JPH06338767A - Voltage controlled oscillation circuit and voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To improve followup ability for the frequency fluctuation of a voltage controlled oscillation circuit. CONSTITUTION:The oscillation frequency(f) of a multivibrator type voltage controlled oscillation circuit provided with transistors 14, 15 of a feedback means, first and second transistors 12, 13, and a capacitor 11 varies by the charge/discharge time of the capacitor 11 and delay time generated in the feedback means. A first constant current source 20 which inputs a first control voltage V1 controls a current I relating to the charge/discharge time of the capacitor, and a second constant current source 30 which inputs a second control voltage V2 controls the delay time generated in the feedback means and the current I.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a PLL (Phase Locked).
Loop) Voltage controlled oscillator (hereinafter VC) used in frequency synthesizer system (hereinafter PLL system), etc.
O)).

[0002]

2. Description of the Related Art Conventionally, as a technique in such a field,
For example, some documents were described in the following documents. Reference: Japanese Patent Laid-Open No. 2-119309 SUMMARY OF THE INVENTION Conventionally, a so-called emitter-coupled multivibrator type voltage controlled oscillator circuit having a simple circuit configuration as a VCO and suitable for a monolithic integrated circuit has been widely used. FIG. 2 is a circuit diagram showing a configuration example of a conventional emitter-coupled multivibrator type voltage controlled oscillator circuit. Figure 2
Is a circuit that outputs a signal having an oscillation frequency according to a first control voltage provided from the outside, and includes a multivibrator 10 and a first constant current source 20. The multivibrator 10 connects the bases of the transistors 13 and 12 by connecting the collectors of the transistors 12 and 13 to the bases of the first and second transistors 12 and 13 whose emitters are coupled by the capacitor 11 of the first capacitive element. Transistors 14 and 1 as feedback means for supplying currents to the respective
5, the bases of the transistors 12 and 13 and the ground potential VE
And constant current sources 16 and 17 respectively connected to E. The collectors of the transistors 14 and 15 are connected to the power supply potential VCC and the transistors 14 and 1 are connected to each other.
The base of No. 5 is connected to the power supply potential Vcc via bias resistors 18 and 19, respectively. The constant current source 20 is
It has transistors 21 and 22 which commonly input the first control voltage V1. Each transistor 21,2
The collectors of 2 are connected to the electrodes of the capacitor C11, and the stabilizing resistors 23 and 24 are connected between the emitters of the transistors 21 and 22 and the ground potential VEE.

Next, the operation of the voltage controlled oscillator circuit of FIG. 2 will be described. When the transistor 12 is on and the transistor 13 is off, the current I flows through the resistor 18, the transistor 12,
It flows to VEE through the capacitor 11, the transistor 22, and the resistor 24. When the capacitor 11 is charged by the current I, the potential of the emitter of the transistor 13 decreases, and the transistor 13 is turned on and the transistor 12 is turned off. When the transistor 13 is on and the transistor 12 is off, the current I is in the opposite direction to
That is, the resistor 19, the transistor 13, the capacitor 11,
It flows to VEE through the transistor 21 and the resistor 23. The current I charges the capacitor 11 in the opposite direction. Along with that, the potential of the emitter of the transistor 12 is lowered, and the transistor 12 is turned on again and the transistor 13 is turned off again. After that, by repeating the same operation, the voltage controlled oscillator circuit oscillates. Here, the oscillation frequency f is the time for charging and discharging the capacitor 11, the transistors 14, 15 and the constant current source 16,
It is determined by the delay time of the feedback circuit consisting of 17.
In the case of FIG. 2, since the delay time of the feedback circuit is constant, the oscillation frequency f is determined by the charging / discharging time of the capacitor 11. The oscillation frequency f is proportional to the magnitude of the current I and inversely proportional to the capacitance C of the capacitor 11, as in the following equation. f = kI / C where k is a proportional constant The first control voltage V1 applied to the bases of the transistors 21 and 22 controls the current I to control the charging / discharging time of the capacitor 11, and the oscillation frequency f changes. To do.

