JPH0936736A - Voltage controller oscillator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a stable circuit with less drift by taking the symmetry of each circuit into account thereby canceling fluctuation in characteristics with each other in the design of an integrated circuit. SOLUTION: When a free run frequency of a voltage controlled oscillator 104 changes, a voltage applied to a terminal 112 is changed automatically to keep an oscillating frequency of the circuit 104 to be a frequency fref of an oscillation circuit 107. When an optional voltage is given to a terminal 111 of a 2nd signal synthesis means 103, a voltage at a terminal 112 is adjusted so that the oscillating frequency of the circuit 104 is the fref . Thus, when the reference voltage at the terminal 112 is given to a 1st signal synthesis means 101, the oscillating frequency of the 1st voltage controlled oscillator 102 becomes fref by arranging characteristics of the means 101, 103 and the circuit 104. When the frequency fref set to be a desired free run frequency fc and the voltage applied to the means 101 is the reference voltage, the oscillating frequency of the circuit 102 is fc and then the circuit for the free run frequency ffc is realized.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a phase locked loop (P
The present invention relates to a voltage controlled oscillator circuit used for LL, Phase Locked Loop, etc. The present invention relates to a voltage-controlled oscillator circuit, particularly to a circuit in which the free-run frequency is stabilized.

[0002]

2. Description of the Related Art A large number of voltage-controlled oscillator circuits have been published. FIG. 3 shows, as an example, a voltage controlled oscillator circuit used in a one-chip complementary MOS integrated circuit for PLL (CMOS IC). N-channel transistor N ₁
The control voltage applied to the gate of control the current flowing into the capacitor C ₁ to control the oscillation frequency.
The resistors R ₁ and R ₂ determine the control voltage sensitivity coefficient and the free-run frequency, respectively.

As another example, FIG. 4 shows Japanese Patent Publication No. 56-8.
6509 shows a known voltage controlled oscillator circuit. This circuit controls the oscillation frequency by controlling the current flowing into the ring oscillator by the gate voltage of the transistors T _{41 to} T ₄₆ connected to the sources. Compared with the circuit of FIG. 4, this circuit does not require external parts and has the advantages of low power consumption and small mounting space, but it is difficult to make an accurate and stable oscillation circuit.

Further, the circuit of FIG. 3 cannot be said to have sufficient stability.

[0005]

Generally, for a voltage controlled oscillator circuit, it is the free run frequency and the voltage controlled sensitivity coefficient that are required to have stability. The former is the oscillation frequency when the voltage (control voltage) applied to the control terminal of the voltage controlled oscillator circuit is at the reference level. The reference level is usually selected at the center of the controllable input voltage range, for example, 1/2 of the power supply voltage in a CMOS IC, and the control voltage is V _C and the reference level voltage is V _S , and ΔV _C is If it is defined as ΔV _C = V _C −V _S (1), the free-run frequency may be restated as the oscillation frequency when ΔV _C = 0. The voltage control sensitivity coefficient K _V is defined as f ₀ = f _C + K _V · ΔV (2) f _C is the free run frequency, and f ₀ is the oscillation frequency of the voltage controlled oscillator circuit.

The drift of the free-run frequency f _C is a PLL
In, the adverse effect appears as a drift of the capture range of the system. Also, the variation in f _C due to the variation in the circuit component constant is so large that it cannot be ignored. Conventionally, high precision components should be used after preparing for high cost, or after assembly, adjustment and adjustment with a semi-fixed resistor or semi-fixed capacitor. Had to do. When the PLL is constructed, the drift of the voltage control sensitivity coefficient K _V becomes a drift of the response speed of the system and has an adverse effect.

The causes of these drifts are changes in the ambient temperature, fluctuations in the power supply used, changes in the component constants at light times, etc. In particular, the fluctuation of f _C is greatly drifted due to these factors. On the other hand, K _V can be determined by the relative accuracy of the components of the circuit, and its variation can be reduced by providing a relatively sufficient racking characteristic even though there is no absolute accuracy of the element value by semiconductor integrated circuit technology or the like. it can.

The present invention relates to a circuit system that suppresses the drift of a conventional voltage controlled oscillator circuit, and the oscillator circuit constant (f _C ,
The purpose is to reduce the fluctuation of K _V ) and increase the stability of the circuit.

Another object of the present invention is to provide a voltage controlled oscillator circuit which can be easily integrated into an integrated circuit by suppressing the fluctuation of the circuit constant with respect to the absolute accuracy.

