JPS6142899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide an oscillation circuit suitable for integration into an IC (integrated circuit). An oscillation circuit used in a local oscillation circuit or the like of a radio receiver must be able to obtain a plurality of oscillation frequencies and must operate stably at each oscillation frequency. Furthermore, the tuner section of a radio receiver has recently been increasingly integrated into an IC, and it is desired that the local oscillation circuit and the radio frequency amplification circuit and mixing circuit be formed on the same IC substrate. The present invention has been made in view of the above points, and will be described below based on embodiments with reference to the drawings. Figure 1 shows the basic system of the present invention.
1 is an in-phase amplifier that can obtain an output signal that is in phase with the input signal, 2 is an anti-phase amplifier that can obtain an output signal that is in opposite phase to the input signal, and 3 is a feedback circuit.
The input terminals and output terminals of the in-phase amplifier 1 and the anti-phase amplifier 2 are commonly connected, and the commonly connected output terminal is connected to the input terminal of the feedback circuit 3, and the commonly connected input terminal is connected to the feedback circuit. It is connected to the output terminal of 3. The feedback circuit 3 functions as a positive feedback circuit for the in-phase amplifier 1 and as a negative feedback circuit for the anti-phase amplifier 2. Then, the gain of the in-phase amplifier 1 is G ₁ and the gain of the anti-phase amplifier 2 is G 1 .
If the gain of is G ₂ and the feedback rate of the feedback circuit 3 is β, the oscillation circuit is in a stable state when (G ₁ −G ₂ )β=1 (1). According to the configuration shown in FIG. 1, the gain G ₁ of the in-phase amplifier 1 and the gain of the anti-phase amplifier 2 are
Since they can be changed externally independently or in conjunction with each other to a large extent, changes in the feedback factor β of the feedback circuit 3 caused by the operation of varying the output oscillation frequency are sufficiently compensated for, and a stable oscillation state is always maintained. You can. FIG . 2 shows a specific example of the basic system shown in FIG. In the differential amplifier circuit, 7 is a third circuit of the same conductivity type with a pair of emitters connected in common.
and a second differential amplifier circuit consisting of fourth transistors 8 and 9; 10 is a first constant current circuit connected to the common emitter of the first differential amplifier circuit 4 ; 11 is a first constant current circuit of the second differential amplifier circuit 7; A second constant current circuit connected to a common emitter, the bases of the first and third transistors 5 and 8, and the second and fourth transistors 6
The bases of transistors 5 and 9, the collectors of first and fourth transistors 5 and 9, and the collectors of second and third transistors 6 and 8 are commonly connected to each other. Thus, the first differential amplifier circuit 4 operates as the in-phase amplifier 1 of FIG. 1, and the second differential amplifier circuit 7 operates as the anti-phase amplifier 2 of FIG. Now, a positive signal is applied to the bases of the first and third transistors 5 and 8, and a positive signal is applied to the bases of the first and third transistors 5 and 8.
If a negative signal is applied to the bases of transistors 5 and 9, negative signals will be generated at the collectors of the first and third transistors 5 and 8, and positive signals will be generated at the collectors of the second and fourth transistors 6 and 9. As shown in equation (1), in order for the circuit of FIG. 2 to operate as an oscillation circuit, the condition G ₁ >G ₂ is required. Therefore, the current I ₁ flowing through the first constant current circuit 10 is set to be larger than the current I ₂ flowing through the second constant current circuit 11 (I ₁ >I ₂ ). Therefore, a positive signal is obtained at the common collectors of the second and third transistors 6 and 8, and a negative signal having the same absolute value as the positive signal is obtained at the common collectors of the first and fourth transistors 5 and 9. . The positive signal and the negative signal are respectively applied to the positive and negative input terminals of the feedback circuit 3, and the output signal of the feedback circuit 3 is applied to the first and second differential amplifier circuits 4 and 7 with the same polarity. As a result, a feedback loop is formed and the whole operates as an oscillation circuit. Therefore, the stabilization condition shown in equation (1) is satisfied by adjusting the current flowing through the first or second constant current circuit 10 or 11. The adjustment may be performed manually while looking at the measuring device, or may be performed using an ALC (automatic level control) circuit, which will be described later. As shown in Figure 2, using a differential amplifier allows the gains of both amplifier circuits to be changed in opposite directions at the same time, making gain adjustment easy and achieving a stable state. It is possible to provide an oscillation circuit that is stable and easy to integrate into an IC. FIG. 3 shows another embodiment of the present invention,
12 and 13 are first and second transistors serving as in-phase amplifiers, 14 and 15 are third and fourth transistors serving as anti-phase amplifiers, and 16 is a feedback circuit.
