JPH0448019Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Field of industrial application The present invention relates to a phase shift circuit suitable for use in a quadrature detection circuit of an FM stereo receiver. It is intended to provide a phase circuit.

(b) Prior Art A quadrature detection circuit used in the detection stage of an FM stereo receiver performs FM detection by multiplying an input signal by a 90-degree phase-shifted signal of the input signal. Therefore, in order to obtain the 90 degree phase shifted signal, a phase shift circuit is required, but the phase shift circuit changes the phase difference between the input signal and the output signal according to the frequency shift of the input signal. It must be configured as follows. The applicant had previously submitted
No. 59-30810 was filed regarding a phase shift circuit. In the above application, a series circuit of a resistor and a capacitor is inserted between the collectors of the first and second transistors that are differentially connected.
An input signal is applied between the bases of the second transistor and the second transistor, and an output signal is obtained from the connection point between the resistor and the capacitor. By using the phase shift circuit according to the above application, it is possible to obtain an output signal whose phase corresponds to the frequency shift of the input signal, and it is possible to obtain a phase shift circuit with a wide output dynamic range with an arbitrary gain.

(c) Problems to be solved by the invention However, the phase shift circuit according to the above application:
When converting into an IC, two terminal pins are required to externally attach a capacitor that forms a series circuit, which poses the problem of an increase in the number of pins, which is not desirable for an IC.

(d) Means for solving the problems The present invention has been made in view of the above-mentioned points. a resistor, a third resistor and a capacitor connected in series between the collector of the first transistor and ground, a signal obtained at a connection point between the first and second resistors, and a connection point between the third resistor and the capacitor; The present invention is characterized in that it is equipped with a subtraction circuit that performs subtraction with a signal obtained from the above.

(E) Effect According to the present invention, the first signal determined by the ratio of the first and second resistors is used as a reference, and the phase-shifted second signal is obtained at the connection point of the third resistor and the capacitor. Since the subtraction is performed, it is possible to obtain an output signal whose phase corresponds to the change in the input signal frequency.

(F) Embodiment Figure 1 shows an embodiment of the present invention. 1
5 and 6 are differential amplifier circuits consisting of first and second transistors 2 and 3 whose emitters are commonly connected, and a constant current source 4 connected to the common emitter; first and second resistors, 7 and 8, connected in series between the collectors;
is a third resistor and a capacitor connected in series between the collector of the first transistor 2 and the ground;
and 9 are differentially connected third and fourth transistors 10 and 11 and the third and fourth transistor 1.
0 and 11, and a constant current source 12 connected to the common emitters of the first and second resistors 5 and 6.
This is a subtraction circuit that subtracts the signal obtained at the connection point between the third resistor 7 and the capacitor 8 and the signal obtained at the connection point between the third resistor 7 and the capacitor 8.

Input signals applied to first and second input terminals 13 and 14 connected to the bases of first and second transistors 2 and 3, respectively, are amplified by the differential amplifier circuit 1 , and Output signals having mutually opposite phases are generated from the collectors of transistors 2 and 3. Thus, the voltage between the collectors of the first and second transistors 2 and 3 is divided by the first and second resistors 5 and 6, and applied to the base of the fourth transistor 11 of the subtraction circuit 9. The voltage obtained at the collector of one transistor 2 is
The voltage is divided by the resistor 7 and the capacitor 8 and applied to the base of the third transistor 10 of the subtraction circuit 9 . Therefore, in the subtraction circuit 9 , the voltage divided by the first and second resistors 5 and 6 is subtracted from the voltage divided by the third resistor 7 and capacitor 8, and the voltage divided by the first and second resistors 5 and 6 is subtracted. Output signals having mutually opposite phases are generated at the second output terminals 15 and 16.

Now, if the voltage obtained at the collector of the first transistor 2 is -V ₁ and the voltage obtained at the collector of the second transistor 3 is V ₁ , then the voltage obtained at the connection point of the first and second resistors 5 and 6 is V ₂ is V ₂ =−2R ₂ /R ₁ +R ₂ V ₁ (1) (where, R ₁ and R ₂ are the resistance values of the first and second resistors 5 and 6). Moreover, the voltage V ₃ obtained at the connection point of the third resistor 7 and the capacitor 8 is V ₃ = -1/jac/R ₃ +1/jacV ₁ ...(2) However, R ₃ is the resistance of the third resistor 7. The value C is the capacitance value of the capacitor 8, and ω is the angular frequency of the input signal. Therefore, the first output terminal 15 of the subtraction circuit 9
The output voltage V ₄ obtained is V ₄ =V ₂ −V ₃ =(1/1+jωR ₃ C−2R ₂ /R ₁ +R ₂ )V ₁ (3), and the second output of the subtraction circuit 9 The output voltage _V5 obtained at the terminal 16 is _V5 = _V3 - _V2 =( _2R2 / _R1 + _R2-1 /1+ _jωR3C ) _V1 ...(4). Therefore, for example, the phase angle between the output voltage V ₄ obtained at the first output terminal 15 and the voltage -V ₁ obtained at the collector of the first transistor 2 is: =tan ^-1 -ωR ₃ C(R ₁ +R ₂ )/R ₁ −R ₂ −2R ₂ (ωR ₃
C) ² ...(5). Therefore, the voltage V ₄ available at the first output terminal 15 will be phased only with respect to the voltage V ₁ available at the collector of the first transistor 2,
The phase angle depends on the angular frequency ω of the input signal.