[0004]

However, the conventional voltage controlled oscillator circuit has the following problems. (1) The control voltage for the oscillation frequency is one of the control voltages V1, and in a PLL system, for example, the control voltage V1 is controlled via a low-pass filter (hereinafter referred to as LPF) in order to stabilize the oscillation frequency. is doing. in this case,
Even if the frequency is slightly changed, it takes a long time to reach the desired frequency because of the time constant of the LPF.
If the time constant of the LPF is reduced to shorten the time, there is a problem that the oscillation frequency f is not stable. (2) The free-running oscillation frequency of the voltage controlled oscillator circuit is inversely proportional to the capacitance C of the capacitor 11. When the capacitance C of each product fluctuates due to manufacturing variations, the free-running oscillation frequency changes for each manufacturing lot. Therefore, there is a problem that the control voltage V1 must be offset-adjusted by a resistor or the like for each manufacturing lot. SUMMARY OF THE INVENTION The present invention provides a voltage-controlled oscillation circuit that solves the problems that the above-mentioned conventional techniques have with respect to the fact that it takes time to change the oscillation frequency and that the free-running frequency differs for each manufacturing lot.

[0005]

According to a first aspect of the present invention, in order to solve the above-mentioned problems, a voltage-controlled oscillation circuit includes first and second transistors whose emitters are connected to each other via a capacitor, and the above-mentioned first and second transistors. Feedback means for supplying base currents based on collector potentials of the first and second transistors to the bases of the second and first transistors, respectively;
A constant current source circuit connected between the emitter of the transistor and the ground potential and controlling the charging / discharging current of the capacitor based on a first control voltage, and an oscillation frequency according to the first control voltage. It is configured to output the signal of. Further, the voltage controlled oscillator circuit according to the present invention is provided with a second constant current source which is connected between the bases of the first and second transistors and the ground potential and which controls the base current based on a second control voltage. There is. According to a second invention, in the voltage controlled oscillator circuit according to the first invention, a third constant current source connected in parallel with the second constant current source for controlling the base current based on a third control voltage is provided. It is provided. According to a third aspect of the invention, in the voltage controlled oscillator, the first free running frequency is determined.
The voltage controlled oscillator circuit, which has the capacitive element and outputs the signal of the oscillation frequency according to the input first control voltage, is monolithically mounted on the semiconductor substrate. Here, a second capacitance element having the same structure as the first capacitance element formed on the substrate is provided, and a second capacitance element corresponding to the capacitance value of the second capacitance element is output based on the output of the voltage controlled oscillation circuit. A control circuit for generating a control voltage of 2 is provided. Then, the second control voltage is superimposed on the first control voltage and input to the voltage controlled oscillator circuit.

[0006]

According to the first aspect of the invention, since the voltage controlled oscillator circuit is configured as described above, the first and second transistors are
It operates complementarily by the feedback means. The capacitor is charged and discharged by the operation of the first and second transistors.
The charge / discharge of the capacitor changes the collector potentials of the first and second transistors, and the operation modes of the first and second transistors change. This change changes the direction of the charging / discharging current of the capacitor, causing the voltage controlled oscillator circuit to oscillate. The first control voltage controls the first constant current source to control the charging / discharging time of the capacitor. The second control voltage is
The second constant current source is controlled to control the delay time generated by the feedback means and the base currents of the first and second transistors. According to the second invention, the third control voltage controls the third constant current source. The third control voltage and the second control voltage in the first invention control the base currents of the first and second transistors. According to the third invention, since the voltage controlled oscillator circuit device is configured as described above, the first capacitive element and the second capacitive element are capacitive elements formed on the same substrate and having the same structure. . A second control voltage corresponding to the capacitance value of the second capacitive element is output from the control circuit, the second control voltage is superimposed on the first control voltage, and the second control voltage is input to the voltage controlled oscillator circuit. Therefore, the variation of the free-running frequency for each manufacturing lot determined by the capacitance value of the first capacitive element is suppressed. Therefore, the above problem can be solved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a circuit diagram showing a configuration example of a voltage controlled oscillator circuit according to a first embodiment of the invention. FIG. 1 shows an emitter-coupled multivibrator type voltage controlled oscillator circuit, which outputs a signal having an oscillation frequency controlled by a first control voltage V1 and a second control voltage V2. FIG. 1 includes a multivibrator 10, a first constant current source circuit 20 that inputs a control voltage V1 from the outside, and a second constant current source 30 that inputs a control voltage V2. The multivibrator 10 has a capacitor 1 whose emitters are the first capacitive element.
A first and a second transistor 12, coupled by 1
Have 13. The multivibrator 10 has transistors 14 and 15 as feedback means for connecting the collectors of the transistors 12 and 13 to the bases and supplying base currents to the transistors 13 and 12, respectively. The collectors of the transistors 14 and 15 are connected to the power supply potential VCC, and the bases of the transistors 14 and 15 are connected to the power supply potential VCC via the bias resistors 18 and 19, respectively.