[0010]

A voltage-controlled oscillator circuit according to the present invention has a first voltage-controlled oscillator whose oscillation frequency is controlled by a first synthesized signal and a characteristic equivalent to that of the first voltage-controlled oscillator. A second voltage-controlled oscillator having an oscillation frequency controlled by the second combined signal; and a phase-locked loop having a comparison circuit for comparing the phase of the output of the voltage-controlled oscillation circuit with the phase of the reference signal. An oscillating circuit, which is a first signal adding circuit for converting a first control signal and a second control signal output from the comparison circuit into currents and adding the currents to output the first combined signal. And a second signal adder circuit for converting the second control signal and the reference voltage into currents, adding the currents, and outputting the second combined signal.

[0011]

1 is a diagram showing the concept of the present invention. Reference numerals 101 and 103 denote signal synthesizing means designed to have the same characteristics. For example, a signal given to the terminal 109 (hereinafter, referred to as a voltage value. The same applies to other physical quantities such as a current value and a charge value. .) To V ₁₁ , terminal 110
V ₂₁ a signal voltage applied to, when the voltage appearing at the output terminal 114 of the signal combining means 101 and _{V 01 V 01 = f (V} 11, V 21) ····· (3) f is such as arbitrary function It is a circuit having characteristics. Hereinafter, for the sake of simplicity, it is assumed that V ₀₁ = aV ₁₁ + bV ₂₁ + C ... (4). (A, b, C are constants) Similarly, the voltages applied to the terminals 111 and 112 are V ₁₂ and V ₂₂ , respectively, and the output terminal 11 of the signal synthesizing means 103.
When the voltage of 5 is V ₀₂ , V ₀₂ = aV ₁₂ + bV ₂₂ +10 C ... (5). Reference numerals 102 and 104 denote voltage controlled oscillator circuits having uniform characteristics, and the output signal frequencies F ₁ and F ₂ are F ₁ = K _V V ₀₁ + d (6) F ₂ = K _V V ₀₂ + D ... (7) (d is a constant). Reference numeral 107 denotes a phase comparison circuit, which compares the output of the voltage controlled oscillation circuit 104 with the output signal of an oscillation circuit (for example, a crystal oscillation circuit) that oscillates at a stable frequency, and outputs a signal of an amount compared with the phase difference. Reference numeral 105 is a low-pass filter (LPF), which is normally inserted in order to extract only a desired signal component from the output of the phase comparison circuit.

The output of the LPF 105 is negatively fed back to the second input terminal 112 of the second signal synthesis circuit 103. That is, the second voltage controlled oscillator circuit 104, the phase comparison circuit 106,
The LPF 105 and the signal generating means 103 constitute a PLL, and the oscillation frequency of the second voltage controlled oscillation circuit becomes equal to the oscillation frequency fref of the oscillation circuit 107. Voltage controlled oscillator circuit 1
The output frequency of 04 is the phase comparison circuit 106 and the LPF 105.
It is possible to make fref and the phase completely coincide with each other by the characteristic of, and it is also possible not to follow a sudden change of fref. Since the oscillator circuit 107 normally uses a circuit that oscillates sufficiently stably, there is no problem even if the response of the system is fast. Further, the output frequency of the voltage controlled oscillator circuit 104 and fref follow only the frequency, and there may be an error in the phase, so there is considerable freedom in the configuration of the circuit.
When the oscillator circuit 107 is unstable and has a jitter or the like, its influence can be reduced by design.

Now, let us consider a case where the free-run frequency of the voltage controlled oscillator circuit 104 fluctuates due to fluctuations in the power supply voltage, temperature characteristics, changes over time, and the like. At this time, the system automatically raises and lowers the voltage applied to the terminal 112 to change the voltage controlled oscillation circuit 1
The oscillation frequency of 04 keeps fref. Further, even if an arbitrary voltage value is given to the first control terminal 111 of the second signal synthesizing means 103, the oscillation frequency of the second voltage controlled oscillator circuit becomes fref regardless of the voltage value. The voltage is adjusted automatically.

