JPH05226969A - Phase shift circuit - Google Patents

Abstract

PURPOSE:To shift a phase of an output signal by 90 deg. with respect to that of an input signal without causing a phase deviation and any oscillation. CONSTITUTION:A collector of a transistor(TR) T32 and a base of a TR T35 in an AC negative feedback amplifier circuit ANF are connected together and an emitter of the Tr T35 is connected to a base of the TR T32 via a capacitor C30 to input an input voltage e1 to the base of the TR T32 via a resistor R30. A DC voltage in response to the collector current of the Tr T32 is fed back negatively to the emitter of the Tr T35 by using a DC negative feedback circuit DNF to fix the emitter voltage of the TR T35.

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 is
For example, it is shown in JP-A-59-379. This kind of phase shift circuit is used for processing various signals. A conventional phase shift circuit of this type is constructed, for example, as shown in FIGS. 1, 2 and 3, respectively.

The phase shift circuit shown in FIG. 1 has a voltage input terminal 1
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 There is. 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 with 1d. This phase shift circuit includes resistors R _A 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
The phase difference with is 90 degrees.

In the phase shift circuit shown in FIG. 2, one side voltage input terminal 1a is connected to the base of the transistor T ₁ via a capacitor C ₁ and the other side voltage input terminal 1b is grounded.
The collector of the transistor T ₁ is connected to the power source V via the resistor R _0.
It is connected to _CC and its emitter is grounded through a series circuit of a transistor T ₂ and a resistor R ₃ . The base of the transistor T ₁ is connected to the power supply V _CC via the resistor R ₂ and also connected to the base of the transistor T ₂ via the resistor R ₁ . The base of the transistor T ₂ is connected to the positive electrode of the constant voltage source DC ₁ whose negative electrode is grounded. The connection between the emitter of the transistor T _{1 and} the collector of the transistor T ₂ is grounded via the capacitor C ₀ . The connection between the transistor T ₁ and the resistor R ₀ is connected to the base of the transistor T ₃ whose collector is directly connected to the power supply V _CC, and its emitter is grounded via the resistor R ₄ .

The emitter of the transistor T ₃ is connected to the one side voltage output terminal 1c, and 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

[0006]

[Equation 1]

[0007] Where r _e << | 1 / (ωC ₀ ) |
Then equation (1) becomes

[0008]

[Equation 2]

[0009] Therefore, the output voltage e ₀ is shifted by 90 degrees from the input voltage e _i . In the phase shift circuit shown in FIG. 3, the one-side voltage input terminal 1a is connected to the base of the transistor T ₁₀ via the capacitor C ₁₁ . The base of the transistor T ₁₀ is grounded via the resistor R ₁₁ and is connected to the power supply V _CC via the resistor R ₁₂ . The collector of the transistor T ₁₁ whose emitter is commonly connected to the transistor T ₁₀ is connected to the power supply V _CC through the series circuit of the transistor T ₁₂ and the resistor R ₃ , and 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 the series circuit of the transistor T ₁₄ and the resistor R ₁₄ . The connection between the collector of the transistor T _{12 and} the collector of the transistor T ₁₁ is such that the collector is directly connected to the power source V
_It is connected to the base of a transistor T ₁₃ which is connected to _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.

The base of the transistor T ₁₁ is the capacitor C.
Grounded through ₁₀ . The power supply V _CC is grounded through 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 the transistor T ₁₆ is connected to its collector and the base of the transistor T ₁₂ . The base of the transistor T ₁₅ is commonly connected to the base of the transistor T ₁₄ , and is connected to the positive electrode of the battery DC ₁₁ whose negative electrode is grounded. In this phase shift circuit, the relationship between the input voltage e _i and the output voltage e ₀ is

[0012]

[Equation 3]

[0013] Then, by modifying the equation (3) and simplifying it considering that the open loop gain A is sufficiently large, it becomes e ₀ = e _i (jωC ₀ R ₀ +1) (4). Then, in order to erase the real axis (+1), e _{0 of the} equation (4)
When e _i is subtracted from, e ₀ −e _i = jωC ₀ R ₀ (5), and the output voltage e ₀ is phase shifted by 90 degrees from the input voltage e _i .

[0014]

By the way, in the phase shift circuit shown in FIG. 1, the amount of phase shift depends on the resistor R ₀ and the capacitor C ₀ , so the amount of phase shift differs depending on their characteristics. .. 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 Therefore, power consumption increases.

Furthermore, the amount of phase shift does not reach 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 the equation (5), and the resistance R ₁₀ , the capacitor C ₁₀ , and the input voltage e _The phase shifts by 90 degrees regardless of the frequency of _i , but the absolute value | ωC ₀ R ₀ | changes depending on the frequency of the input voltage e _i , and if the frequency becomes high, |
ωC ₀ R ₀ | becomes large.

