JPH01222519A - Control system for oscillation circuit - Google Patents

Abstract

PURPOSE:To improve the C/N and the stability of the oscillated frequency by applying an offset voltage having temperature information between a phase comparator and a low pass filter. CONSTITUTION:The offset voltage having temperature information is applied between a phase comparator 10 and a low pass filter 13 and set so that the frequency fluctuation of a voltage controlled oscillator 8 due to the offset voltage is not out of a lock range of a phase locked loop(PLL). Then at the loss of the reference input signal fed to the PLL, the offset voltage applies temperature compensation control. The phase correction with the reference signal is applied to compensate the correction error after temperature compensation at the PLL lock in this way and the oscillator acts like a voltage variable oscillator even at a loss of the reference input signal fed to the PLL. Thus, the stability and the C/N of the oscillated frequency are improved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an oscillation circuit configured as a PLL circuit, and more specifically, to a device that provides highly stable oscillation even when a reference input signal is lost, which is applied to the PLL circuit. It involves controlling the oscillation circuit to obtain the frequency.

(Prior art) In recent years, the quality and density of information has been increasing in fields such as measurement, broadcasting9 communications, and medical care.In order to cope with the high quality and density of information, the oscillation circuits used in them have been increasing. The stability of the launch frequency is increased by temperature compensation or by using a PLL circuit.

FIG. 2 is a diagram showing a conventionally used temperature-compensated quartz crystal device. In the figure, 1 is a temperature detection circuit using a temperature sensing element such as a thermistor or a posistor, and 2 is a voltage controlled crystal oscillator (hereinafter referred to as VCXO).1 As is well known, an oscillator using a crystal is Oscillation due to changes in ambient temperature.

Although the frequency varies in a quadratic or cubic function, in order to suppress the variation in the oscillation frequency, the temperature detection circuit 1 applies a voltage to the VCXO 2 to correct the variation, thereby increasing the stability of the oscillation frequency. there were.

In order to further improve the stability of the oscillation frequency, the method shown in Figure 3 (
Many oscillation circuits using PLL circuits are also used.

In the same figure, 3 is a temperature-compensated voltage variable oscillator (hereinafter referred to as TCVCXO), and the Tcvcxo output is inputted to a frequency divider 4, which divides the frequency to a desired frequency and outputs the output to a phase comparator 5.
Enter. The phase comparator 5 compares the output of the frequency divider 4 with a reference signal based on an atomic standard such as cesium or a reference signal output from a constant temperature oven crystal oscillator (hereinafter referred to as 0CXO), and calculates a signal proportional to the frequency difference. A signal is generated and its output is input to an operational amplifier 6.

The operational amplifier 6 adds the output of the phase comparator and the offset voltage, and after calculation, outputs it to the next stage LPF 7, which passes only the DC component and calculates the 'l'c.
Add a control voltage to VcXO. or.

As is well known, Tcvexo is configured to oscillate at a set frequency while being controlled by a voltage that is the sum of both a compensating voltage that suppresses frequency fluctuations due to ambient temperature and a control voltage of the PLL circuit.

The oscillation circuit configured in this way is 'l'cVcX.

Since it performs temperature compensation on its own and locks the oscillation frequency using the PLL circuit, it is not only possible to obtain a highly stable oscillation frequency, but also to be used even when the reference signal cannot be obtained due to the usage environment, etc. Since the PLL is in a free-running state at the oscillation frequency of the TCVCXO, a somewhat stable oscillation frequency can be obtained.

However, as described above, the TCVCXO receives two independent input information, the temperature compensation control signal and the PLL circuit control signal, and is finally controlled by the voltage of the signal that is a combination of them.

Since the temperature sensing elements such as thermistors or posistors used in the temperature compensation thread are directly connected to the control voltage generation circuit of the oscillator, their phase noise characteristics (hereinafter referred to as C/N ratio) are significantly degraded by their noise. There were drawbacks such as:

(Object of the Invention) The present invention has been made in view of the above-mentioned drawbacks, and is an oscillation circuit having a PLL configuration that has a high C/N ratio and high stability, and which provides a Another object of the present invention is to provide a control method for an oscillation circuit that makes it possible to obtain a temperature-compensated oscillation frequency.

(Summary of the Invention) In order to achieve this object, the present invention applies an offset voltage having temperature information between nine phase comparators and an LPF in an oscillation circuit having a PLL configuration, and also applies an offset voltage having temperature information between the nine phase comparators and the LPF, and The offset voltage is set so that the frequency fluctuation does not deviate from the lock range of the PLL, and measures are taken so that temperature compensation control can be performed using the offset voltage when the reference input signal applied to the PLL is lost.

(Examples) The present invention will be described in detail below based on the embodiments shown in the drawings.

First, in order to facilitate understanding of the present invention, the TCXO conventionally used will be briefly explained.

For example, if the temperature-frequency characteristic of the VCXO configured in the 'l'cXO changes in a cubic curve as shown in Figure 4, the oscillation frequency (hereinafter referred to as the set frequency) at 25°C will be When FO and TA'C, the oscillation frequency becomes FA. In addition, the control voltage characteristics applied to the vcxo are as shown in Fig. 5.Assuming that the control voltage VO necessary when outputting the set frequency FO9 and the control voltage VA required when outputting the frequency FA, TA'C The oscillation frequency FA should be set lower than the set frequency FO by (FO-Fh), and in order to compensate for this frequency fluctuation
) is the control voltage VA” & TCXO temperature detection part #)
This is applied to the VCXO.