Therefore, when the reference voltage Vs is applied to the first input terminal 111 of the second signal synthesizing circuit, the second input terminal 112 is automatically level-adjusted and the oscillation frequency of the voltage controlled oscillator circuit 104 is adjusted. will be equal to fref. As shown in FIG. 1, the second input terminal 112 of the second signal combining means 103.
To the second input terminal 1 of the first signal combining means 101.
10, the characteristics of the first and second signal synthesizing means and the voltage controlled oscillator circuit are the same, so that the oscillation frequency of the first voltage controlled oscillator circuit 102 is the same as that of the first signal synthesizing means 101. The voltage applied to the input terminal 109 is V _S
In case of, it becomes fref. If fref is set equal to the desired free-run frequency f _C , the oscillation frequency of the voltage controlled oscillator circuit 102 is f _C when the voltage at the terminal 109 is V _S.
Becomes Therefore, if the entire circuit of FIG. 1 is a voltage controlled oscillator circuit having the terminal 109 as a control terminal and the terminal 113 as an output terminal, a voltage control circuit having a free-run frequency f _C can be realized. Two signal combining means 101, 10 in the circuit
3. The discussion has been made on the assumption that the voltage-controlled oscillator circuits 102 and 104 have the same characteristics, but this assumption is extremely valid. In particular, in the case of forming a monolithic integrated circuit, each can be built on a chip of several millimeters square with high accuracy and good symmetry. Since each circuit is manufactured at the same time, even if there is a change over time, the same elapsed time is maintained and the sustainability is unlikely to differ from one another. Further, the same power source is used for the power supply voltage and the temperature change, and since they are arranged at extremely close places, it is unlikely that a temperature difference occurs between them and the characteristics are different. If the symmetry of each circuit is taken into consideration when designing the integrated circuit, the fluctuations of the respective characteristics cancel each other out and a stable voltage controlled oscillator circuit with less drift can be realized.

FIG. 2 is a diagram showing a specific example of a voltage controlled oscillator circuit which can be realized by a semiconductor integrated circuit based on the above idea of the present invention. Reference numeral 201 denotes a signal synthesizing circuit, which changes the drain current of each of the transistor transistors T ₁ and T ₂ by changing the gate voltage thereof. The drain currents of T ₁ and T ₂ are included (added) and flow into the transistor T ₁₃ to be converted into a voltage. This voltage is the control voltage of the first voltage controlled oscillator circuit, and is input to the voltage controlled oscillator circuit 202 composed of a MOS transistor. This circuit Bok transistor _{T 7, T 10, T 8} , T 11, ··· T 9, constitute a ring oscillator by an odd number of stages of the inverter constituted by the T _12, the source further transistor T ₄ of each transistor, _{T 5 ··· T 6, T 15} , T 16 put · · · T ₁₇ in series, controlling the oscillation frequency by controlling the current flowing from the power supply to the ring oscillator by controlling a gate potential of the transistor of this such To do. In the example of the present invention, the lower the potential of the terminals 212 and 214, the higher the drain voltage of T ₁₃ (the control voltage of the voltage controlled oscillator circuit 202) and the higher the oscillation frequency. That is, this is the case where a and b are negative in the equation (4) and K _V is positive in the equation (6). Terminal 21
If it is desired to oscillate at a high frequency when the level of 2,214 is high, for example, the polarities of the transistors of the circuits 201 and 202 are all reversed (P channel transistor is N channel, N channel transistor is P channel). , A, b are negative and K _V is negative, which can be achieved. 205,
206 is a buffer circuit for obtaining an output.

Reference numerals 203 and 204 denote 201 and 202, respectively.
The signal synthesizing circuit and the voltage controlled oscillating circuit have the same circuit configuration. Since the internal structure is the same, the inside is omitted in the figure. The output of the second voltage controlled oscillator circuit is the puffer 207.
Is input to the phase comparison circuit 208 through. Reference numeral 211 is a crystal oscillation circuit, which is a frequency fre which is a reference of the free-run frequency.
This is an oscillation circuit that oscillates f (= f _C ). Normally, this signal is input to the phase comparison circuit 208 to be phase-compared with the output of the second voltage controlled oscillation circuit 204, and is also used as a timing clock or system clock for other circuits. If the frequency of the clock signal required by another circuit is different from the desired f _{C, the} node 219 or 218
It is possible to set f _C to an integral multiple of the oscillation frequency of the crystal oscillator circuit 211, an integer fraction, a difference between them, or an integer fraction adjustment by inserting a frequency dividing circuit or a frequency converting circuit in either one or both. It is possible. The frequency dividing circuit and the frequency converting circuit can be configured by digital circuits, and no trouble occurs when the semiconductor integrated circuit is formed. 217 is a low-pass filter, which is a phase comparison circuit 20.
The high frequency component included in the output of 8 is removed. Output is second
Is fed back to the second input terminal 215 of the signal combining circuit 203. The first input terminal 213 is connected to resistors R ₁₁ and R ₁₂ that divide the power supply voltage to give an input signal level (reference level) for oscillating f _C. It is difficult to make an accurate resistor in the semiconductor integrated circuit, but the relative accuracy can be made very high. A more accurate voltage source such as a reference voltage by a Zener diode may be connected to this terminal. Signals are taken out from different points inside the low-pass filter 217 and connected to the second input terminals 214 and 215 of the signal combining circuit for the first and second signals, but the resistor R ₄ stabilizes the PLL system. The resistance required for this purpose is not essentially different from the case of FIG.

