JPH0520004B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a phase shift circuit suitable for integrated circuits, and particularly to a phase shift circuit that rotates only the phase by 360 degrees without changing the gain much with respect to the input frequency. It is related to phase circuits.

[Conventional technology]

The one shown in FIG. 3 has conventionally been used as this type of phase shift circuit. In the figure, 1
1 is an input terminal, 21 is a coupling capacitor, 22, 2
3 is a bias resistor, 31 is an NPN transistor, 32, 33, and 34 are resistors, 35 is a coil, 3
6 is a capacitor, 80 is a series resonant circuit consisting of a coil 35 and a capacitor 36, 25 is an NPN type emitter follower transistor, 24 is an emitter resistor, 12 is an output terminal, and 13 is a power supply terminal.

FIG. 4 shows an example of frequency characteristics of gain and phase of this circuit.

This circuit can obtain the characteristics shown in FIG. 4 with a simple circuit configuration and a small number of parts.
The circuit operation is as follows. That is, since the impedance of the series resonant circuit 80 increases as it moves away from the resonant frequency, the transistors 31 and 2
5 both operate as emitsuta followers. Therefore, the input signal is output with a gain of approximately "1" and a phase of 0°. At the resonant frequency, the series resonant circuit 8
The impedance of 0 becomes small, and the input signal becomes
The signal is inverted and amplified by the transistor 31 with a gain equal to the ratio of the resistors 32 and 33, and is output through the emitter follower transistor 25 via the series resonant circuit 80. Therefore, the output signal near the resonance frequency has a phase inverted by 180°. Note that the gain at this frequency can be freely set by changing the values of the resistors 32, 33, and 34.

[Problem that the invention seeks to solve]

However, when making this circuit into an integrated circuit, current technology cannot incorporate an LC resonant circuit.
At least two terminals in addition to the input/output terminals are required. Furthermore, since it is a grounded emitter amplifier circuit, there is also the drawback that ripples in the power supply voltage are output as they are.

This invention was made in order to solve the problems of the conventional circuits as described above, and is suitable for integrated circuits with a small number of terminals and a circuit that has little gain change over a wide band and rotates only the phase by 360°. Moreover, it is an object of the present invention to obtain a phase shift circuit that can be made resistant to power supply voltage ripples.

[Means for solving problems]

The phase shift circuit according to the present invention includes a first differential amplifier circuit to which a signal to be phased is differentially input, a second differential amplifier circuit to which a differential output of the circuit is input, and a first differential amplifier circuit to which a differential output of the circuit is input. a third differential amplifier circuit that shares a load resistance and receives one output of the first differential amplifier circuit directly and via a resistor, and has a gain approximately four times that of the second differential amplifier circuit; It is provided with an amplifier circuit and a series resonant circuit connected between a connection point between the circuit and the resistor and ground.

[Effect]

In this invention, when non-resonance, the differential inputs of the third differential amplifier circuit are the same input, and when resonant, one of the differential inputs of the third differential amplifier circuit is grounded, and the output of the circuit is Since one end of the series resonant circuit, which has a phase opposite to that of the output of the differential amplifier circuit 2, is grounded, only one external terminal is required for the series resonant circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a phase shift circuit according to an embodiment of the present invention, in which 10 and 11 are differential input terminals;
2 is an output terminal, and 13 is a power supply terminal. Also, transistors 51, 52 and resistors 61, 62, 63, 6
4 and the current source 41 constitute a first differential amplifier circuit 71. The transistors 53 and 54 constitute first and second emitter follower circuits 74 and 75 together with current sources 42 and 43, respectively. transistor 5
5 and 56 are emitter resistances 65 and 66, load resistance 6
9. A second differential amplifier circuit 72 is configured together with the current source 44. The transistors 57 and 58 constitute a third differential amplifier circuit 73 together with emitter resistors 67 and 68, a load resistor 69, and a current source 45. Here, the resistor 69 is a common load resistance of the second differential amplifier circuit and the third differential amplifier circuit.