LC tuning circuit; 17 is a constant voltage circuit consisting of a transistor 18, a constant current circuit 19, a diode 20 and a Zener diode 21; 22 is a first input circuit consisting of a transistor 23, a diode 24 and a resistor 25; 26 is a transistor 27 and a diode a second input circuit, 30, consisting of 28 and a resistor 29;
whose collectors are connected to the first and second transistors 12
and a first control transistor 33 connected to the common emitters of and 13, the base of which is connected to the first input circuit 22 via transistors 31 and 32;
The collector is connected to the third and fourth transistors 14.
and a second control transistor 36, 37 and 38 connected to the common emitter of the level detection transistor 35 and whose base is connected to the emitter of the level detection transistor 35 via the transistor 34, biasing the first and second control transistors 30 and 33. and first, second, and third bias resistors that provide an offset therebetween. Therefore, the input signal to the first input circuit 22 is
Supplied from the constant voltage circuit 17 , the second input circuit 26
An input signal to the LC tuning circuit 16 is supplied to the base of a transistor 27 via a diode 28 from one end of the LC tuning circuit 16. Now, if we take the signal supplied to the base of the transistor 27 as a reference and make it a positive signal, a positive signal will be applied to the collectors of the first and third transistors 12 and 14, and a positive signal will be applied to the collectors of the second and fourth transistors 13 and 15. A negative signal is obtained at the collector of , the collectors of the first and fourth transistors 12 and 15 are commonly connected, and the collector signal of the first transistor 12 has a larger absolute value, so it becomes a positive feedback circuit. A positive signal is applied to one end of the LC tuning circuit 16. The gains of the first to fourth transistors 12 to 15 are the same as those of the first and second control transistors 30 and 33.
It changes by adjusting the current flowing through the
In the embodiment shown in FIG. 3, ALC
Since a circuit is provided, the gain can be automatically adjusted. That is, the second input circuit
The output signal from 26 is applied to the base of the level detection transistor 35 via the first resistor 36 and subjected to level detection, and then applied to the base of the second control transistor 33 via the transistor 34. On the other hand, the constant voltage from the first input circuit 22 is applied as a constant voltage bias to the base of the first control transistor 30 via the transistors 32 and 31. Now, if the power is turned on at a certain point, the base voltage of the first control transistor 30 will be at a predetermined value.
V ₁ , and the collector current of a predetermined value I ₁ is
The current flows to the control transistor 30. On the other hand, when the power is turned on, a voltage of a predetermined value _{V 2 is} also applied to the base of the second control transistor 33 . The voltage is divided by the first resistor 36 and the second resistor 37, and V ₁ >V ₂ . For that reason,
The collector current _I2 of the second control transistor 33 is also _I1
＞I ₂ or I ₂ 〓0, and in the initial state,
The gain G ₁ of the in-phase amplifier consisting of the first and second transistors 12 and 13 is always the same as the gain G 1 of the anti-phase amplifier consisting of the third and fourth transistors 14 and 15.
It is set so that it is much larger than G ₂ or G ₂ = 0. Then, a difference signal between the in-phase amplifier and the anti-phase amplifier is applied to the input terminal of the LC tuning circuit 16, which serves as a feedback circuit, and the difference signal between the in-phase and anti-phase amplifiers is transmitted through the feedback circuit and the second input circuit 26 . Since it is fed back to the phase amplifier, level detected and applied to the second control transistor 33, oscillation is started and the collector currents of the first and second control transistors 30 and 33 are
I ₁ and I ₂ are controlled so that I ₁ decreases and I ₂ increases, and the state satisfies the above-mentioned formula (1) and becomes stable. When using the oscillation circuit shown in FIG. 3 as a local oscillation circuit of a radio receiver, the LC tuning circuit 16
By making variable, an oscillation output of a desired frequency can be obtained. When the LC tuning circuit 16 is varied,
The amount of feedback, that is, β in equation (1) changes. Then, since the oscillation output changes, the second input circuit 26
The signal level applied to the second control transistor 33 via the level detection transistor 35 also changes, and the signal level applied to the second control transistor 33 from the first and second control transistors 30 and 3 changes.
The collector currents I ₁ and I ₂ of No. 3 also change to a state that satisfies the above-mentioned formula (1), and the oscillation circuit becomes stable again.
This is ALC operation, and by adding the ALC circuit, the oscillation circuit automatically becomes stable for all oscillation frequencies within a predetermined range. The change in output at this time can be kept small by increasing the ALC loop gain. By using the oscillation circuit shown in FIG. 3, stable oscillation output can be obtained with simple control. Further, since changes in the state of the feedback circuit can be sufficiently absorbed, there is an advantage that the degree of freedom in designing the feedback circuit increases and that various feedback circuits can be used. Furthermore, the oscillation circuit in Fig. 3 is
Since it has a balanced structure and can eliminate adverse effects caused by element changes, it is suitable for integrated circuits. As described above, the oscillation circuit according to the present invention is excellent with many advantages, and is highly effective when used in circuits that obtain oscillation outputs of a plurality of different frequencies, such as local oscillation circuits of radio receivers. It is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic system of the invention, FIG. 2 is a circuit diagram showing one embodiment of the invention, and FIG. 3 is a circuit diagram showing another embodiment of the invention. Explanation of main figure numbers: 1... In-phase amplifier, 2... Negative-phase amplifier, 3... Feedback circuit, 30, 33... Control transistor.

Claims (1)

[Claims] 1 A first amplifier circuit in which the input signal and output signal are in phase, and a second amplifier circuit in which the input signal and output signal are in opposite phase.
It consists of an amplifier circuit, a feedback circuit, and a gain control circuit that controls the gains of the first and second amplifier circuits,
The input terminals and output terminals of the first amplifier circuit and the second amplifier circuit are commonly connected, and the commonly connected output terminal is connected to the input terminal of the feedback circuit, and the commonly connected input terminal is connected to the input terminal of the feedback circuit. The gain amplifier circuit is connected to an output terminal of a feedback circuit, and the gain amplifier circuit is driven in accordance with an oscillation output signal obtained at the commonly connected output terminal, thereby controlling the gains of the first and second amplifier circuits. An oscillator circuit characterized in that a stable oscillation output is obtained.