JPH08274592A - Voltage-controlled oscillator circuit - Google Patents

Abstract

PURPOSE: To improve stability of oscillation by using plural differential amplifiers positioned mutually to be a front one and a rear one and connecting their differential input terminals and output terminals in a manner that they are opposite in operating characteristic to each other. CONSTITUTION: The differential input terminals 2, 3 and the differential output terminals 4, 5 located before and behind are connected in series and also in a ring shape by using the plural differential amplifiers so as to display their operating polarities opposite to each other. Currents corresponding to the input voltage of the terminals 2, 3 flow on differential input transistors 9, 10, and the sum of them flows on a current control transistor. In such a case, a constant DC current flows on a transistor 7 when it performs a constant current operation in a saturated area by a DC voltage supplied to the control input of a current control terminal 6. Therefore, the voltage of the drain terminal 8 of the transistor 7 is stabilized at a nearly constant voltage value without changing in a pulse shape steeply. Since a high oscillation frequency is obtained with a low voltage, low power consumption is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator circuit.

[0002]

2. Description of the Related Art A conventional voltage controlled oscillator circuit is shown in FIG.
As shown in FIG. 3, the inverting circuit is configured as a ring oscillator, and one current control transistor is inserted on each of the VDD side and the VSS side of one inverting circuit, and a control voltage input to the control input terminal 11 is used. The oscillation frequency is controlled by simultaneously controlling the currents flowing through the two current control transistors.

[0003]

The operating current of each inverting circuit in the conventional voltage controlled oscillator circuit is a function of the input voltage of the inverting circuit and is not constant. This is also clear from the operating principle of the CMOS inversion circuit. Therefore, the current flowing through the current control transistors 21 and 22 during the oscillating operation is also not constant, and the through current flowing through the inverting circuit flows in a pulse shape at a frequency twice the oscillation frequency. Therefore, the current control transistors 21 and 22 are required to operate in the constant current saturation region only at the moment when the pulse current flows, and are in the non-saturation region operation state at other times.

Looking at the drain terminals 23 and 24 of 21 and 22, the voltage of these terminals is also pulsed at a frequency twice as high as the oscillation frequency for the above reason. When the desired oscillation frequency is comparatively low, there is no particular problem, but when the oscillation is attempted at a higher frequency, the following new problem occurs.

In order to increase the oscillation frequency with the same control voltage, it is sufficient to increase the current capability of the current control transistors 21 and 22 to increase the operating current, but this usually requires an increase in the physical size of the transistors. Accordingly, the parasitic capacitances at 23 and 24 are increased in proportion to this. As described above, the voltages of 23 and 24 are swung at a frequency twice as high as the oscillation frequency. Therefore, if the parasitic capacitance is large, the high-speed voltage change is hindered and the parasitic capacitance acts to lower the oscillation frequency. From the above, even if the current capability of the current control transistor is increased in an attempt to increase the oscillation frequency, the oscillation frequency is limited to a low level by the parasitic capacitance, and the current flowing in the parasitic capacitance causes the operating current of the inverting circuit to increase. There was a problem that the linearity of the oscillation frequency was also impaired.

Further, in the conventional voltage-controlled oscillator circuit, four transistors are connected in series between the power supplies, so that the power supply voltage cannot be made lower than a certain voltage value in order to secure the terminal voltage of each transistor. There is a problem, and it is not possible to sufficiently cope with the recent reduction in power supply voltage. Further, as described above, since there are two current control transistors per inversion circuit, 20 control voltage conversion circuits are separately required, which has the following problems.

Control input 11 of a conventional voltage controlled oscillator circuit
When an AC signal is input to the current control transistor 22, it is transmitted to the gate terminal of the current control transistor 22 as it is, but it is transmitted to the gate terminal of the current control transistor 21 after passing through the control voltage conversion circuit 20. There will be a time lag. Further, even if 11 is driven with a sufficiently low impedance, the output impedance of the control voltage conversion circuit 20 cannot be made too small in terms of current consumption, so that the output of the control voltage conversion circuit 20 is easily affected by the oscillator, and There is a problem that it is difficult to increase the stability of the oscillating frequency.

Further, as described above, since a pulse-like through current flows at a frequency twice as high as the oscillation frequency in each inverting circuit, noise is superimposed on the power source unless the impedance of the power source is made sufficiently low to raise the oscillation frequency. Then, the problem that power supply noise affects other circuits or itself and the stability of oscillation is easily impaired occurs.

[0009]

A differential voltage input terminal and a pair of differential voltage output terminals are provided, and a result of amplifying a differential voltage input between the differential voltage input terminals is used as the differential signal. A differential amplifier that differentially outputs between output terminals, the differential amplifier including a differential amplifier in which an operating current of the differential amplification is controlled by an input of a control input terminal. It is characterized in that the differential voltage input terminal and the differential output terminal of the differential amplifier, which are arranged before and after each other, are connected in series and in a ring shape so that their operation polarities are opposite to each other. Further, the current control input terminals of the differential amplifier are connected to each other to be used as an input, and any output terminal of the differential amplifier is used as an output.

[0010]

FIG. 1 shows an embodiment of the voltage controlled oscillator circuit of the present invention using three differential amplifiers. FIG. 2 shows an example in which a differential amplifier 1 is composed of CMOS transistors. 2 and 3 are differential input terminals, and 4 and 5 are differential output terminals. A current control input terminal 6 controls the operating current of the operational amplifier by the voltage input to this terminal. Since the operation of this differential amplifier is well known, its explanation is omitted.

