JPH04211519A - Voltage control oscillation circuit - Google Patents

Abstract

PURPOSE:To suppress the drifting of free-run frequency and voltage control temperature coefficient and to suppress frequency drifting due to the fluctuation of a circuit constant. CONSTITUTION:The circuit consists of a means 101 synthesizing a signal inputted to first and second terminals 109 and 110, a second means 103 having the same characteristics as that of the first means 101, a first oscillation circuit 102 in which oscillation frequency is controlled by the output of the signal synthesizing means 101, a second oscillation circuit 104 having the same characteristics as that of the first oscillation circuit, 102, an oscillator 107 of reference frequency, a phase comparation means 106 inputting the reference frequency and the output of the second oscillation means 104, and a filter 105, and voltage set at the reference level is applied to a terminal 111 and control voltage is applied to the terminal 109. A terminal 113 is the output terminal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a phase-locked loop (PLL).
, Phase Locked Loop), etc. The present invention relates to a voltage controlled oscillation circuit, particularly to a circuit designed to stabilize the free run frequency.

0002

2. Description of the Related Art A large number of voltage controlled oscillation circuits have been published in the past. FIG. 3 shows, as an example, a voltage controlled oscillation circuit used in a one-chip complementary MOS integrated circuit (CMOS-IC) for PLL. N-channel transistor N1
The current flowing into the capacitor C1 is controlled by the control voltage applied to the gate of the capacitor C1, thereby controlling the oscillation frequency. Resistors R1 and R2 determine the control voltage sensitivity coefficient and free run frequency, respectively.

[0003] As another example, FIG.
6509 indicates a known voltage controlled oscillation circuit. This circuit controls the current flowing into the ring oscillator by the gate voltages of the transistors T41 to T46 connected to the sources, thereby controlling the oscillation frequency. This circuit has the advantage of requiring no external components and requiring less power consumption and mounting space than the circuit shown in FIG. 4, but it is difficult to create an accurate and stable oscillation circuit. Further, even the circuit shown in FIG. 3 cannot be said to have sufficient stability.

0004

Generally speaking, stability is required for a voltage controlled oscillator circuit in terms of the free run frequency and the voltage control sensitivity coefficient. The former is the oscillation frequency when the voltage (control voltage) applied to the control terminal of the voltage controlled oscillation 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 CMOS/IC.If the control voltage is VC and the reference level voltage is VS, ΔVC is ΔVC=VC-VS... ...If defined as (1), the free-run frequency can be rephrased as the oscillation frequency when ΔVC=0. Voltage control sensitivity coefficient KV is fO=fC+
KV・ΔV (2) Defined as: fC is a free run frequency, and fO is an oscillation frequency of the voltage controlled oscillation circuit.

[0005] The drift of the free run frequency fC is the PLL
In this case, the capture range of the system will drift, causing an adverse effect. In addition, the variation in fC due to variations in circuit component constants is too large to be ignored. Conventionally, high-precision components are used at the expense of high costs, or adjustments and matching are made using semi-fixed resistors or semi-fixed capacitors after assembly. There was a need. Further, when a PLL is configured, a drift in the voltage control sensitivity coefficient KV results in a drift in the response speed of the system, resulting in an adverse effect.

The causes of these drifts include changes in ambient temperature, fluctuations in the power supply used, and changes in component constants over time. In particular, the fluctuation of fC greatly drifts due to these factors. On the other hand, KV can be determined by the relative accuracy of the circuit components, and its fluctuation can be reduced by providing relatively sufficient tracking characteristics using semiconductor integrated circuit technology, etc., even if the element values do not have absolute accuracy.

The present invention relates to a circuit system for suppressing the drift of a conventional voltage controlled oscillator circuit, and the oscillation circuit constant (fC,
The purpose of this invention is to reduce fluctuations in KV) and increase the stability of the circuit.

Another object of the present invention is to provide a voltage controlled oscillator circuit that can be easily integrated into an integrated circuit by suppressing fluctuations in absolute accuracy of circuit constants.

