and a connection point opposite to the connection point. A second buffer amplifier circuit connected to the terminal of the resistance element, a third buffer amplifier circuit connected to the terminal of the capacitance element opposite to the connection point, and an output voltage of the first buffer amplifier circuit And a first amplitude limiting circuit that uses the difference between the output voltages of the second buffer amplifier circuit as an input voltage, and the difference between the output voltage of the first buffer amplifier circuit and the output voltage of the third buffer amplifier circuit as the input voltage. And a second amplitude limiting circuit, the absolute value of the input impedance of the first, second, and third buffer amplifier circuits is greater than the absolute value of the input impedance of the first and second amplitude limiting circuits. Phase shift circuit characterized by being large. 4. The phase shift circuit according to claim 1, wherein one terminal of the capacitance element is grounded in an alternating current.