In the voltage controlled oscillator circuit of FIG. 1, the differential voltage input terminals and the differential output terminals of the differential amplifiers, which are arranged in front of each other, are connected in series and in a ring shape so that their operating polarities are opposite to each other. The dynamic amplifier is connected to form a ring oscillator. Further, the current control input terminals of the three differential amplifiers are connected to each other to form the control input terminal 11 of the voltage controlled oscillator circuit. Reference numeral 12 is an output terminal of the voltage controlled oscillator circuit. It should be noted that the output terminal may be any output terminal of any differential amplifier that constitutes the voltage controlled oscillator circuit,
Further, in FIG. 1, one of the differential amplifier output terminals is used for single-ended output, but both of the differential output terminals of the differential amplifier may be used for differential output. Moreover, the outputs of the plurality of differential amplifiers may be simultaneously used as the plurality of output terminals.

The operation state of the differential amplifier 1 in the oscillation state of the voltage controlled oscillator circuit of the present invention will be described below.
The differential input terminals 9 are provided for the differential input transistors 9 and 10.
The current corresponding to the input voltage of 3 and 3 flows, but the sum of both currents flows to the current control transistor of 7. Assuming that the current control transistor 7 has a constant current operation in the saturation region by the DC voltage applied to the control input 6, the current control transistor 7 has a constant DC current. Therefore, the voltage of the drain terminal 8 of the current control transistor 7 does not change sharply like a pulse as in the conventional voltage control type oscillation circuit, and is stabilized at a substantially constant voltage value. It is easy to optimize the configuration of the differential amplifier 1 and the control input voltage range 6 so that only the saturation region operation of the current control transistor 7 is used, because the voltage 8 is almost constant.

Since the voltage of 8 is almost constant, it is not necessary to charge and discharge the parasitic capacitance at the terminal 8 at high speed.
The influence of the parasitic capacitance is reduced. As a result, the oscillation frequency with respect to the operating current flowing through the current control transistor 7 is increased and the linearity is improved. Furthermore, since the operating current of the entire voltage controlled oscillator circuit is also a nearly constant DC current, the noise superimposed on the power supply is reduced, the stability of the oscillation frequency is improved, and the effect of noise from other power sources is reduced. can do.

Since the number of transistors connected in series between the power supplies is smaller than that in the conventional voltage controlled oscillator circuit, the power supply voltage can be reduced accordingly.
Even if the power supply voltage is reduced, high-frequency oscillation is possible because the influence of parasitic capacitance is small as described above.

Further, unlike the conventional voltage control type oscillation circuit, a control voltage conversion circuit is not required and only one control input terminal is required. Therefore, by driving the terminal with low impedance, voltage control with high frequency stability is achieved. Type oscillator circuit can be easily realized, and the time lag of the control voltage does not occur unlike the above-mentioned conventional voltage control type oscillator circuit. Therefore, the rate of change of the oscillation frequency with respect to the time change of the voltage input to the 11 control input terminals is also increased, and the dynamic characteristics are improved.

The embodiment described above is one embodiment of the voltage controlled oscillator circuit of the present invention. Although the differential amplifier 1 is composed of CMOS transistors in this embodiment, it may be composed of bipolar transistors. Further, although the loads of the differential input transistors 9 and 10 are composed of transistors, they may be composed of simple resistance elements.

[0017]

As described above, according to the voltage controlled oscillator circuit of the present invention, it is possible to operate at a lower power supply voltage and to obtain a high frequency oscillation frequency at a lower power supply voltage, as compared with the prior art. Effective in reducing power consumption. Further, the operation of the entire voltage controlled oscillator circuit is close to the direct current operation, so that the stability of the oscillation frequency is improved and the influence of noise through the power source on other circuits can be significantly reduced. Furthermore, since there is only one frequency control input terminal, the control voltage conversion circuit is not required, and the circuit is simplified and the dynamic characteristics are improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a voltage controlled oscillator circuit of the present invention.

FIG. 2 is a diagram showing a configuration example of a differential amplifier.

FIG. 3 is a diagram showing an example of a conventional voltage controlled oscillator circuit.

[Explanation of symbols]

 1 differential amplifier 2,3 differential input terminal 4,5 differential output terminal 6 current control input terminal 7 current control transistor 8 7 drain terminal 9,10 differential input transistor 11 control input terminal 12 voltage control type oscillation circuit Output terminal 20 Control voltage conversion circuit 21, 22 Current control transistor 23 21 drain terminal 24 22 drain terminal

Claims (2)

[Claims] 1. A pair of differential voltage input terminals and a pair of differential voltage output terminals are provided, and a result obtained by amplifying a differential voltage input between the differential voltage input terminals is provided between the differential output terminals. A differential amplifier that outputs differentially, the differential amplifier including a differential amplifier in which an operating current of the differential amplification is controlled by an input of a control input terminal. A voltage-controlled oscillation circuit in which the differential voltage input terminal and the differential output terminal of the differential amplifier are connected in series and in a ring shape so that their operation polarities are opposite to each other. 2. The voltage controlled oscillator circuit according to claim 1, wherein the current control input terminals of the differential amplifier are connected to each other,
A voltage-controlled oscillation circuit, wherein the control input terminal is used as an input and any one or a plurality of output terminals of the differential amplifier are used as an output.