Looking at the configuration of FIG. 2, all are MOS except resistors R _{11 to} R ₁₅ , capacitors C _{11 to} C ₁₃ , and a crystal oscillator X.
It is composed of a land transistor. Absolute accuracy is not required for resistors and capacitors. Therefore, the resistor can be built in the semiconductor integrated circuit. Also, although it depends on the required oscillation frequency range, the capacitor C ₁₁ can often be incorporated. Output terminal 21 when low frequency is required
By connecting the frequency divider circuit to 6, the PLL system can be made to oscillate at a high frequency so that C ₁ can have a small capacity and an integrated circuit can be easily formed.

As described above, according to the present invention, an extremely stable voltage controlled oscillator circuit can be realized without using high precision parts. Since it is not necessary to use high-precision parts, it is extremely easy to make a semiconductor integrated circuit, and mounting and manufacturing have a great deal of merit.

Comparing the example according to the present invention (FIGS. 1 and 2) with the conventional example (FIGS. 3 and 4), the present invention is considerably complicated, and it seems that there is no merit compared with the conventional example. May be done. However, the fact is the opposite, and when the circuit of FIG. 2 is formed on the semiconductor integrated circuit, the area occupied on the chip is small. When external components are required as in the conventional example of FIG. 4, the area of the bonding pad on the semiconductor integrated circuit and the output transistor (for example, P ₄ and P ₅ for driving the capacitor C ₁ (external) of FIG. 4) are used. , N ₂ , N ₃ , and P ₁ , N ₁ for driving the resistors R ₁ , R ₂ (external) are required to be large, and the area occupied by them is much larger than that of the circuit of the present invention. -ing Further, although the present invention requires a stable oscillation circuit such as a crystal oscillation circuit, a large-scale integrated circuit usually requires a stable reference pulse train in addition to the voltage controlled oscillation circuit, and it may be used together with this. Therefore, it does not hinder the implementation of the present invention. In the present invention, the node 116 or 117 of FIG.
By inserting a frequency dividing circuit or a frequency converting circuit in series in the nodes 218 and 219 of FIG. 2 and controlling the frequency dividing ratio and the like by a logic circuit, the free running frequency can be arbitrarily set in the same circuit.

[0020]

As described above, the present invention shows a method for stabilizing an easy voltage controlled oscillator circuit of an integrated circuit, and a voltage controlled oscillator circuit which can be easily incorporated in a digital integrated circuit. By implementing the present invention, the cost and the mounting space can be reduced, and it can greatly contribute to the realization of a device.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

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

FIG. 4 is a diagram showing a conventional voltage controlled oscillator circuit.

[Explanation of symbols]

101.201 first signal synthesizing circuit 103,203 second signal synthesizing circuit 102,202 first voltage control oscillating circuit 104,204 second voltage control oscillating circuit 106,208 phase comparator circuit 105,217 low-pass filter 107 , 211 Reference frequency oscillation circuits 109, 212 First input terminals of the first signal synthesis circuit. Control terminals 110, 214 Second input terminals of first signal combining circuit 111, 213 First input terminals of second signal combining circuit 112, 215 Second input terminals of second signal combining circuit 113, 216 Output terminal

Claims (1)

[Claims] 1. A first voltage-controlled oscillator whose oscillation frequency is controlled by a first synthesized signal; and an oscillation frequency which is controlled by a second synthesized signal and has characteristics equivalent to those of the first voltage-controlled oscillator. A voltage-controlled oscillator circuit comprising: a second voltage-controlled oscillator; and a phase-locked loop having a comparator circuit for comparing the phase of the output of the voltage-controlled oscillator circuit with the phase of the reference signal, the first control signal comprising: A first signal addition circuit that converts the second control signal output from the comparison circuit into a current and adds the current to output the first combined signal; and the second control signal and the reference voltage. And a second signal adding circuit for converting the currents into currents, adding the currents, and outputting the second combined signal.