JP3216610B2 - Programmable crystal oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator for obtaining a stable oscillation frequency, and more particularly to a programmable crystal oscillator whose oscillation frequency oscillates at a predetermined frequency in response to a control signal input.

[0002]

2. Description of the Related Art A conventional programmable oscillator employs a method of varying the frequency of the output of a crystal oscillator using a programmable frequency divider or a method of varying the frequency using a synthesizer using a PLL circuit.

For example, FIG. 7 is a diagram showing a black diagram of a programmable crystal oscillator using a programmable frequency divider for the output of the crystal oscillator. In this figure, a programmable frequency divider 113 whose frequency division number changes under the control of the CPU 112 is connected to the oscillation output of the crystal oscillation circuit 111, and the output of the frequency divider 113 is amplified and output by the amplifier circuit 114. ing.

FIG. 8 is a block diagram showing a synthesizer type programmable oscillator using a PLL circuit. In the figure, the output of the crystal oscillation circuit 111 is input to the reference signal of the phase locked loop 115. Also, the result of the phase comparison input to the phase comparison circuit in the phase synchronization circuit 115 is output via the LPF 116 to the voltage controlled oscillator 1.
The oscillation frequency is controlled by inputting the signal to an input terminal 17. The output of the voltage controlled oscillator 117 is also input to the prescaler 118.
In the variable frequency operation, a control signal from the CPU 112 is input to the phase locked loop 115 and the programmable frequency divider inside the phase locked loop 115 and the frequency divider of the prescaler 118 are controlled to control the oscillation frequency.

[0005]

In the prior art described above, in the configuration shown in FIG. 7 using a programmable frequency divider, the frequency at which the crystal oscillator in the crystal oscillator 111 operates stably usually ranges from several MHz. Since the frequency is about 10 MHz, the maximum frequency is limited to the maximum frequency of the crystal oscillator. For this reason, there was a problem that the operating frequency could not be operated up to a high frequency.

Further, the configuration shown in FIG. 8 using a PLL can function as a high-frequency oscillator because a voltage-controlled oscillator is used. However, since two types of oscillators, a reference oscillator and a voltage-controlled oscillator, are required, there is a problem that the size and the price cannot be reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a programmable crystal oscillator which is small and lightweight, and which can programmably vary the oscillation frequency in a high frequency band.

[0008]

In order to solve the above-mentioned problems, a programmable crystal oscillator according to the present invention has a first control means for controlling an oscillation frequency of a variable crystal oscillation circuit according to a frequency control signal inputted from the outside. And a second control means for selecting and outputting a fundamental wave or a high-order high frequency of the oscillation frequency, and matching the center frequency of the frequency variable filter with the frequency of the high-order harmonic selected by the second control means. A third control means for controlling the output level of the third control means, and a fourth control means for compensating a decrease in the output level of the third control means from the fundamental wave.
Is provided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the main features of the programmable crystal oscillator of the present invention will be described below.

The oscillation frequency of the variable crystal oscillation circuit is programmably varied according to a frequency control signal input from the outside and output. In particular, when the frequency control signal selects a high-order harmonic, a high-order harmonic route is selected by the switching circuit, and the oscillation frequency of the high-order harmonic is adjusted by a frequency variable control filter whose center frequency matches the oscillation frequency. Is selected. In addition, the variable amplifier circuit compensates for a decrease in the oscillation output level with respect to the fundamental wave, and widens the variable frequency range. These controls are automatically controlled by a control circuit based on a frequency control signal.