[0009]

[Means for Solving the Problems] The present invention has at least the following constituent features a. First means-101 for receiving signals applied to the first and second terminals (109, 110), synthesizing and outputting the signals; b. Second means-1 having the same characteristics as the means 101
03 c. a first oscillation circuit whose oscillation frequency is controlled by the signal of the first signal synthesis means 101-102d. The second signal synthesis means 1 has the same characteristics as the oscillation circuit 102.
Second oscillation circuit controlled by signal 03-104 e. The output of the second oscillation circuit 104 is compared in phase with the signal emitted from the reference frequency signal 107, and based on the result, the output of the second oscillation circuit 104 is Second oscillation circuit 10
the second signal synthesizing means 1 to adjust the output frequency of 4;
A signal is applied to the second input terminal 112 of 03. Further, a level signal serving as a reference level is supplied to the first input terminal 111 of the second signal synthesizing means 103, and the second input terminal 110 of the first signal synthesizing means 101 is connected to the second signal synthesizing means. 103 provides a signal to be applied to a second input terminal 112 of 103 . Further, the first input terminal 109 of the first signal synthesizing means 101 is used as a control terminal, and the first oscillation circuit 102
It is characterized in that the output is the output.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the concept of the present invention. 101
, 103 are signal synthesis means designed to have the same characteristics, and for example, a signal (hereinafter referred to as a voltage value) applied to a terminal 109. The same applies to other physical quantities such as a current value and a charge value. ) is V11, the signal voltage applied to the terminal 110 is V21, and the output terminal 114 of the signal synthesis means 101 is
Letting the voltage appearing at V01 be V01, V01=f(V11, V21) (3) f is a circuit having characteristics like an arbitrary function. Below is V for simplicity.
01=aV11+bV21+c...(4). (a, b, c are constants) Similarly, when the voltages applied to the terminals 111 and 112 are V12 and V22, respectively, and the voltage at the output terminal 115 of the signal synthesizing means 103 is V02, V02=aV12+bV22+c (5) shall be. 102 and 104 are voltage controlled oscillator circuits with uniform characteristics, and the output signal frequencies F1 and F2 are F1=KV V0
1+d …………………(6) F2=KV V02+d
.........(7) (d is a constant). A phase comparison circuit 107 compares the phases of 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 to the phase difference. A low pass filter (LPF) 105 is normally inserted to extract only desired signal components from the output of the phase comparison circuit. The output of the LPF 105 is sent to the second signal synthesizer circuit 103.
Negative feedback is provided to the input terminal 112 of. That is, the second voltage controlled oscillation circuit 104, the phase comparison circuit 106, and the LPF 105
, the signal synthesis means 103 constitutes a PLL, and the oscillation frequency of the second voltage controlled oscillation circuit is the oscillation frequency f of the oscillation circuit 107.
It becomes equal to ref. The output frequency of the voltage controlled oscillation circuit 104 can be completely matched with fref even in phase due to the characteristics of the phase comparator circuit 106 and the LPF 105.
Further, it is also possible to avoid following sudden changes in fref. Since the oscillation circuit 107 is normally a circuit that generates sufficiently stable oscillation, there is no problem even if the response of the system is made faster. Also, the output frequency of the voltage controlled oscillation circuit 104 and f
Since ref follows only the frequency and there may be an error in the phase, the circuit configuration has a considerable degree of freedom. Oscillation circuit 107
If the signal is unstable and has jitter, etc., the effect can be reduced by system design.

Now, let us consider a case where the free run frequency of the voltage controlled oscillation circuit 104 fluctuates due to fluctuations in power supply voltage, temperature characteristics, changes over time, and the like. At this time, the system automatically increases or decreases the voltage applied to the terminal 112 to
The oscillation frequency of 04 is maintained at fref. Further, even if an arbitrary voltage value is applied to the first control terminal 111 of the second signal synthesizing means 103, the oscillation frequency of the second voltage controlled oscillation circuit will be fref regardless of the voltage value. Voltage will be adjusted automatically.