Here, the relationship between the first and second resistors 5 and 6 is as follows:
If R ₁ =3R ₂ is set, the output voltage V ₄ shown by the above equation (3) becomes V ₄ =1−jωR ₃ C/2(1+jωR ₃ C)V ₁ ……(3)′, The phase angle expressed by the above equation (5) is as follows: =tan ⁻¹ −2ωR ₃ C/1−(ωR ₃ C) ² ……(5)′. By the way, when the output voltage V ₄ shown by the above-mentioned equation (3)' is expressed as a vector, it becomes as shown in FIG. 2.
As is clear from FIG. 2, the voltage V ₂ obtained at the connection point of the first and second resistors 5 and 6 becomes a vector with a magnitude of 1/2 V ₁ in the positive real axis direction. Further, the vector of the voltage V ₃ obtained at one end of the capacitor 8 moves on the dashed line according to the angular frequency ω of the input signal. And the vector of output voltage V ₄ is
The starting point is the tip of the vector with voltage V ₂ and the ending point is the tip of the vector with voltage V ₃ . Then, the voltage V ₃ obtained at one end of the capacitor 8
Since the vector of the voltage V 4 across the third resistor 7 becomes as shown in the figure, the vector of the voltage V ₄ across the third resistor 7 becomes as shown by the dotted line in FIG.
Therefore, when |V ₃ |=|V _A |, that is,
When 1/ωC=R ₃ , the vector of output voltage V ₄ is perpendicular to the vector of voltage V ₁ , and the phase angle is 90
degree. Therefore, if the phase shift circuit of FIG. 1 is used in a quadrature detection circuit, the phase difference between the input signal and the output signal will be 90 degrees when the frequency displacement of the input signal is zero, and if the frequency displacement of the input signal exists, It is possible to obtain a phase shift characteristic in which the phase difference changes from 90 degrees depending on the amount of displacement. Furthermore, the first
and the parallel resistance value of the second resistors 5 and 6 and the third resistor 7
If the values of are set equal, the voltage drops corresponding to the base currents of the third and fourth transistors 10 and 11 of the subtraction circuit 9 can be made equal. Therefore, the input offset of the subtraction circuit 9 can be prevented, and the accuracy of the operation can be improved.

When the capacitor 8 or coil shown in FIG. 1 is used as a reactance element, it may not be possible to obtain a sufficient amount of phase rotation because the reactance of the capacitor 8 or coil changes relatively gently with respect to frequency. On the other hand, ceramic resonators have a steep reactance change with respect to frequency, so a sufficient amount of phase rotation can be obtained at high frequencies. In addition, since the reactance change of the capacitor 8 and the coil is a function of the reciprocal of the frequency, the linearity of the phase rotation is poor and the distortion rate deteriorates, but in the case of a ceramic resonator, the linearity is good and the distortion rate is also good. It is. Therefore, if a ceramic resonator is used in place of the capacitor 8 as the reactance element in FIG. 1, the characteristics can be further improved.

One end of the capacitor 8 used as a reactance element is connected to the third resistor 7,
The other end of the capacitor 8 is grounded. Therefore, the differential amplifier circuit 1 , the first to third resistors 5 to 7
When integrating the capacitor 8 into a single IC and attaching the capacitor 8 externally to the IC, it is sufficient to arrange only one connection pin. Also, the circuit in Figure 1 is
A balanced input signal is applied to the bases of the first and second transistors 2 and 3 constituting the differential amplifier circuit 1 , and the connection point between the first and second resistors 5 and 6 and the base of the fourth transistor 11 is connected. Since the connection point between the third resistor 7 and capacitor 8 and the base of the third transistor 10 can be directly connected without using a coupling capacitor, unnecessary rotation of the phase can be prevented, making it more suitable for IC implementation. be.

(g) Effects of the invention As described above, according to the invention, a phase shift circuit that can obtain a phase shift amount corresponding to the frequency shift of an input signal can be obtained. Additionally, since the number of external pins and external components can be reduced, a phase shift circuit suitable for IC implementation can be obtained. Furthermore, if a ceramic resonator is used as the reactance element, a phase shift circuit with improved characteristics such as linearity and distortion rate can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a vector diagram for explaining the present invention. Explanation of main figure numbers, 1 ... Differential amplifier circuit, 5...
First resistor, 5... Second resistor, 7... Third resistor, 8
...Capacitor, 9 ...Subtraction circuit.

Claims (1)

[Claims for Utility Model Registration] (1) First and second transistors that are differentially connected, first and second impedance elements that are connected in series between the collectors of the first and second transistors, and the first and second transistors that are connected in series. a third impedance element and a reactance element connected in series between the collectors of one of the first and second transistors and the ground; a signal obtained at the midpoint of connection of the first and second impedance elements; and the third impedance element. and a subtraction circuit that performs subtraction with a signal obtained at the midpoint of the connection of the reactance element, and a signal obtained at the output terminal of the subtraction circuit according to the frequency of the input signal applied to the first and second transistors. A phase shift circuit characterized in that the phase of the phase shift circuit is changed. (2) By setting the ratio of the first and second impedance elements to 3:1, the input signal is transmitted at a frequency where the absolute value of the impedance of the third impedance element is equal to the absolute value of the reactance of the reactance element. 2. The phase shifting circuit according to claim 1, wherein the phase difference between the output signal and the output signal is 90 degrees.