JP2957796B2 - Phase shift circuit - 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 shift circuit for changing the phase of an input signal by 90 degrees.

[0002]

2. Description of the Related Art A circuit for shifting the phase of an input signal by 90 degrees
For example, it is disclosed in JP-A-59-379. This type of phase shift circuit is used to process various signals. A conventional phase shift circuit of this kind is configured as shown in FIGS. 1, 2 and 3, for example.

[0003] The phase shift circuit shown in FIG.
a, a series circuit of a resistor R _A and R _B between 1b is interposed, the series circuit of the series circuit of the resistor R _A and R _B and the resistor R ₀ and capacitor C ₀ is connected in parallel I have. Resistance R ₀
A connecting portion of the capacitor C ₀ is connected to one side voltage output terminal 1c, resistor R _A and the connection of the R _B is the other side voltage output terminal
Connected to 1d. This phase shift circuit comprises resistors _RA and R
_{By making B the} same resistance value and making the resistance R ₀ equal to the absolute value of 1 / (ωC ₀ ), the input voltage e _i and the output voltage e ₀
Becomes 90 degrees.

[0004] phase-shift circuit shown in FIG. 2, one side voltage input terminal 1a is connected to the base of the transistors T ₁ through the capacitor C _1, the other side voltage input terminal 1b is grounded.
Power V collector of transistors T ₁ via the resistor R ₀
It is connected to the _CC, and its emitter is grounded through a series circuit of a transistor T ₂ and the resistor R _3. Based transistors T ₁ is connected to a power supply V _CC through a resistor R _2, also via the resistor R ₁ is connected to the base of the transistor T _2. The base of transistor T ₂ are, is connected to the positive pole of the constant voltage source DC ₁ in contact with the ground and the negative electrode. Connection between the collector of the emitter and the transistor T ₂ of the transistors T ₁ is grounded through the capacitor C _0. Connection of the transistors T ₁ and the resistor R ₀ is being directly connected to the base of the transistor T ₃ which is connected to the power supply V _CC to the collector, the emitter thereof is grounded through a resistor R _4.

[0005] The emitter of the transistor T ₃ is connected to one side voltage output terminal 1c, the other-side voltage output terminal 1d is grounded. In this phase shift circuit, the input voltage e _i
And the output voltage e ₀ is

[0006]

(Equation 1)

[0007] Here _{r e << | 1 / (ωC} 0) |
Then, equation (1) becomes

[0008]

(Equation 2)

## EQU1 ## Therefore, the output voltage e ₀ is shifted by 90 degrees from the input voltage e _i . Phase shifting circuit shown in Figure 3, one side voltage input terminal 1a is connected to the base of transistor T ₁₀ via a capacitor C _11. The base of transistor T ₁₀ is grounded through a resistor R _11, is connected to the power supply V _CC through a resistor R _12. The collector of the transistor T ₁₁ which is commonly connected transistor T ₁₀ and the emitter is connected to the power supply V _CC through a series circuit of the transistor T ₁₂ and the resistor R _3, the collector of the transistor T ₁₀ is directly connected to the power supply V _CC ing.

The emitters of the transistors T ₁₀ and T ₁₁ are grounded via a series circuit of a transistor T ₁₄ and a resistor R ₁₄ . Connection of the collector of the collector and the transistor T ₁₁ of the transistor T ₁₂ is directly to the power supply V collector
It is connected to the base of the transistor T ₁₃ which is connected to the _CC. The emitter of the transistor T ₁₃ is the resistance through the R ₁₀ is connected to the base of the transistor T _11, also is directly connected to one side voltage output terminal 1c, it is grounded via further resistor R _17.

[0011] The base of the transistor T ₁₁ is the capacitor C
Grounded via ₁₀ . The power supply V _CC is grounded via a resistor R ₆ , a transistor T ₁₆ , and a series circuit of a transistor T ₁₅ and a resistor R ₁₅ . The base of transistor T ₁₆ is connected to the base of the collector and the transistor T _12. The base of transistor T ₁₅ is commonly connected to the base of the transistor T _14, is connected to the positive electrode of the battery DC ₁₁ in contact with the ground and the negative electrode. In this phase shift circuit, the relationship between the input voltage e _i and the output voltage e ₀ is

[0012]

(Equation 3)

## EQU1 ## Where C ₀ is the capacitor C
The capacitance value of ₁₀ and R ₀ are the resistance values of the resistor R ₁₀ . And
When the equation (3) is modified and simplified in consideration of the fact that the open loop gain A is sufficiently large, the following equation is obtained: e ₀ = e _i (jωC ₀ R ₀ +1) (4) Then, in order to eliminate the real axis (+1), e _{0 in} equation (4) is used.
When e _i is subtracted from the _equation , e ₀ −e _i = jωC ₀ R ₀ (5), and the output voltage e ₀ is shifted by 90 degrees from the input voltage e _i .