The constant current source 20 has transistors 21 and 22 for inputting the first control voltage V1 to the bases from the input terminal T1. The collectors of the transistors 21 and 22 are connected to the electrodes of the capacitor C11, respectively, and the stabilizing resistors 23 and 24 are connected between the emitters of the transistors 21 and 22 and the ground potential VEE. The constant current source 30 is connected between the bases of the transistors 12 and 13 and the ground potential VEE, and inputs the control voltage V2 from the input terminal T2 to each base 31,
Has 32. The collectors of the transistors 31 and 32 are connected to the bases of the transistors 12 and 13, respectively, and the stabilizing resistors 33 and 34 are connected between the emitters of the transistors 31 and 32 and the ground potential VEE. FIG. 3 shows a VC including the voltage controlled oscillator circuit of this embodiment.
It is a block diagram of the PLL system using O. PL in Figure 3
The L system compares the frequencies of the input signal Si and the output signal So of the VCO and outputs a signal according to the phase difference to the LPF, and the output signal of the phase comparator 41 is a DC signal. LPF 42 for converting to the first control voltage V1
And a VCO 4 composed of the voltage controlled oscillator circuit of this embodiment.
3 and the frequency of the output signal So of the VCO 43 and the frequency of the input signal Si, and the second control voltage V2 corresponding to the phase difference
To the VCO.

Next, the operation of FIG. 1 will be described with reference to FIG. In FIG. 1, when the transistor 12 is on and the transistor 13 is off, the current I is the resistance 18, the transistor 12, the capacitor 11, the transistor 22, and the resistance 2.
4 to the ground potential VEE. When the capacitor 11 is charged by the current I, the potential of the emitter of the transistor 13 decreases, and the transistor 13 is turned on and the transistor 12 is turned off. When the transistor 13 is on and the transistor 12 is off, the current I is in the opposite direction, that is, the resistor 19, the transistor 13,
It flows to the ground potential VEE through the capacitor 11, the transistor 21, and the resistor 23. The current I charges the capacitor 11 in the opposite direction, and accordingly, the potential of the emitter of the transistor 12 decreases, and the transistor 12 returns to the on state and the transistor 13 returns to the off state. After that, by repeating the same operation, the voltage controlled oscillator circuit of FIG. 1 oscillates. The oscillation frequency f of the voltage controlled oscillator circuit is determined by the time for charging and discharging the capacitor 11 and the delay time of the feedback circuit including the transistors 14 and 15 and the constant current source 30.

A control voltage V1 generated by the LPF of FIG.
Controls the current I to control the charging / discharging time of the capacitor 11, and the oscillation frequency f changes. Second phase comparator 44
The second control voltage V2 generated by controls the delay time of the feedback circuit including the transistors 14 and 15 and the constant current source 30, and also controls the base currents of the transistors 11 and 12. As described above, in this embodiment, the constant current source 30 for inputting the second control voltage V2 in addition to the control voltage V1 for controlling the oscillation frequency is provided. Since the control voltage V2 controls the output frequency f of the VCO without passing through the LPF having a long time constant, the followability to the frequency change is improved especially in the high frequency region. Therefore, the oscillation frequency is stable, and a VCO suitable for the PLL system can be configured. In addition, since all of them are composed of elements that can be integrated, the circuit can be downsized. Second Embodiment The second embodiment is a voltage-controlled oscillator circuit of the first embodiment,
Further, a third constant current source 50 controlled by the third control voltage V3 is provided. FIG. 4 is a circuit diagram showing the second constant current source and the third constant current source in FIG. The constant current source 50 is connected in parallel with the second constant current source 30 between the bases of the transistors 12 and 13 and the ground potential VEE in FIG. 1, and inputs the control voltage V3 from the input terminal T3 to each base in common. It has transistors 51 and 52.
The collector of the transistors 51 and 52 is the transistor 1
Stabilizing resistors 53 and 54 are connected between the emitters of the transistors 51 and 52 and the ground potential VEE, respectively. The voltage controlled oscillator circuit equipped with the circuit of FIG. 4 oscillates similarly to FIG. 1, and the oscillation frequency f is controlled by the control voltages V1, V2 and V3. Here, for example, if the potential of the input terminal T3 is constant, that is, if the control voltage V3 is fixed to a constant potential, the control voltage V3
In combination with 2, it becomes possible to easily control the oscillation frequency of a digital signal.