FIG. 3 is a block diagram showing the configuration of such a programmable crystal oscillator according to the present invention. In the figure, reference numeral 1 denotes a variable crystal oscillation circuit, which receives an oscillation frequency control signal 61 and changes the oscillation frequency. Reference numeral 2 denotes a frequency variable control filter having a band-pass filter (BPF) characteristic. The center frequency of the filter is changed by receiving the filter control signal 63 to select a higher-order harmonic frequency. A variable amplifier 3 receives the gain control signal 64 and compensates for a decrease in level from the fundamental wave when a higher-order harmonic is selected.
Reference numeral 4 denotes a waveform shaping circuit, which shapes an analog signal to convert the waveform into a binary digital signal and outputs it. Also, 5-1
5-2 is a switching circuit for switching the output of the variable crystal oscillator 1 to one of a fundamental wave and a higher harmonic. A control circuit 6 receives a frequency control signal 65 (parallel data) from the outside and performs a control operation relating to a predetermined oscillation frequency. This frequency control signal 65 is a fundamental oscillation frequency (including a variable frequency) that can be oscillated by a programmable crystal oscillator.
And a signal obtained by converting the higher-order frequency into data at a predetermined frequency step. If the frequency control signal 65 is data within the variable frequency range of the fundamental wave, the switching circuits 5-1 and 5-
2 is switched to select the fundamental signal route. If the frequency control signal 65 is in the range of higher harmonics, the switching circuits 5-1 and 5-2 are switched so as to select a higher harmonic route, and the center frequency of the frequency variable control filter 2 is set to the oscillation frequency. Control so that it becomes frequency. Further, the variable amplifier 3 is used to compensate for a decrease in gain in that case.
To control the gain.

The operation of the above-described programmable crystal oscillator will be described below with reference to the drawings.

[0013]

In order to solve the above-mentioned problems, the present invention provides a method according to an externally input frequency control signal.
A variable crystal oscillation circuit whose oscillation frequency is controlled by
Branching the output of the variable crystal oscillation circuit,
The frequency for selecting the higher harmonic of the oscillation frequency for the output of
Output by connecting a variable filter or output as it is
Switching means for switching between the two.

FIG. 3 is a diagram showing the relationship between the oscillation frequency control signal 51 and the oscillation frequency in the fundamental wave of the variable crystal oscillation circuit 1. As shown in this figure, the oscillation frequencies f0... F at the control voltages V0.
Although n is obtained, this characteristic varies even when the same voltage is input because the variable capacitance diode 13 and the crystal oscillator have variations. For this reason, the oscillation frequency of the variable crystal oscillation circuit 1 is measured in advance, and the characteristic of the oscillation frequency control signal 51 versus the oscillation frequency is input to the memory in the control device. That is, the switching circuit 5 is controlled by the switching circuit control signal 62 from the control circuit 6 for each programmable crystal oscillator.
Is switched to the fundamental wave route as shown in FIG. Then, a counter is connected to the output 7 to measure the frequency of the fundamental wave, and the measurement result (data signal) from the counter is input to the memory in the control circuit. The memory has a control voltage V
The oscillation frequencies f0... Fn with respect to 0... Vn are input.

FIG. 4 is a diagram showing the relationship between the output level of the fundamental wave and the higher harmonics of the oscillation frequency. In this figure,
With respect to the output level of the fundamental frequency f0.
The output levels of the second harmonics 2f0... 2fn are reduced by L2. .. 3fn are L
The output level has decreased by three. Similarly, other higher-order harmonics have similar characteristics.

The control circuit 6 oscillates the oscillation frequency control signal 51 to the higher harmonics such as the second, third and fourth harmonics based on the data of the oscillation frequency control signal 51 of the fundamental wave and the oscillation frequency characteristic stored in the memory. Frequency 2f0 ... 2fn, 3f0 ...
3fn, ... are calculated. FIG. 4 shows that the output level of the higher-order harmonic does not need to be exactly equal to the fundamental wave level, as described later.
LN is determined from known harmonic characteristics, and it is assumed that all the programmable crystal oscillators have the same output level reduction.

As described above, when the frequency control signal 66 selects the higher harmonic, the control circuit 6 switches the switching circuit 5
The filter control signal 63 is set so that the center frequency of the frequency variable control filter 2 corresponds to the required high-order harmonic oscillation frequency so that the high-order harmonic route can be selected to select the above-described high-order harmonic oscillation frequency. Output.