The phase shift circuit is easily affected by the stray capacitance of the transistors T ₁₁ and T ₁₃ forming the negative feedback amplifier circuit, and may be positively fed back when the frequency of the input voltage becomes high. If the gain of the negative feedback amplifier circuit is 1 or more at that time, oscillation may occur.

Therefore, the phase shift circuits shown in FIGS. 4 and 5 have been proposed in which oscillation is prevented. In the phase shift circuit shown in FIG. 4, an oscillation preventing capacitor C _S is connected between the collector of the transistor T _{11 and} the collector of the transistor T ₁₀ , and the other components are the phase shift circuit shown in FIG. The same reference numerals are given to the same components. In this phase shift circuit, the open loop gain (transfer function) A of the negative feedback amplifier circuit is

[0018]

[Equation 4]

It becomes On the other hand, the phase shift circuit shown in FIG.
The base of the transistor T ₁₃ is grounded via a series circuit of an oscillation prevention resistor R _S and an oscillation prevention capacitor C _S. The other configuration is the same as that of the phase shift circuit shown in FIG. 3, and the same components are designated by the same reference numerals. In this phase shift circuit, the open loop gain A of the negative feedback amplifier circuit is

[0020]

[Equation 5]

[0021] Therefore, as shown in Eqs. (6) and (7), the open loop gain A of the negative feedback amplifier circuit in the phase shift circuit shown in FIGS. 4 and 5 does not increase above a predetermined frequency, and Eq. (4) holds. Will not do. Therefore, when the frequency of the input voltage is equal to or higher than the predetermined frequency band, the amount of phase shift 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.

In view of the above problems, it is an object of the present invention to provide a phase shift circuit which can obtain a phase shift amount of 90 degrees without causing phase shift and oscillation.

[0023]

A phase shift circuit according to the present invention is a phase shift circuit for amplifying an input signal by a negative feedback amplification circuit to obtain an output signal which is phase shifted by 90 degrees. A capacitor interposed in a negative feedback loop, a resistor interposed in the circuit where the input signal should be input to the negative feedback loop, and a circuit that negatively feeds back a DC component of the output signal to a negative feedback amplifier circuit. It is characterized by including.

[0024]

When 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]

Simplifying this equation,

[0027]

[Equation 7]

[0028] If the open loop gain A is 1 << A,

[0029]

[Equation 8]

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

[0031]

The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. 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 with the base of. The voltage input terminal 1b is connected to the positive electrode of the constant voltage source DC ₃₂ whose negative electrode is grounded, and the resistor R
It is connected via ₃₉ to the base of the transistor T ₃₄ of the differentially connected transistors T ₃₃ and T ₃₄ , and further connected to the base of the transistor T ₃₁ via the resistor R ₃₁ .

The emitters of the transistors T ₃₁ and T ₃₂ are commonly connected and 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. The connection between the collector of the transistor T _{32 and} the collector of the transistor T ₃₆ is connected to the base of the transistor T ₃₅ and the collector of the transistor T ₃₃ .

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. These transistors T ₃₆ and T ₃₇ are current-mirror connected. The collector of the transistor T ₃₇ is grounded via the series circuit of the transistor T ₄₀ and the resistor R ₃₆ . The collector of the transistor T ₃₅ is directly connected to the power supply V _CC, and the emitter of the transistor T ₃₅ is grounded via the series circuit of the transistor T ₃₉ and the 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 through a series circuit of ₃₀ and the resistor R ₃₈ . The connection between the capacitor C ₃₀ and the resistor R ₃₈ is connected to the voltage output terminal 1c. The voltage output terminal 1d is grounded. A capacitor C ₃₁ is interposed between the base of the transistor T _{33 and} the base of the transistor T ₃₄ , and their emitters are commonly connected and grounded via a series circuit of a transistor T ₄₁ and a resistor R _37. ing. The bases of the transistors T ₃₈ , T ₃₉ , T ₄₀ , and T ₄₁ are commonly connected, and a constant voltage source DC whose negative electrode is grounded
_It is connected to ₃₁ positive electrodes.

That is, the phase shift circuit includes 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 that form a low-pass filter.
And the like, and includes an AC negative feedback amplifier circuit ANF surrounded by a broken line, and constitutes a resistor R that constitutes a low-pass filter.
₃₈ , R ₃₉ , capacitor C ₃₁ , and transistors T ₃₃ , T ₃₄
, Etc., the DC voltage is fed back to the negative feedback amplification circuit section ANF, and the DC negative feedback circuit section DNF surrounded by the broken line.
It is configured to include.

