JPH0566047B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a phase-locked loop (PLL).
Related to voltage controlled oscillator circuits used in applications such as locked loops. The present invention relates to a voltage controlled oscillation circuit, particularly to a circuit designed to stabilize the free run frequency.

A large number of voltage controlled oscillator circuits have been published in the past. Figure 3 shows, as an example, a voltage controlled oscillator circuit used in a one-chip complementary MOS integrated circuit (CMOS IC) for PLL. A control voltage applied to the gate of the N-channel transistor _N1 controls the current flowing into the capacitor _C1 , thereby controlling the oscillation frequency. Resistors R ₁ and R ₂ determine the control voltage sensitivity coefficient and free run frequency, respectively.

As another example, Fig. 4 shows the
1 shows a voltage controlled oscillator circuit known from the publication No. This circuit controls the current flowing into the ring oscillator by the gate voltages of the transistors T ₄₁ to _{T 46} connected to the sources, thereby controlling the oscillation frequency. Although this circuit has the advantage of requiring no external components and requiring less power consumption and mounting space than the circuit shown in FIG. 3, 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.

In general, stability requirements for a voltage controlled oscillator circuit include 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 for CMOS/IC, and where the control voltage is Vc and the reference level voltage is Vs, △Vc is △Vc = Vc - Vs... ...(1) If it is defined, the free run frequency can be rephrased as the oscillation frequency when △Vc=0. The voltage control sensitivity coefficient kv is defined as o=c+kv・△Vc...(2). c is free run frequency, o
is the oscillation frequency of the voltage controlled oscillation circuit.

A drift in the free run frequency c becomes a drift in the cab range of the system in the PLL, and has an adverse effect. In addition, the variation in c due to variations in circuit component constants is too large to be ignored. Conventionally, high-precision components were used at the expense of high costs, or adjustment and matching was done using semi-fixed resistors or semi-fixed capacitors after assembly. The need arose. Furthermore, 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, which has 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 drifts significantly due to these factors. On the other hand, kv can be determined by the relative precision of the circuit components, and even if the absolute precision of element values is not achieved through semiconductor integrated circuit technology, its fluctuation can be reduced by providing relatively sufficient tracking characteristics.

The present invention relates to a circuit system for suppressing the drift of conventional voltage controlled oscillator circuits, and increases the stability of the circuit by reducing fluctuations in the constants (c/kv) of the oscillator circuit due to variations in the constants of circuit components. It's about doing.

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

FIG. 1 is a diagram showing the concept of the present invention. 10
1 and 103 are signal synthesis means designed to have the same characteristics, for example, a signal (hereinafter referred to as a voltage value, a current value, and a signal applied to a terminal 109).
The same story applies to other physical quantities such as electric charge value. )of
V ₁₁ , the signal voltage applied to the terminal 110 is V ₂₁ , and the voltage appearing at the output terminal 114 of the signal synthesis means 101 is V ₀₁ , V ₀₁ = (v ₁₁ , v ₂₁ ) ...(3) is like an arbitrary function. It is a circuit with characteristics. Hereinafter, for 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 signal synthesis means 103
When the voltage at the output terminal 115 of is V ₀₂ , v ₀₂ =av ₁₂ +bv ₂₂ +c (5). 102 and 104 are voltage controlled oscillator circuits with uniform characteristics, and the frequencies F ₁ and F ₂ of the output signals are F ₁ = Kv V ₀₁ + d ……(6) F ₂ = Kv V ₀₂ + d ……(7) (d is a constant) 106 is a phase comparison circuit that compares the phase of the output of the voltage controlled oscillation circuit 104 with the output signal of the oscillation circuit 107 (for example, a crystal oscillation circuit) that oscillates at a stable frequency, and calculates an amount proportional to the phase difference. Outputs the signal. 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 synthesis circuit 103
Negative feedback is provided to the second input terminal 112 of. That is, the second voltage controlled oscillation circuit 104 and the phase comparison circuit 1
06, LPF105, signal synthesis means 103 is PLL
The oscillation frequency of the second voltage controlled oscillation circuit is equal to the oscillation frequency ref of the oscillation circuit 107.
The output frequency of the voltage controlled oscillation circuit 104 can be made to completely match ref and the phase depending on the characteristics of the phase comparator circuit 106 and LPF 105.
It is also possible to not follow sudden changes in . 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. Further, the output frequency and ref of the voltage controlled oscillation circuit 104 follow only the frequency, and there may be an error in the phase, so there is considerable freedom in the circuit configuration. If the oscillation circuit 107 is unstable and has jitter etc., the influence 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 maintain the oscillation frequency of the voltage controlled oscillation circuit 104 at ref.
Further, even if an arbitrary voltage value is applied to the first control terminal 111 of the second signal synthesis means 103, the oscillation frequency of the second voltage controlled oscillation circuit will be ref 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 become equal to the oscillation frequency ref of the voltage controlled oscillation circuit 104. .
As shown in FIG. 1, when the voltage at the second input terminal 112 of the second signal synthesizing means 103 is also applied to the second input terminal 110 of the first signal synthesizing means 101, the first and second signals are synthesized. Since the means and the voltage controlled oscillation circuit have the same characteristics, the oscillation frequency of the first voltage controlled oscillation circuit 102 is equal to ref when the voltage applied to the first input terminal 109 of the first signal synthesizing means 101 is Vs. Become. If ref is set equal to the desired free run frequency c, the oscillation frequency of the voltage controlled oscillation circuit 102 will be c when the voltage at the terminal 109 is Vs. 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 c can be realized.

two signal synthesis means 101, 103 in the circuit;
The discussion has been made on the assumption that the voltage controlled oscillation circuits 102 and 104 have the same characteristics, and this assumption is extremely valid. In particular, when integrated into a monolithic circuit, each circuit can be fabricated with high precision and good symmetry on a chip of 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 you pay sufficient attention to the symmetry of each circuit when designing an integrated circuit,
Fluctuations in each characteristic cancel each other out, making it possible to realize a stable voltage-controlled oscillation 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 which changes the drain current of each transistor by changing the gate voltage of the transistors _T1 and _T2 . T ₁ , T ₂
The drain currents of the transistors are combined (added)
It flows into T ₁₃ and is converted into voltage. This voltage is the control voltage of the first voltage controlled oscillation circuit, and is the control voltage of the first voltage controlled oscillation circuit.
Voltage controlled oscillation circuit 20 composed of transistors
2 is input. (4) The coefficients a and b are multiplied by the input signal as shown in the formula for the beloved device, and it becomes possible to independently set the sensitivity for the two input signals in order to determine the control voltage. In this circuit, a ring oscillator is configured by an odd number of stages of inverters made up of transistors T ₇ , T ₁₀ , T ₈ , T ₁₁ . . . T ₉ , T ₁₂ , and transistors T ₄ , T ₅ , …T ₆ , T ₁₅ , T ₁₆ ,…
By connecting _T17 in series and 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 terminals 212, 2
As the potential of T 14 becomes lower, the drain voltage of T ₁₃ (control voltage of voltage controlled oscillation circuit 202) increases, and the oscillation frequency increases. In other words, a and b are negative in equation (4), and kv is positive in equation (6). terminal 2
If you want to oscillate at a high frequency when the level of 12 and 214 is high, for example, if you reverse the polarity of all the transistors in the circuits of 201 and 202 (P channel transistor to N channel, N channel transistor to P channel), a, b are negative, kv
becomes negative and can be achieved. 205 and 206 are buffer circuits for obtaining outputs.

Reference numerals 203 and 204 are a signal synthesis circuit and a voltage controlled oscillation circuit having the same circuit configuration as 201 and 202, respectively. 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 input to the phase comparison circuit 208 through the buffer 207. Reference numeral 211 is a crystal oscillation circuit that oscillates a frequency ref (=c) that is a reference for the free run frequency. Normally, this signal is the phase comparator circuit 2
The clock signal is inputted to 08 and compared in phase 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 other circuits is different from the desired c, the oscillation frequency of the crystal oscillator circuit 211 can be adjusted by inserting a frequency divider circuit or a frequency converter circuit into one or both of nodes 219 and 218. It is possible to set c to an integer multiple, an integer fraction, the difference between them, an integer equivalent to an integer, etc. The frequency dividing circuit and the frequency converting circuit can be constructed with digital circuits, and no problems will occur when they are integrated 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. First input terminal 21
3 is a resistor that divides the power supply voltage to give the input signal level (reference level) that you want c to oscillate.
R ₁₁ and R ₁₂ are connected. 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 highly accurate voltage source, such as a Zener diode reference voltage, may be connected to this terminal. 1st and 2nd
The second input terminals 214, 215 of the signal synthesis circuit of
The signals are extracted from different points inside the low-pass filter 217 and connected, but the resistor _R4 is
This resistance is necessary for stabilizing the PLL system and is not essentially different from the case shown in FIG.

Looking at the configuration in Figure 2, everything except resistors R ₁₁ to R ₁₅ , capacitors C ₁₁ to _{C 13} , and crystal oscillator X
Consists of MOS transistors. Absolute precision is not required for resistors and capacitors. Therefore, the resistor can be built into the semiconductor integrated circuit. Although it depends on the required oscillation frequency range, it is often possible to incorporate a capacitor _C11 . When a low frequency is required, by connecting a frequency dividing circuit to the output terminal 216, the PLL system can be caused to oscillate at a high frequency, and the capacitance of _C1 can be reduced, making it easy to integrate the 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 may seem that the present invention is considerably more complicated and does not have much merit compared to the conventional example. I don't know. However, the opposite is true; 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. 3, the area of the bonding pad on the semiconductor integrated circuit and the output transistor (for example, P ₄ that drives the capacitor C ₁ (external) shown in Fig. 3), _P5 , _N2 , _N3 ,
P ₁ , N ₁ ) that drive the resistors R ₁ , R ₂ (external) need to be large, and the area occupied by them is much larger than in the circuit of the present invention. In addition, the present invention requires a stable oscillation circuit such as a crystal oscillation circuit, but in large-scale integrated circuits, a stable reference pulse train is often required in addition to the voltage-controlled oscillation circuit, so it is sufficient to use it in combination with the voltage-controlled oscillation circuit. Therefore, this does not pose an obstacle to implementing the present invention. Further, in the present invention, the node 116 or 11 in FIG.
7. By inserting a frequency dividing circuit or a frequency converting circuit in series with nodes 218 and 219 in Fig. 2, and controlling the frequency division ratio etc. with a logic circuit, it is possible to arbitrarily set the free run frequency with the same circuit. can.

In this way, the present invention has shown a method for stabilizing a voltage controlled oscillation circuit that can be easily integrated into an integrated circuit, and has shown a voltage controlled oscillation circuit that can be easily integrated 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.

That is, according to the present invention, the first oscillation circuit can be stably oscillated against fluctuation factors. Furthermore, since the control voltage of the oscillation circuit is converted into a current and then synthesized and converted back into a voltage, it is possible to provide a PLL that supports a wide range of frequencies without changing the characteristics of the PLL.

[Brief explanation of the drawing]

1 and 2 are diagrams showing embodiments of the present invention;
FIG. 4 is a diagram showing a conventional voltage controlled oscillation circuit. 101, 201...first signal synthesis circuit, 10
3,203...second signal synthesis circuit, 102,2
02...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 first signal synthesis circuit, control terminal, 110,214... second input terminal of the first signal synthesis circuit, 111,2
13...first input terminal of the second signal synthesis circuit,
112, 215... Second input terminal of the second signal synthesis circuit, 113, 216... Output terminal.

Claims (1)

[Claims] 1. A first phase-locked loop that has a first voltage-controlled oscillator whose oscillation frequency is controlled by a first composite signal and is synchronized with an input signal, and a first phase-locked loop that is equivalent to the first voltage-controlled oscillator. In the oscillation circuit, the oscillation circuit includes a second voltage-controlled oscillator whose oscillation frequency is controlled by the second composite signal and a second phase-locked loop synchronized with the reference signal. a second control signal generated within the second phase-locked loop for synchronizing the reference signal with the output of the second voltage-controlled oscillator generated within the second phase-locked loop; a first signal addition circuit that converts each of the signals into currents and adds them to output the first composite signal; and a first signal addition circuit that converts each of the second control signal and the reference voltage to currents and adds them to output the first composite signal, and outputs the second composite signal. An oscillation circuit characterized in that it has a second signal addition circuit that outputs.