Therefore, when the reference voltage VS is applied to the first input terminal 111 of the second signal synthesis circuit, the level of the second input terminal 112 is automatically adjusted to match the oscillation frequency fref of the voltage controlled oscillation circuit 104. be equal. As shown in FIG. 1, the second input terminal 112 of the second signal combining means 103
is applied to the second input terminal 1 of the first signal combining means 101.
10, since the first and second signal synthesis means and the voltage controlled oscillation circuit have the same characteristics, the oscillation frequency of the first voltage controlled oscillation circuit 102 is the same as that of the first signal synthesis means 101. The voltage applied to the input terminal 109 is VS
When , it becomes fref. If fref is set equal to the desired free run frequency fC, the oscillation frequency of the voltage controlled oscillation circuit 102 will be fC when the voltage at the terminal 109 is VS.
becomes. Therefore, if the entire circuit of FIG. 1 is made into a voltage controlled oscillator circuit with terminal 109 as a control terminal and terminal 113 as an output terminal, a voltage controlled circuit with a free run frequency of fC can be realized. Two signal synthesis means 101, 10 in the circuit
3. The discussion has been made on the assumption that the voltage controlled oscillation circuits 102 and 104 have the same characteristics, but this assumption is extremely valid. In particular, when fabricated into a monolithic integrated circuit, each can be fabricated with high precision and good symmetry on a chip several millimeters square. Since each circuit is manufactured at the same time, even if there is a change over time, the elapsed time is the same, and the characteristics are unlikely to differ from each other. In addition, the same power source is used in response to changes in power supply voltage and temperature, and since they are located very close to each other, it is unlikely that temperature differences will occur between the two and the characteristics will differ. If sufficient consideration is given to the symmetry of each circuit when designing an integrated circuit, variations in each characteristic will cancel each other out, making it possible to realize a stable voltage-controlled oscillator circuit with little drift.

FIG. 2 is a diagram showing a specific example of a voltage controlled oscillation circuit that can be realized by a semiconductor integrated circuit based on the above idea of the present invention. 201 is a signal synthesis circuit that changes the drain current of each transistor by changing the gate voltage of the transistors T1 and T2. The drain currents of T1 and T2 are combined (added) and flow into the transistor T13, where it is converted into a voltage. This voltage is the control voltage of the first voltage controlled oscillation circuit, and is input to the voltage controlled oscillation circuit 202 composed of MOS transistors. This circuit is a transistor T
7, T10, T8, T11,...T9, T12 constitute a ring oscillator with an odd number of stages of inverters, and the source of each transistor and further transistors T4, T5,...T6, T15, T16,...T17 are connected in series. By controlling the gate potential of these transistors, the current flowing into the ring oscillator from the power supply is controlled, and the oscillation frequency is controlled. In the example of the present invention, the lower the potential of the terminals 212 and 214, the higher the drain voltage of T13 (the control voltage of the voltage controlled oscillation circuit 202) and the higher the oscillation frequency. That is, in equation (4), a
, b are negative, and KV is positive in equation (6). If you want to oscillate at a high frequency when the level of terminals 212 and 214 is high, for example, if you reverse the polarity of all the transistors in the circuits 201 and 202 (P channel transistor to N channel, N channel transistor to P channel), This can be achieved when a and b are negative and KV is negative. 205
, 206 is a buffer circuit for obtaining an output.

[0014] 203 and 204 are 201 and 202, respectively.
This is a signal synthesis circuit and a voltage controlled oscillator circuit with a circuit configuration similar to that of . Since the internal configuration is the same, the internal parts are omitted in the figure. The output of the second voltage controlled oscillation circuit is the buffer 207
The signal is input to the phase comparator circuit 208 through. 211 is a crystal oscillator circuit, and the frequency fre is the reference for the free run frequency.
This is an oscillation circuit that oscillates f (=fC). Normally, this signal is input to the phase comparator circuit 208, where it is phase-compared with the output of the second voltage-controlled oscillation circuit 204, and is also shared with the timing clock, system clock, etc. of other circuits. If the frequency of the clock signal etc. required by another circuit is different from the desired fC, the node 219 or 218
By inserting a frequency divider circuit or a frequency conversion circuit into one or both of them, it is possible to set fC to an integer multiple of the oscillation frequency of the crystal oscillation circuit 211, an integer fraction, the difference thereof, an integer of an integer, etc. It is. The frequency conversion circuit and the frequency conversion circuit can be constructed with digital circuits, and there will be no problem when fabricating them into semiconductor integrated circuits. A low-pass filter 217 removes high frequency components contained in the output of the phase comparison circuit 208. The output is fed back to the second input terminal 215 of the second signal synthesis circuit 203. Resistors R11 and R12 are connected to the first input terminal 213 for dividing the power supply voltage to provide an input signal level (reference level) at which fC is desired to oscillate. Although it is difficult to make a resistor accurately in a semiconductor integrated circuit, it is possible to make a resistor with very high relative accuracy. A more accurate voltage source, such as a Zener diode reference voltage, may be connected to this terminal. Signals are extracted from different points inside the low-pass filter 217 and connected to the second input terminals 214 and 215 of the signal synthesis circuit for the first and second signals, and the resistor R4 is used to stabilize the PLL system. This resistance is not essentially different from that shown in FIG.