Note that the resistors 65, 66, 67, 68 and the current sources 44, 45 are used so that the differential gain of the third differential amplifier circuit is approximately four times that of the second differential amplifier circuit.
Select the value of . In addition, 2 of the first differential amplifier circuit
resistors 61 and 6 so that the amplitudes of the two outputs are equal.
Let 2 be the same value.

In addition, in this embodiment, the coil 35 and the capacitor 36
The series resonant circuit 80 is connected between the connection point of the resistor 38 and the base of the transistor of the differential amplifier circuit 73 and the ground, and the output signal is sent to the output terminal via the emitter follower circuit consisting of the transistor 59 and the current source 46. 12.

The operation of this circuit is as follows. Input terminal 1
When a differential input signal is applied between 0 and 11,
Amplified outputs having opposite phases to each other are obtained at the collectors of the transistors 51 and 52. When the frequency of the input signal is sufficiently distant from the resonant frequency of the series resonant circuit 80, the same signal is applied to the input of the third differential amplifier circuit 73, and the differential input becomes zero. On the other hand, the differential output of the first differential amplifier circuit 71 is applied to the input of the second differential amplifier circuit 72 as a differential input through emitter follower circuits 74 and 75. Therefore, the output of the second differential amplifier circuit 72 is obtained at the load resistor 69, and this signal is emitter-followed and transmitted to the output terminal 12.

Next, consider a case where the frequency of the input signal is equal to the resonant frequency of the series resonant circuit 80. In this case, the impedance of the resonant circuit becomes approximately zero, and the base of transistor 58 becomes approximately direct current. Therefore, the output of the first differential amplifier circuit 71 is applied to the third differential amplifier circuit 73 as one side input. Since the output of the first differential amplifier circuit 71 is applied to the second differential amplifier circuit 72 as a differential input, the load resistance 6
9, the sum of the outputs of the second differential amplifier circuit 72 and the third differential amplifier circuit 73 is obtained. At this time, the second
The output of the differential amplifier circuit 72 is the output of the transistor 53
The third differential amplifier circuit 7 is in reverse phase when viewed from the emitter of
The outputs of 3 are in phase and cancel each other out. Here, the third differential amplifier circuit 73 is set to have a gain of about 4 times the differential input compared to the second differential amplifier circuit 72, and as described above, the third differential amplifier circuit 73 is a differential input, and the third differential amplifier circuit 73 is a one-sided input, so the output amplitude of the third differential amplifier circuit 73 is approximately twice that of the second differential amplifier circuit 72. Become. Therefore, the combined output signal obtained at the load resistor 69 has an opposite phase and approximately the same amplitude as the output signal at a non-resonant frequency.

This characteristic is shown in a graph as shown in FIG.

In this way, according to this example, a circuit is obtained in which the gain does not change much over a wide area and only the phase changes by 360 degrees, but in this example, one end of the series resonant circuit is grounded, and the Therefore, only one terminal is required for externally connecting the circuit, and a structure suitable for integration into an integrated circuit can be obtained. In addition, although two input terminals are shown in FIG. 1, and it appears that the number of input terminals is increased compared to the conventional example, the input terminals are not shown because the illustration of the preceding stage circuit of this phase shift circuit in the integrated circuit is omitted. This is only shown for convenience, and therefore, there is no increase in the number of input terminals due to the circuit configuration of this embodiment.

Furthermore, since the phase shift circuit of this embodiment is composed of only a differential amplifier circuit, ripples in the power supply voltage become the in-phase input of the differential amplifier circuit and do not appear in the output.

In the above embodiment, the ratio of the differential gains of the second differential amplifier circuit and the third differential amplifier circuit is selected to be 1:4, and the frequency characteristics of the gain are almost flat as shown in FIG. We obtained a characteristic in which the phase changes depending on the frequency, but the amplitude hardly changes. However, if the amplitude is made larger than 1:4, the amplitude becomes large at the resonant frequency, and conversely, when it is made smaller than 1:4, the amplitude becomes large at the resonance frequency. The amplitude decreases in frequency. In this way, the characteristics can be changed by selecting the gain ratio.