That is, if an offset voltage having a characteristic opposite to the oscillation frequency characteristic is applied to the VCXO as shown in FIG. 6 in order to suppress the frequency fluctuation due to the temperature-frequency characteristic of the VCXO, the oscillation frequency of the VCXO will always be the set frequency Fo. be able to maintain.

Furthermore, when a temperature compensated oscillator is used and a PLL configuration is used, it is sufficient to use a '1' cvcxo that is controlled manually by an offset voltage having temperature information and a PLL control voltage; The output signal of the oscillator may cause instantaneous frequency fluctuations due to noise, or
As mentioned above, there were drawbacks such as a significant decrease in /N.

Therefore, the present invention takes measures as shown in FIG.

That is, the VCXO8 with a high C/N ratio is used as an oscillator.

A frequency divider 9 which inputs the VCXO output and divides the frequency to a desired frequency; and a phase comparator 10 which inputs the frequency divider output signal and a reference input signal and generates a voltage proportional to the phase difference. It is composed of an operational amplifier 12 that adds and amplifies the output of the phase comparator and the output of the temperature detection circuit 11, and an LPF 13 that passes only the DC component of the output of the operational amplifier.

That is, in the present invention, the temperature compensation voltage ff is used as the control voltage of the VCXO via the LPF to eliminate noise components generated from temperature sensing elements such as posister or thermistor, thereby achieving a high C/N ratio. This is to obtain oscillation output.

In the oscillation circuit configured in this way, for example, the control voltage characteristics of the VCXO are shown in Figure 7 (oV to 5V, frequency fluctuation rate △ in the operating temperature range (-10°C to +60°C)).
If f/f is ±20ppm as shown in No. 81￥1, then 1
When the ambient temperature is 110 degrees Celsius, the free-running oscillation frequency is +20 ppm with respect to Fo, so with the characteristics shown in Figure 7, the voltage that can output a frequency of -20 ppm higher than the frequency FO at vO is set as 7. The voltage may be applied from the temperature detection circuit 11 shown in FIG. Figure 9 shows the output characteristics of the temperature detection circuit.

If a voltage with such characteristics is applied to the operational amplifier 12 and added to the output from the phase comparator to control the vcxo via the LPF 9, when the vcxo output matches the set frequency and the reference input signal of the phase comparator 10 Even if the phase comparator output signal becomes O at the time of loss, it functions as a TCXO, and when the PLL is locked, the frequency fluctuation due to the temperature change of the VCXO is corrected, and the phase comparison is performed because the frequency matches or approximates the set frequency. The phase detection function in the device is also similar to that of conventional PL.
The same characteristics as those used for L are sufficient.

Furthermore, since noise generated in the temperature detection circuit can be removed through the LPF, its influence on the VCXO is reduced.

9 Although the explanation was given using a crystal oscillator in this embodiment, it is not limited to this (SAW'i! may also be used, and if an oscillator other than a crystal is used, the oscillator It is clear that it is sufficient to apply an offset voltage for temperature compensation between the phase comparator and the LPF from the temperature detection circuit.

(Effects of the Invention) Since the present invention is configured and functions as described above, when the PLL is locked, the phase with the reference signal is corrected to compensate for the correction error after temperature compensation, so the stability of the oscillation frequency is improved. Not only is it possible to obtain a high value and a high /N ratio, it also functions as a TCXO even when the reference input signal supplied to the PLL is lost, so it is very effective in increasing the stability of the oscillation frequency. It is something to play.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an oscillation circuit used in carrying out the present invention, FIGS. 2 and 3 are block diagrams showing the configuration of a conventionally used oscillation circuit, and FIGS.
The figure shows the temperature-frequency characteristics of the crystal oscillator, Figures 5 and 7 show the control voltage characteristics of VCXO, and Figures 6 and 9 show the control voltage characteristics applied to VCXO. be. 1.11...Temperature detection circuit, 2,
8・・・・・・・・・VCXO3・・・・・・・・・T
CXo. 4.9... Frequency divider, 5.10.
・・・・・・Phase comparator, 6.12...
・・・・・・Operation amplifier. 7.13......LPF0 Patent applicant: Toyo Tsushinki Co., Ltd. No. J: -2- No. 3 No. 1A to J S No.? figure

Claims (1)

[Claims] (1) In order to increase the stability of the oscillation frequency of a voltage controlled oscillator (hereinafter referred to as VCO), a frequency divider that inputs the VCO output and divides the frequency to a desired frequency, and a frequency divider output signal and a reference signal. The input phase comparator (hereinafter referred to as PD) and the PD
In an oscillation circuit having a PLL configuration, which includes a low-pass filter (hereinafter referred to as LPF) that inputs an output signal, and inputs the LPF output to the VCO, temperature information is transmitted between the PD and the LPF. 1. A control method for an oscillation circuit characterized by adding an offset voltage having .