Third Embodiment FIG. 5 is a block diagram showing an embodiment of the voltage controlled oscillator of the present invention. The circuit of FIG. 5 is a voltage controlled oscillator monolithically mounted on a semiconductor substrate, and has a first capacitive element built therein to output a signal So having an oscillation frequency corresponding to a first control voltage V4. The oscillator circuit 100 and a control circuit 110 which receives the output signal So thereof and outputs a second control voltage V5 corresponding to the capacitance value of the second capacitor element incorporated therein.
And the control voltages V4 and V5 are superposed on each other, and the voltage controlled oscillation circuit 1
00 for outputting to 00. Figure 6
FIG. 6 is a circuit diagram showing a configuration example of control circuit 110 in FIG. 5. The circuit of FIG. 6 includes a transistor 111 of an emitter follower for inputting a signal So to a base, and a capacitor 112 of a second capacitor element manufactured under the same conditions as the first capacitor element and connected to an emitter of the transistor 111. , And a resistor 113 for generating a delayed signal Sd, which is delayed together with the capacitor 112. The circuit of FIG. 6 further includes an amplifier configured by transistors 114 and 115, a load resistor 117, and a constant current source 116 for differentially amplifying the signal Sd, and an LPF 118.

Next, the operation of FIG. 5 will be described with reference to FIG. FIG. 7 shows a signal So input to the control circuit 110.
3 is a time chart of the signal Sd and the control voltage V5. The voltage controlled oscillator circuit 100 emits a free-running frequency depending on the capacitance value of the built-in first capacitive element. When the signal So of the free-running frequency is output, this signal So is delayed by the capacitor 112 and the resistor 113 of the control circuit 110 so that the fall time of the signal So is delayed.
It is said that Here, the delay time td of the signal Sd is determined by the time constant of the capacitor 112 and the resistor 113, and is a delay time proportional to the capacitance value C ₁ of the capacitor 112. Since the capacitor 112 has the same structure as the first capacitive element built in the voltage controlled oscillator circuit 100, if the capacitors 112 are manufactured at the same time, the capacitor 112 and
The capacitance value ratio of the capacitance element is substantially constant irrespective of the manufacturing lot, and can be expressed by the following equation, where C is the capacitance value of the first capacitance element. C ₁ = kC However, k is a proportional constant. Therefore, the signal V5 output from the LPF 118 via the differential amplifier is as shown in FIG. 7, and its DC component is
The value is in proportion to the delay time td, that is, in proportion to the capacitance value C ₁ . The broken line in FIG. 7 shows the signal level when the capacitance value C ₁ is small, and the solid line shows the signal level when the capacitance value C ₁ is large. FIG. 8 shows the output V6 of the superposition circuit 120.
When a diagram showing the relationship between the capacitance value C _1. Superimposing circuit 12
0 superimposes the control voltages V4 and V5 and outputs them to the voltage controlled oscillator circuit 100. That is, when the capacitance values C and C ₁ are large, the first control voltage of the voltage controlled oscillator circuit 100 also becomes large, and the oscillation frequency f is controlled to increase. As described above, in the present embodiment, it is possible to suppress the fluctuation of the free-running frequency due to the variation of the capacitance value C for each product, and it is not necessary to adjust each manufacturing lot by using the external resistance value.