Further, in this embodiment, the series resonant circuit includes only a coil and a capacitor, but the series resonant circuit may be a series circuit of a resistor, a coil, and a capacitor. In this case, the impedance of the series circuit at the resonant frequency increases, so the transistor 58
A signal amplitude is generated at the base of the resistor 38 and the voltage divided by this impedance. Since this signal is in phase with the base signal of the transistor 57, this is equivalent to lowering the gain of the third differential amplifier circuit 73.

Further, in this embodiment, the base of the transistor 58 is directly connected to the resistor 38 and the series resonant circuit 80, but due to manufacturing variations etc.
If the hFE of 8 is low, a third emitter follower circuit 76 consisting of a third transistor 151 and a current source 47 may be inserted between them as shown in FIG. In this case, the emitter follower transistors 152, 153, the current source 49,
48 first and second level shift circuits 7
7 and 78 to correct the change in bias voltage caused by inserting an emitter follower between the transistor 58 and the series resonant circuit 80. Note that the level shift circuits 77 and 78 may be constructed of diodes 161 and 162 as shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, since the circuit configuration is such that one end of the series resonant circuit in which the differential inputs of the third differential circuit are the same or one side input is grounded, the number of terminals is It is possible to realize a phase shift circuit that is suitable for integrated circuit integration and is resistant to ripples in the power supply voltage.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a phase shift circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a characteristic example of an embodiment of the present invention, FIG. 3 is a diagram showing a conventional phase shift circuit, and FIG. 4 is a diagram showing a conventional phase shift circuit. This figure shows the characteristics of a conventional circuit, and FIGS. 5 and 6 show other embodiments of the present invention. In the figure, 51 is the first transistor, 52
is the second transistor, 53 is the third transistor, 54 is the fourth transistor, 55 is the fifth transistor, 56 is the sixth transistor, 57 is the seventh transistor, 58 is the eighth transistor, 61 is the a first resistor; 62 is a second resistor;
38 is the third resistor, 69 is the fourth resistor, 35
is the first coil, 36 is the first capacitor, and 42 is the first
, 43 is a second current source, 71 to 73 are first to third differential amplifier circuits, 74 to 76 are first to third emitter follower circuits, 80 is a series resonant circuit, 77 and 78 are The first and second level shift circuits 161 and 162 are diodes. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A first differential amplifier circuit in which each differential transistor has a load resistance and a signal to be phase shifted is input between two differential inputs; the first, where the output is input;
a second emitter follower circuit; a second differential amplifier circuit having only one differential transistor having a load resistance and into which the outputs of both emitter follower circuits are input; and a second differential amplifier circuit having a gain approximately four times that of the differential amplifier circuit; One differential input is connected directly to the output of the first emitter follower circuit through a resistor, and one differential transistor shares the load resistance with the second differential amplifier circuit. and a series resonant circuit connected between a connection point between the resistor and the third differential amplifier circuit and ground, A phase shift circuit characterized in that an output is taken out from a connection point between one differential transistor of the differential amplifier circuit and the load resistor. 2. The phase shift circuit according to claim 1, wherein the series resonant circuit comprises a coil and a capacitor. 3. The phase shift circuit according to claim 1, wherein the series resonant circuit comprises a resistor, a coil, and a capacitor. 4 The connection point between the above resistor and the series resonant circuit and the above third
A third emitter follower circuit is inserted between the outputs of the first and second emitter follower circuits and the differential input of the second differential amplifier circuit. Claims 1 to 3 are characterized in that first and second level shift circuits are inserted between them for correcting bias voltage changes caused by insertion of the third emitter follower circuit. The phase shift circuit described in either.