The transistors T ₃₈ , T ₃₉ , T ₄₀ , T
_Reference numeral ₄₁ constitutes a constant current source, and resistors R ₃₄ , R ₃₆ and R ₃₇ are selected to have the same resistance value. Therefore, the transistors T ₃₈ , T ₄₀ ,
If the collector currents of T ₄₁ are equal and the respective current values are 2I ₀ , since the transistors T ₃₆ and T ₃₇ are connected in a current mirror, the resistance values of the resistors R ₃₂ and R ₃₃ are the same. , The collector current of the transistor T ₃₆ becomes 2I ₀ .

Next, the AC operation of this phase shift circuit will be described. The base of the transistor T ₃₁ is AC-grounded. The transistor T ₃₆ serves as a load for extracting the output from the differentially connected transistors T ₃₁ and T ₃₂ with a current, and the AC load has a very large value. Therefore, 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 the high pass filter of the capacitor C ₃₀ and the resistor R ₃₀ . Input voltage e
The relation with the output voltage e ₀ passed through the high pass filter is _i

[0038]

[Equation 9]

It becomes The input voltage e _i becomes the base potential of the transistor T ₃₂ of the differentially connected transistors T ₃₁ and T ₃₂ . Since the base potential of the transistor T ₃₁ is AC-grounded, the relationship between the input voltage e _i and the output voltage e ₀ is

[0040]

[Equation 10]

Considering that the open loop gain A is sufficiently large, the equation (12) becomes

[0042]

[Equation 11]

And the amount of phase shift becomes 90 degrees. Further, the higher the frequency of the input voltage e _i, the smaller the output voltage e _0, so that oscillation does not occur. Therefore, the oscillation preventing resistor and capacitor are not required. Furthermore, the phase shift does not occur due to the characteristics of the circuit element, and the phase shift amount does not deviate from 90 degrees.

Next, a DC operation will be described. Negative feedback amplifier circuit ANF negatively feeds back AC, but capacitor C ₃₀
Therefore, DC is not negatively fed back. Therefore, the emitter voltage of the transistor T ₃₅ becomes indefinite and the negative feedback amplifier circuit does not operate as it is. But the transistor T
Only the DC component of the voltage output from the emitter follower of ₃₅ is supplied to the low pass filter of the resistors R ₃₈ and R ₃₉ and the capacitor C ₃₁ and differentially connected to the transistors T ₃₃ and T _34.
Is supplied to the base of the transistor T ₃₃ . The base of the transistor T ₃₄ is supplied with a voltage of the constant voltage source DC _32, by (ignoring the voltage drop due to the base current of the transistor T _33, T ₃₄ and the resistor R _38, R ₃₉₎ a difference between the base voltage The shunt ratio of the collector current 2I ₀ of the transistor T ₄₁ changes, and the collector current of the transistor T ₃₃ changes.

Since the DC voltage at the bases of the transistors T ₃₁ and T ₃₂ is held 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 resistors R ₃₁ and R ₃₀ is neglected). The collector current flowing through the transistors T ₃₁ and T ₃₂ is I ₀ , which is the collector current 2I ₀ of the transistor T ₃₈ divided equally.

The collector current of the transistor T ₃₆ is 2
Since the base current of the transistor T ₃₅ is sufficiently small and can be ignored because it is I ₀ , the collector current of the transistor T ₃₃ is I ₀ obtained by subtracting the collector current of the transistor T ₃₂ from the collector current of the transistor T ₃₆ .
Since the collector current of the transistor T ₃₃ of the differentially connected transistors T ₃₃ and T ₃₄ becomes I ₀ , since the collector current of the transistor T ₄₁ is 2I ₀ , the base voltage of the transistors T ₃₃ and T ₃₄ is Must be equal to each other and the DC voltage of the emitter of the transistor T ₃₅ is fixed to the voltage of the constant voltage source DC ₃₂ , so that the negative feedback amplifier circuit ANF operates normally with this voltage as the operating point.

[0047]

As described in detail above, according to the present invention, there is no phase shift due to variations in the characteristics of circuit elements, and there is no need to prevent oscillation by using an oscillation preventing capacitor or an oscillation preventing resistor. .. Further, it is possible to provide a highly accurate phase shift circuit that can obtain a phase shift amount of 90 degrees without requiring a circuit for subtracting an input signal from an output signal.

[Brief description of 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 including 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)

[Claims] 1. An input signal is amplified by a negative feedback amplifier circuit,
In a phase shift circuit for obtaining a phase-shifted output signal, a capacitor inserted in the negative feedback loop of the negative feedback amplifier circuit and an input signal input to the negative feedback loop are inserted in the middle of the circuit. A phase shift circuit comprising a resistor and a circuit for negatively feeding back a DC component of the output signal to a negative feedback amplifier circuit.