[0014]

Incidentally, in the phase shift circuit shown in FIG. 1, since the amount of phase shift depends on the resistance R ₀ and the capacitor C ₀ , the amount of phase shift differs according to the characteristics thereof. . The order to be in a phase shifting circuit shown in FIG. 2 is negligible resistance value of r _e (emitter resistance varies according to the emitter current) differential resistance of transistors T ₁ is necessary to increase the collector current of the transistor T ₂ And power consumption increases.

Further, the phase shift amount does not become 90 degrees due to the influence of the capacitance between the collector and the base. Further, in the phase shift circuit shown in FIG. 3, the voltage obtained by subtracting the input voltage e _i from the output voltage e ₀ becomes jωC ₀ R ₀ as shown in equation (5), and the resistance R ₁₀ , the capacitor C ₁₀ , and the input voltage e _{Although the} phase shifts by 90 degrees irrespective of the frequency of _i , the absolute value | ωC ₀ R ₀ | changes according to the frequency of the input voltage e _i , and |
ωC ₀ R ₀ | increases.

[0016] Then, the phase-shifting circuit is easily affected by such stray capacitances of the transistors T ₁₁ and T ₁₃ constitute a negative feedback amplifier circuit, that is positively fed back to the frequency of the input voltage increases At that time, if the gain of the negative feedback amplifier circuit is 1 or more, oscillation may occur.

For this reason, phase shift circuits shown in FIGS. 4 and 5 have been proposed in which oscillation is not caused. Phase shifting circuit shown in Figure 4, connects the capacitor C _S to prevent oscillation between the collectors of the transistors T ₁₀ of the transistor T _11, the other components of the phase shift circuit shown in FIG. 3 And the same components are denoted by the same reference numerals. In this phase shift circuit, the open loop gain (transfer function) A of the negative feedback amplifier circuit is

[0018]

(Equation 4)

## EQU1 ## On the other hand, the phase shift circuit shown in FIG.
The base of the transistor T ₁₃ is grounded through a series circuit between the oscillation preventing capacitor C _S and a resistor R _S for preventing oscillation. The other configuration is the same as that of the phase shift circuit shown in FIG. 3, and the same components are denoted by the same reference numerals. In this phase shift circuit, the open loop gain A of the negative feedback amplifier is

[0020]

(Equation 5)

## EQU1 ## Therefore, as shown by the equations (6) and (7), the open loop gain A of the negative feedback amplifier circuit in the phase shift circuits shown in FIGS. 4 and 5 does not increase above a predetermined frequency, and the equation (4) holds. No longer. Therefore, when the frequency of the input voltage is equal to or higher than the predetermined frequency band, the phase shift amount deviates from 90 degrees. Also in order to obtain a voltage of 90 degrees phase-shifted from the input voltage e _i is the required circuit subtracting the input voltage e _i from the output voltage e _0, there is a problem that the phase characteristic of the circuit is greatly affected.

The present invention has been made in view of the above problems, and has as its object to provide a phase shift circuit capable of obtaining a phase shift amount of 90 degrees without causing phase shift and oscillation.

[0023]

A phase shift circuit according to the present invention comprises a differentially connected first and second transistors and an input signal.
Between the input terminal to be applied and the base of the first transistor
A resistor interposed in the
Capacitor between the output terminal and the second transformer
A DC constant voltage source connected to the base of the
The base of the transistor collector and the output terminal
Negative with a third transistor having its emitter connected
A feedback amplifier circuit, be connected to one collector of the first transistor to its collector, the fourth transistor is connected to its base to the output terminal via a resistor, the fourth
A DC negative feedback circuit including a fifth transistor differentially connected to the transistor, a capacitor interposed between the bases of the fourth and fifth transistors, and a resistor constituting a low-pass filter together with the capacitor and the resistor; It is characterized by having.

[0024]

Assuming that the input voltage of the negative feedback amplifier circuit is e _i and the output voltage is e ₀ , the relationship between e ₀ and e _i is

[0025]

(Equation 6)

Here, C ₀ is the condition of FIG.
The capacitance value of the capacitors C _30, R ₀ is Der same resistance value of the resistor R ₃₀
You. Simplifying this equation,

[0027]

(Equation 7)

## EQU1 ## If the open loop gain A is 1 << A,

[0029]

(Equation 8)

And the output voltage e e with respect to the input voltage e _i
0 shifts 90 degrees.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 6 is a block diagram showing the configuration of the phase shift circuit according to the present invention. Transistor T _31, which are differentially connected and the voltage input terminal 1a via a resistor R _30, the transistor T ₃₂ of the T ₃₂
Connected to the base. The voltage input terminal 1b is connected to the positive electrode of the constant voltage source DC ₃₂ whose negative electrode is grounded.
₃₉ through, is connected to the base of transistor T ₃₄ of the transistor T _33, T _34, which are differentially connected, is connected to the base of the transistor T ₃₁ via further resistor R _31.