FIG. 5 is a block diagram showing an example of the frequency variable control filter 2. As shown in FIG. Variable frequency control filter 2
Is the inductance 25, 26, 31 and the capacitor 2
4, 28, 29 and variable capacitance diodes 20, 27, 3
0 and bias resistors 21, 22, and 23. The filter control signal 63 from the control circuit 6 is input to the control signal input 32 shown in FIG.
By applying a predetermined voltage to 0, 27, and 30 to control the value of current flowing through each of the variable capacitance diodes 20, 27, and 30, the capacitance value is varied and the center frequency of the filter is controlled.

The variable amplifier 3 has gains L1... Ln so as to compensate for the above-mentioned level drop L1... Ln with respect to the higher harmonic fundamental wave by the gain control signal 64 from the control circuit 6. .

Since the harmonic level of the variable crystal oscillation circuit 1 varies due to the characteristics of the transistor 16 and the high-frequency characteristics of the capacitor and the like, the gain is varied for each individual circuit so as to compensate for this variation to match the fundamental level. There is a need to. However, in the present invention, although the output of the switching circuit 5 is input to the waveform shaping circuit 4, it is not necessary to accurately perform gain compensation since the presence or absence of a signal can be detected if the output is higher than a specified threshold voltage. . For this reason,
The gain for higher harmonics is the value L1
Ln is used for all the variable crystal oscillation circuits 1.

The operation of the above-described programmable crystal oscillator when the third harmonic oscillation frequency is input from the frequency control signal 65 will be described with reference to FIG.

FIG. 6A shows the characteristics of the oscillation output of the variable crystal oscillation circuit 1. Since the third harmonic is selected, the control circuit 6 controls the switching circuits 5-1 and 5-2 so that the output of the variable crystal oscillation circuit 1 is on the higher harmonic root side. Then, the control circuit 6 controls the filter control signal 62 so that the center frequency of the frequency variable control filter 2 becomes the center frequency of the third harmonic components 3f0... 3fn as shown in FIG. .

The control circuit 6 controls the gain control signal 64 so that the gain of the variable controller 3 becomes L3 as shown in FIG. 6C.

Finally, the oscillation frequency of the third harmonic components 3f0... 3fn in FIG.
The signal is input to the waveform shaping circuit 4, is converted into a digital signal, and is output to the output 7.

[0025]

The programmable crystal oscillator of the present invention has
Since a high-frequency oscillation output is obtained by using the higher-order harmonics of the crystal oscillator, a high-frequency oscillator with good frequency stability can be provided. Further, since a VCO and a crystal oscillator are not required unlike the prior art, it is possible to reduce the size and weight and to have good phase noise characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing a block diagram of the present invention.

FIG. 2 is a block diagram showing a variable crystal oscillation circuit 1 of FIG. 1;

FIG. 3 is a diagram showing characteristics of an oscillation frequency versus an oscillation frequency control signal of the variable crystal oscillation circuit 1 of FIG.

4 is a diagram showing an oscillation frequency versus an output level of the variable crystal oscillation circuit 1 of FIG.

FIG. 5 is a diagram showing a block diagram of the variable frequency control filter of FIG. 1;

FIG. 6 is a diagram illustrating selection of a third harmonic frequency.

FIG. 7 is a diagram showing a block diagram of a conventional programmable oscillator.

FIG. 8 is a block diagram showing another conventional programmable oscillator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable crystal oscillation circuit 2 Variable frequency control filter 3 Variable amplifier 4 Waveform shaping circuit 5 Switching circuit 6 Control circuit 7 Output

Claims (3)

(57) [Claims] 1. In response to a frequency control signal input from the outside
A variable crystal oscillation circuit whose oscillation frequency is controlled by
Branching the output of the variable crystal oscillation circuit,
The frequency for selecting the higher harmonic of the oscillation frequency for the output of
Output by connecting a variable filter or output as it is
A programmable crystal oscillator comprising switching means for switching between the two . 2. The output of the frequency variable filter is further increased.
Providing a width gauge to adjust the output level of the higher harmonic
Amplify to the level of the fundamental wave of frequency
The programmable crystal oscillator according to claim 1 . Wherein the programmable crystal oscillator, in advance before
The output of the variable crystal oscillation circuit is output
Means to measure and store the oscillation frequency for a number of control signals
2. The programmable crystal oscillator according to claim 1, comprising: