JPH03280605A - Variable frequency oscillator - Google Patents

Abstract

PURPOSE:To obtain a stable oscillation signal with simple constitution by adopting the oscillator such that a frequency control signal and a temperature compensation signal are applied separately to each varactor element on the input and output sides of a C-MOS inverter, respectively. CONSTITUTION:A vibrator 4 is provided in parallel with a C-MOS inverter 1 and varactor elements 7, 11 are provided respectively to the input and output side of the C-MOS inverter 1. Moreover, the oscillator is constituted such that a frequency control signal (from control signal terminal 8) is fed to either of the input and output varactor elements and a temperature compensation signal (from transistor(TR) 15) is fed to the other of the input and output varactor elements. Since the frequency control signal and the temperature compensation signal are applied independently from each of input and output sides of the C-MOS inverter to the varactor elements respectively, the mutual effect of both the signals is avoided. Thus, the temperature compensation is implemented with simple constitution and a stable oscillation signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable frequency oscillator used in a PLL or the like that generates a clock signal synchronized with an input signal when processing a video signal, for example.

[Summary of the invention]

The present invention relates to a variable frequency oscillator, and by supplying a frequency control signal to one of the input and output sides of a C-MOS inverter and supplying a temperature compensation signal to the other side, the oscillation frequency can be increased with a simple configuration. This makes it possible to perform temperature compensation and obtain a stable oscillation signal.

[Prior Art] A PLL as shown in FIG. 4 has conventionally been used as a device for generating a clock signal synchronized with an input signal. In the figure, a comparator (42) compares the phase of an input signal supplied to a terminal (41) and a signal from a frequency dividing circuit (46), which will be described later, and the comparison output is sent to a loop filter (43).
A variable frequency oscillator (44) is supplied through the line 17 to generate a clock signal. This clock signal is taken out to the output terminal (45), and the frequency dividing circuit (45)
6), and a signal divided to the frequency of the input signal is supplied to a comparator (42). As a result, a clock signal is generated by multiplying the input signal by the frequency division ratio of the frequency divider circuit (46).

And in such a device, a variable frequency oscillator (4
4) Conventionally, for example, bipolar transistors and CL
A circuit consisting of a combination of resonant circuits is used, and temperature compensation can usually be performed relatively easily in such a circuit.

[Problem to be solved by the invention]

However, in recent years, for example, when processing video signals, it has become necessary to generate a pixel clock signal in synchronization with the horizontal signal of the input video signal. In this case, this pixel clock signal has a high frequency of, for example, 14.318 MHz, and its oscillation signal is required to have high accuracy and stability.

Therefore, for example, a variable frequency oscillator that combines a C-MOS inverter and a crystal resonator has been used. That is, FIG. 5 shows the configuration of an example of the C-MOS
A resistor (52) is connected in series to the inverter (51), a resistor (53) is connected in parallel to the series circuit of the inverter (51) and the resistor (52), and a crystal resonator (54) is connected in parallel to these. A series circuit of a resistor (55) and a resistor (55) are connected. The input side of the inverter (51) is grounded to these parallel circuits through a parallel circuit of a capacitor (56) and an adjustment trimmer capacitor (57).
Further, the output side of the inverter (51) (the other end of the resistor (52)) is grounded through a series circuit of a capacitor (58) and a varicap diode (59).

Thereby, for example, a frequency control signal from the above-mentioned loop filter (43) is supplied to the terminal (60), and a control signal from this terminal (60) is supplied to the varicap diode (59) through the resistor (61). By this,
The capacitance of this diode (59) is changed to control the oscillation frequency of the circuit. The oscillation output from the circuit is connected to the input/output terminals of the inverter (51), the parallel circuit, and the capacitor (
(58) connection point (output terminal (62)
) )be able to.

However, when a C-MOS inverter (51) is used in this circuit, there is a problem in that the propagation delay time varies greatly with respect to the temperature of the C-MOS IC. In other words, Figure 6 shows the temperature characteristics of the propagation delay time of the standard C-MO3IC. When normalized with 25°C as 1 as shown in the figure, for example, at 85°C, the propagation delay time is 1. .It will double in size. Therefore, if the propagation delay time fluctuates as described above, a stable oscillation signal cannot be obtained.

For example, as shown in the figure, a signal for temperature compensation is supplied from the terminal (63) through the resistor (64) to the varicap diode (59), and One possibility is to change the bias of the frequency control signal, but this method has the problem that the frequency variable range changes depending on the temperature.

In other words, Fig. 7 shows, for example, the conversion characteristics of the horizontal axis: control signal potential and the vertical axis: oscillation frequency, and at 25°C.
When the characteristics shown by the solid line are obtained, the control signal is set to the center potential ■. By changing the oscillation frequency from 1 to 2 in the range shown by arrow a, an oscillation frequency that changes in the range shown by arrow 2 with the frequency f as the center can be obtained. However, there are cases where the characteristics change as shown by the broken line due to temperature changes, and in that case, the center potential is changed by the temperature compensation signal. ′, the frequency f. remains unchanged, but the variable range of the oscillation frequency is changed as shown by arrow b', and in this case, the variable range becomes narrower on the lower side of the oscillation frequency.

Similarly, when the characteristics become as shown by the chain line, the variable range on the high frequency side of the oscillation frequency becomes narrow.

Therefore, if the variable range of the oscillation frequency is changed in this way, the signal pull-in range will be changed when, for example, a PLL is configured, resulting in extremely large inconveniences in use.

This application was made in view of these points, and is intended to make it possible to obtain a stable oscillation signal with a simple configuration.

[Means to solve the problem]

In the present invention, a vibrator (4) is provided in parallel to a C-MOS inverter (1), and variable capacitance elements (7) (1) are provided on the input side and output side of the C-MOS inverter, respectively.
1) is provided, and a frequency control signal (terminal (8)) is provided to the variable capacitance element on either the input side or the output side.
), and a temperature compensation signal (transistor (15)) is supplied to the variable capacitance element on either the input side or the output side. .

[Effect]

According to this, the frequency control signal and the temperature compensation signal are supplied independently from the input side and the output side of the C-MOS inverter, so they do not affect each other, and temperature compensation is performed with a simple configuration. This allows a stable oscillation signal to be obtained.

〔Example〕

In Fig. 1, (1) is a C-MOS inverter, and a resistor (2) is connected in series to this inverter (1), and this inverter (1) and resistor (2) are connected in series. A resistor (3) is connected in parallel to the circuit, and further a series circuit of a crystal resonator (4) and a resistor (5) is connected in parallel to these. Furthermore, for these parallel circuits, the output side of the inverter (1) (the other end of the resistor (2)) is connected to the capacitor (
6) and a varicap diode (7) in series. And this Haricap diode (
7) is supplied with a frequency control signal, for example from the above-mentioned loop filter (43), which is supplied to the terminal (8), through the resistor (9).

Furthermore, in this circuit, the input side of the inverter (1) is connected to one end of a capacitor (10), and the other end of this capacitor (10) is connected to a varicap diode (11).
) and a capacitor (12) in a parallel circuit to a power supply terminal (13) to which power supply voltage VCC is supplied. Further, the other end of the capacitor (10) is connected to the collector of a transistor (15) through a resistor (14), and the emitter of this transistor (15) is grounded through a resistor (16). is connected to the power supply terminal (13) through a resistor (17). Furthermore, the power supply terminal (13) is grounded through a series circuit of a resistor (18) and a Zener diode (19), and a resistor (20) is connected in parallel to this Zener diode (19).
, a variable resistor (21), and a resistor (22) are connected in series, and the slider of the variable resistor (21) is connected to the base of the transistor (15). Note that (23) is an output terminal.

Therefore, in this circuit, the oscillation frequency is changed by the frequency control signal supplied to the terminal (8), and the pace emitter voltage 1 of the transistor (15) is changed according to the temperature, and the temperature formed by this is changed. A compensation signal is supplied to the varicap diode (11) to perform temperature compensation.

That is, in this circuit, for example, when the temperature rises, C
- The propagation delay of the MOS inverter (1) increases, and the oscillation frequency fluctuates in a decreasing direction.

On the other hand, as the temperature rises, the voltage of the transistor (15) decreases, and the voltage applied to the Haricap diode (11) increases, which serves to increase the oscillation frequency and perform temperature compensation. .

The numbers in the figure are specific examples of the values of each element, where the power supply voltage cC is 4.4 and the Zener diode (19
) is 1.9■, and the collector potential of the transistor (15) at room temperature is 3■.The change in free run frequency with respect to temperature was experimentally shown by the solid line in FIG. On the other hand, the broken line in the figure shows the case where conventional temperature compensation is not performed, and as is clear from the figure, the oscillation frequency is stabilized by the above-mentioned circuit.

Furthermore, in the circuit described above, frequency control and temperature compensation are performed independently, so that even if the conversion characteristics shown by the solid line in FIG. 3 change to those shown by the broken or chain lines due to temperature changes, Compensation is performed so that the value approaches the solid line, and therefore the variable range of the oscillation frequency is not changed by temperature compensation.

In this way, according to the above circuit, the frequency control signal and the temperature compensation signal are supplied independently from the input side and the output side of the C-MOS inverter, so they do not affect each other and the configuration is simple. Temperature compensation is performed and a stable oscillation signal can be obtained.

Furthermore, by stabilizing the frequency variable range, the variable range can be substantially widened, thereby improving the yield during circuit manufacturing.

Note that the adjustment performed by the trimmer capacitor (57) in the conventional circuit is performed by the variable resistor (21), but this can also be performed by replacing the capacitor (12) with the trimmer capacitor.

Furthermore, in the above-mentioned circuit, by providing the Zener diode (19), the base potential of the transistor (15) is stabilized, thereby making it possible to satisfactorily compensate for fluctuations in the power supply voltage VCC. be.

〔Effect of the invention〕

According to this invention, since the frequency control signal and the temperature compensation signal are independently supplied from the input side and the output side of the C-MOS inverter, they do not affect each other and temperature compensation is performed with a simple configuration. This has made it possible to obtain stable oscillation signals.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an example of a variable frequency oscillator according to the present invention, Fig. 2 is a diagram for explaining its effects, Fig. 3 is a diagram for explaining its operation, and Fig. 4 is a configuration of a PLL. 5 is a configuration diagram of a conventional circuit, FIG. 6 is a temperature characteristic diagram of a C-MO3 IC, and FIG. 7 is a diagram for explaining the conventional operation. (1) is a C-MOS inverter, (2) (3) (5) (
9) (14) (16) (17) (1B) (20
) (22) is a resistor, (4) is a crystal oscillator, (
6) (10) (12) are capacitors, (7) (11)
) is a varicap diode, (8) is a control signal terminal,
(13) is a power supply terminal, (15) is a transistor, (19)
) is a Zener diode, (21) is a variable resistor, (2
3) is an output terminal.

Claims (1)

[Claims] A vibrator is provided in parallel to the C-MOS inverter, and a variable capacitance element is provided on the input side and the output side of the C-MOS inverter, and either one of the input side and the output side is provided. A frequency control signal is supplied to the variable capacitance element on the side thereof, and a temperature compensation signal is supplied to the variable capacitance element on the other side of either the input side or the output side. frequency oscillator.