Fourth Embodiment FIG. 9 shows a control circuit 130 used in place of the control circuit 110 in FIG. The control circuit 130 outputs the signal S
An inverter 131 for inputting o and a capacitor 132 of a second capacitance element manufactured under the same conditions as the first capacitance element and connected between the output terminal of the inverter 131 and the ground potential.
An inverter 133 serially connected to the output terminal of the inverter 131; an exclusive OR circuit 134 for inputting the output signal of the inverter 133 and the signal So;
And 35. Next, the control circuit 130 of FIG.
The operation of the voltage controlled oscillator used in the above will be described with reference to FIG. FIG. 10 is a diagram showing the levels of the signal So and the output signal A of the exclusive OR circuit 134.

Similarly to FIG. 5, when the signal So of the free-running frequency is output, the phase of the signal So is inverted by the inverter 131 of the control circuit 130. Inverter 13
The output pulse of 1 is delayed by the capacitor 132, and the inverter 133 inverts the phase of the signal. As a result, the pulse of the signal So is delayed and input to one input terminal of the exclusive OR circuit 134. The signal So is directly input to the other input terminal of the exclusive OR circuit 134, and the output signal V5 of the LPF is
As shown in FIG. 10, two pulses are output for one cycle of the pulse of the signal So. In FIG. 10, the broken line shows the signal level when the capacitance value C ₁ of the capacitor 132 is small, and the solid line shows the signal level when the capacitance value C ₁ is large. Therefore, even if the control circuit 130 of FIG. 9 is used instead of the control circuit 110 of FIG. 5, the capacitance values C, C ₁
Is high, the first control voltage of the voltage controlled oscillator circuit 100 is also high, and the oscillation frequency f is controlled to increase. As described above, in the present embodiment, it is possible to suppress the fluctuation of the free-running frequency due to the variation of the capacitance value C for each product, and it is not necessary to adjust the external resistance value for each manufacturing lot.

Fifth Embodiment FIG. 11 shows a control circuit 1 obtained by modifying the control circuit 130 shown in FIG.
At 40, an AND circuit 144 is provided instead of the exclusive OR circuit 134, and the control circuit 140 is used as a control circuit in the voltage controlled oscillator of FIG. Control circuit 140
Is an inverter 141 for inputting the signal So, a capacitor 142 of a second capacitance element manufactured under the same conditions as the first capacitance element and connected between the output terminal of the inverter 141 and the ground potential, and an output of the inverter 141. An inverter 143 connected in series to the terminal, an AND circuit 144 for receiving the output signal of the inverter 143 and the signal So, and an LP
It is composed of F145. The signal So is directly input to one input terminal of the AND circuit 144,
The delayed signal is applied to one input terminal of the circuit 144.
The structure is such that the polarity is inverted and input.

Next, the operation of the voltage controlled oscillator using the control circuit 140 of FIG. 11 will be described with reference to FIG. FIG. 12 is a diagram showing the levels of the signal So and the output signal B of the AND circuit 144. Similar to the fourth embodiment,
When the signal So of the free-running frequency is output, this signal So
Is delayed and input to one input terminal of the AND circuit 144. The signal So is directly input to the other input terminal of the AND circuit 144, and the output signal V5 of the LPF is
As shown in FIG. 12, one pulse is output for one cycle of the pulse of the signal So. In FIG. 12, the broken line shows the signal level when the capacitance value C ₁ of the capacitor 142 is small, and the solid line shows the signal level when the capacitance value C ₁ is large. Therefore, the control circuit 140 of FIG.
Even if it is used instead of the control circuit 110, the capacitance values C, C
_{When 1} is large, the first control voltage of the voltage controlled oscillator circuit 100 also becomes large, and the oscillation frequency f is controlled to increase. As described above, in the present embodiment, as in the third and fourth embodiments, it is possible to suppress the fluctuation of the free-running frequency due to the variation in the capacitance value C of each product, and to manufacture the external resistance value. No need to adjust for each lot.