The emitters of the transistors T ₃₁ and T ₃₂ are commonly connected, and are grounded via a series circuit of a transistor T ₃₈ and a resistor R ₃₄ . The collector of the transistor T ₃₁ is directly connected to the power supply V _CC, a collector of the transistor T ₃₂ is connected to the power supply V _CC through a series circuit of a transistor T ₃₆ and the resistor R _32. Connection between collectors of the transistors T ₃₆ of the transistor T ₃₂ is connected to the collector of the base and the transistor T ₃₃ of the transistor T _35.

The base of the transistor T ₃₆ is connected to the base and collector of the transistor T _37, the emitter of the transistor T ₃₇ is connected to the power supply V _CC through a resistor R _33. And these transistors T ₃₆ and T ₃₇ are connected in a current mirror. The collector of the transistor T ₃₇ is grounded through a series circuit of the transistors T ₄₀ and resistor R _36. The collector of the transistor T ₃₅ is directly connected to the power supply V _CC, and its emitter is grounded through a series circuit of the transistors T ₃₉ and resistor R _35.

The base of the transistor T ₃₂ is the capacitor C
It is connected to the base of the transistor T ₃₃ via a series circuit of ₃₀ and resistor R _38. Connection of the capacitor C ₃₀ and resistor R ₃₈ are connected to the voltage output terminal 1c. The voltage output terminal 1d is grounded. Between the bases of the transistor T ₃₄ of the transistor T ₃₃ is the capacitor C ₃₁ is interposed, their emitters is grounded via a series circuit of the transistors T ₄₁ and resistor R ₃₇ is connected to a common ing. The bases of the transistors T ₃₈ , T ₃₉ , T ₄₀ , and T ₄₁ are connected in common, and the negative electrode is grounded.
_It is connected to ₃₁ positive electrodes.

That is, this phase shift circuit comprises transistors T ₃₁ , T ₃₂ , T ₃₅ , T ₃₆ , T ₃₇ , T ₃₈ , T ₃₉ , T ₄₀ ,
A resistor R ₃₀ and a capacitor C ₃₀ constituting a low-pass filter
And an AC negative feedback amplifier circuit ANF surrounded by a broken line, and a resistor R constituting a low-pass filter.
₃₈ , R ₃₉ , capacitor C ₃₁ and transistors T ₃₃ , T ₃₄
DC negative feedback circuit section DNF surrounded by a broken line that feeds the DC voltage back to the negative feedback amplifier circuit section ANF.
Is provided.

The transistors T ₃₈ , T ₃₉ , T ₄₀ , T
₄₁ constitutes a constant current source, and the resistors R ₃₄ , R ₃₆ and R ₃₇ are selected to have the same resistance value. Therefore, transistors T ₃₈ , T ₄₀ ,
Equal collector current of T _41, when the current value of each and 2I _0, since the transistor T ₃₆ and T ₃₇ are connected in a current mirror, the resistance value of the resistor R _32, R ₃₃ is as long as the resistance value , the collector current of the transistor T ₃₆ becomes 2I _0.

Next, the AC operation of the phase shift circuit will be described. The base of the transistor T ₃₁ is grounded in terms of alternating current. Transistor T ₃₆ is, has a load for withdrawing an output from the transistor T _31, T ₃₂ of the differential connection with current, since the alternating current load becomes a very large value, the open loop gain A is sufficiently large. Transistor T ₃₂ the base current of the transistor T ₃₅ is changed when the collector current changes in, derived as a voltage output at the emitter follower transistor T _35. The output voltage e ₀ output from the emitter follower of the transistor T ₃₅ is supplied to a high pass filter capacitor C _30, resistor R _30. Input voltage is e
_{Assuming i} , the relationship with the output voltage e ₀ that has passed through the high-pass filter is

[0038]

(Equation 9)

## EQU1 ## The input voltage e _i is the base potential of the transistor T ₃₂ of the transistor T _31, T _32, which are differentially connected. The base potential of the transistor T _31, because they are AC-grounded, the relationship between the input voltage e _i and the output voltage e _0,

[0040]

(Equation 10)

In consideration of the fact that the open loop gain A is sufficiently large, the equation (12) becomes

[0042]

[Equation 11]

The phase shift amount becomes 90 degrees. In addition, the higher the frequency of the input voltage e _i, the lower the output voltage e ₀ , so that no oscillation occurs. Therefore, a resistor and a capacitor for preventing oscillation become unnecessary. Further, no phase shift occurs due to the characteristics of the circuit elements, and the phase shift amount does not deviate from 90 degrees.