Looking at the configuration of FIG. 2, the resistors R11 to R15,
All components except capacitors C11 to C13 and crystal oscillator X are composed of MOS transistors. Absolute precision is not required for resistors and capacitors. Therefore, the resistor can be built into the semiconductor integrated circuit. Further, although it depends on the required oscillation frequency range, it is often possible to incorporate the capacitor C11. When a low frequency is required, by connecting a frequency divider circuit to the output terminal 216, the PLL
If the system is made to oscillate at a high frequency, the capacitance of C1 can be reduced and it can be easily integrated into an integrated circuit.

As described above, according to the present invention, an extremely stable voltage controlled oscillation circuit can be realized without using high precision components. Since there is no need to use high-precision parts, it is extremely easy to integrate semiconductor circuits, which has great advantages in terms of packaging and manufacturing.

Comparing the example according to the present invention (FIGS. 1 and 2) and the conventional example (FIGS. 3 and 4), it appears that the present invention is considerably more complicated and does not have much advantage over the conventional example. May. However, the fact is the opposite; when the circuit of FIG. 2 is constructed on a semiconductor integrated circuit, the area occupied on the chip is small. When external components are required, as in the conventional example shown in FIG. , P1, N1) that drive the resistors R1, R2 (external) are required, and the area occupied by them is much larger than that of the circuit of the present invention. Furthermore, although the present invention requires a stable oscillation circuit such as a crystal oscillation circuit, in large-scale integrated circuits, a stable reference pulse train is often required in addition to the voltage-controlled oscillation circuit, and it is sufficient to use this in combination with the voltage-controlled oscillation circuit. Therefore, it does not pose an obstacle to implementing the present invention. Further, in the present invention, the node 116 or 117 in FIG.
By inserting a frequency dividing circuit or a frequency converting circuit in series with the nodes 218 and 219 in FIG. 2 and controlling the frequency division ratio and the like with a logic circuit, it is possible to arbitrarily set the free run frequency using the same circuit.

[0018]

As described above, the present invention has shown a method for easily stabilizing a voltage controlled oscillation circuit in an integrated circuit, and has shown a voltage controlled oscillation circuit that can be easily incorporated into a digital integrated circuit. By implementing the present invention, costs and mounting space can be reduced and it can greatly contribute to the realization of devices.

[Brief explanation of the drawing]

[Figure 1]

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

[Figure 3]

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

[Explanation of symbols]

101, 201...First signal synthesis circuit 103, 203...Second signal synthesis circuit 102, 202...First voltage controlled oscillation circuit 104, 20
4...Second voltage controlled oscillation circuit 106, 208...Phase comparison circuit 105, 217...Low pass filter 107, 211...Reference frequency oscillation circuit 109, 212...First input terminal of the first signal synthesis circuit. Control terminals 110, 214...Second input terminals of the first signal synthesis circuit 111, 213...First input terminals of the second signal synthesis circuit 112, 215...Second input terminal of the second signal synthesis circuit 113,216...output terminal

Claims (1)

[Claims] Claim 1: At least the following constituent requirements a. 1st,
First means-101 for receiving signals applied to second terminals (109, 110), synthesizing and outputting the signals; b. Second means-1 having the same characteristics as the means 101
03 c. a first oscillation circuit whose oscillation frequency is controlled by the signal of the first signal synthesis means 101-102d. The second signal synthesis means 1 has the same characteristics as the oscillation circuit 102.
Second oscillation circuit controlled by signal 03-104 e. The output of the second oscillation circuit 104 is compared in phase with the signal emitted from the reference frequency signal 107, and based on the result, the output of the second oscillation circuit 104 is Second oscillation circuit 10
the second signal synthesizing means 1 to adjust the output frequency of 4;
A signal is applied to the second input terminal 112 of 03. Further, a level signal serving as a reference level is supplied to the first input terminal 111 of the second signal synthesizing means 103, and the second input terminal 110 of the first signal synthesizing means 101 is connected to the second signal synthesizing means. 103 provides a signal to be applied to a second input terminal 112 of 103 . Further, the first input terminal 109 of the first signal synthesizing means 101 is used as a control terminal, and the first oscillation circuit 102
A voltage controlled oscillator circuit characterized in that the output is an output.