The present invention is not limited to the above embodiment, and various modifications can be made. The following are examples of such modifications. (1) In the third to fifth embodiments, the control circuit 110,
Although the signals So are input to the input terminals 130 and 140, the same effect can be obtained even if the input signals are input via a frequency divider. (2) In the first and second embodiments, the transistors 12 and 13 forming the feedback means may be MOS transistors or the like. (3) In the second embodiment, the potential of the input terminal T3 is fixed to a constant value, but the same effect can be achieved by changing the input terminal T3 while keeping the potential of the input terminal T2 constant.

[0018]

As described above in detail, according to the first invention, in the voltage controlled oscillator circuit, the first control voltage controls the first constant current source, and the second control voltage is Control the second constant current source. The oscillation frequency is controlled by controlling the first and second constant current sources. Therefore, when used in a PLL system, for example, it is possible to obtain a voltage-controlled oscillation circuit having good followability with respect to a change in phase and a stable oscillation frequency. According to the second invention, the third constant current source controlled by the third control voltage is connected in parallel to the second constant current source of the first invention. For example, when the third control voltage is fixed and used at a constant potential, the oscillation frequency is controlled by the signal according to the second control voltage. Therefore, it is easy to control the oscillation frequency with a digital signal.
According to the third invention, the second capacitive element having the same structure as the first capacitive element that determines the free-running oscillation frequency is used to control the oscillation frequency of the first control voltage. Therefore, it is possible to suppress variations in the free-running oscillation frequency for each manufacturing lot, and it is possible to eliminate the need for an external adjustment terminal and make the apparatus compact or non-adjustable. First
According to the third invention, all the elements can be integrated, and the above effect can be realized without increasing the size of the circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a voltage controlled oscillator circuit according to a first embodiment.

FIG. 2 is a circuit diagram showing a conventional voltage controlled oscillator circuit.

FIG. 3 is a configuration diagram showing a PLL system using FIG.

FIG. 4 is a circuit diagram showing second and third constant current sources of a second embodiment.

FIG. 5 is a configuration diagram showing a voltage controlled oscillator according to a third embodiment.

6 is a circuit diagram showing a control circuit of FIG.

FIG. 7 is a time chart of FIG.

8 is a diagram showing a relationship between an output of the superimposing circuit of FIG. 6 and a capacitance value.

FIG. 9 is a circuit diagram showing a control circuit of a fourth embodiment.

FIG. 10 is a time chart of FIG.

FIG. 11 is a circuit diagram showing a control circuit of a fifth embodiment.

FIG. 12 is a time chart of FIG.

[Explanation of symbols]

11 Capacitor (First Capacitance Element) 12, 13 First and Second Transistors 13, 14 Feedback Means 20 First Constant Current Source 30 Second Constant Current Source 100 Voltage Controlled Oscillation Circuit 110, 130, 140 Control Circuit 112, 132, 142 capacitors (second capacitance elements) V1, V4 first control voltage V2, V5 second control voltage V3 third control voltage

Claims (3)

[Claims] 1. A first and a second transistor whose emitters are connected to each other through a capacitor, and a base current based on a collector potential of the first and the second transistor, and a base current of the second and the first transistor. And a first constant current source circuit that is connected between the emitters of the first and second transistors and the ground potential and that controls the charging / discharging current of the capacitor based on a first control voltage. A voltage-controlled oscillation circuit that outputs a signal having an oscillation frequency according to the first control voltage, wherein the voltage-controlled oscillation circuit is connected between the bases of the first and second transistors and a ground potential and is based on a second control voltage. A voltage controlled oscillator circuit comprising a second constant current source for controlling the base current. 2. The voltage controlled oscillator circuit according to claim 1, further comprising a third constant current source connected in parallel with the second constant current source and controlling the base current based on a third control voltage. A voltage controlled oscillator circuit characterized in that 3. A voltage controlled oscillator circuit, which has a first capacitive element whose free-running frequency is determined and which outputs a signal of an oscillation frequency according to an input first control voltage, is monolithically mounted on a semiconductor substrate. In the above voltage-controlled oscillation device, a second capacitance element having the same structure as the first capacitance element formed on the substrate is provided, and the second capacitance element of the second capacitance element is formed based on the output of the voltage-controlled oscillation circuit. A control circuit for generating a second control voltage according to a capacitance value is provided, and the second control voltage is superimposed on the first control voltage and input to the voltage controlled oscillation circuit. Voltage controlled oscillator.