Next, a DC operation will be described. Negative feedback amplifier circuit ANF but alternating manner are negatively fed back in the capacitor C ₃₀
As a result, no negative feedback is provided in terms of DC. Therefore emitter voltage of the transistor T _35, the negative feedback amplifier circuit remains the undefined does not operate. However, the transistor T
Only the DC component of the voltage output from the emitter follower ₃₅ is supplied to the low-pass filter of the resistors R ₃₈ and R ₃₉ and the capacitor C ₃₁ and the differentially connected transistors T ₃₃ and T ₃₄
Is supplied to the base of a transistor T ₃₃ of the transistor. The voltage of the constant voltage source DC ₃₂ is supplied to the base of the transistor T ₃₄ (ignoring the base current of the transistors T ₃₃ and T _{34 and} the voltage drop due to the resistors R ₃₈ and R ₃₉ ). shunt ratio of the collector current 2I ₀ of the transistor T ₄₁ is changed, the collector current of the transistor T ₃₃ is changed.

The DC voltage at the bases of the transistors T ₃₁ and T ₃₂ is maintained at the voltage of the constant voltage source DC ₃₂ (the voltage drop due to the base currents of the transistors T ₃₁ and T ₃₂ and the resistances R ₃₁ and R ₃₀ is ignored. ) The collector current flowing through the transistors T ₃₁ and T ₃₂ is I ₀ obtained by equally dividing the collector current 2I ₀ of the transistor T ₃₈ .

[0046] The collector current of the transistor T ₃₆ 2
If the base current of the transistor T ₃₅ is negligible small enough because it becomes I _0, the collector current of transistor T ₃₃ becomes I ₀ obtained by subtracting the collector current of the transistor T ₃₂ from the collector current of the transistor T _36.
And to the collector current of the transistor T ₃₃ of the differentially connected transistors T _33, T ₃₄ is I _0, since the collector current of the transistor T ₄₁ is 2I _0, the base voltage of the transistor T _33, T ₃₄ is must be equal, since the emitter of the DC voltage of the transistor T ₃₅ is fixed to the voltage of the constant voltage source DC _32, the negative feedback amplifier circuit ANF this voltage as the operating point to work properly.

[0047]

As described in detail above, according to the present invention, no phase shift occurs due to variations in the characteristics of circuit elements, and it is not necessary to prevent oscillation using a capacitor for preventing oscillation and a resistor for preventing oscillation. . Further, a high-precision phase shift circuit which can obtain a phase shift amount of 90 degrees can be provided without requiring a circuit for subtracting an input signal from an output signal . And before or after the input terminal
It is not necessary to have a large capacitor, so for example
There is no need to externally connect the capacitor, and the entire IC
The present invention has excellent effects, for example, it is possible to perform

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a conventional phase shift circuit.

FIG. 2 is another circuit diagram of a conventional phase shift circuit.

FIG. 3 is another circuit diagram of a conventional phase shift circuit.

FIG. 4 is a circuit diagram of a conventional phase shift circuit provided with an oscillation prevention circuit.

FIG. 5 is another circuit diagram of a conventional phase shift circuit including an oscillation prevention circuit.

FIG. 6 is a circuit diagram of a phase shift circuit according to the present invention.

[Explanation of symbols]

T ₃₁ through T ₄₁ transistors R ₃₀ to R ₃₉ resistors C _30, C ₃₁ capacitors DC _31, DC ₃₂ a constant voltage source ANF negative feedback amplifier circuit DNF negative feedback circuit

Claims (1)

(57) [Claims] 1. A differentially connected first and second transistor,
The input terminal to which the input signal is to be applied and the first transistor
A resistor interposed between the base and the base and the output signal
A capacitor interposed between the output terminal to be taken out,
A DC constant voltage source connected to the base of the second transistor,
And the base of the collector of the first transistor,
A third transistor whose emitter is connected to the output terminal
A negative feedback amplifier circuit comprising, be connected to one collector of the first transistor to its collector, a fourth transistor is connected to its base to the output terminal via a resistor, the fourth transistor and the differential connection A fifth transistor, a capacitor interposed between the bases of the fourth and fifth transistors, and a DC negative feedback circuit including a resistor constituting a low-pass filter together with the capacitor and the resistor. And the phase shift circuit.