JPH0568110U - Variable frequency oscillator - Google Patents

Abstract

(57) [Summary] [Purpose] To realize a variable frequency oscillator circuit with a wide oscillation margin while widening the variable frequency range. In a variable frequency oscillation circuit including an inverter 1 and a crystal oscillator 2, an inductor L connected in series with the crystal oscillator 2, a resistor Rd2 connected in parallel with the inductor L, and an inductor connected in parallel. L and resistance Rd2
And a switch 4 for short-circuiting.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a variable frequency oscillator circuit, and more particularly to a variable frequency oscillator circuit capable of changing an oscillation frequency.

[0002]

[Prior Art]

 Fig. 3 shows a variable frequency oscillator circuit that uses an inverter that has been commonly used. In this figure, 1 is an inverter such as CMOS, 2 is a crystal oscillator, 3 is a buffer, R is a feedback resistor, Rd is a damping resistor, and CL1 and CL2 are load capacitors.

Here, the damping resistor Rd is inserted for the purpose of reducing the power consumption of the circuit, ensuring the amount of phase shift, and lowering the loop gain. In this variable frequency oscillator circuit, an inverter is used as an amplifier circuit to form an oscillator circuit.

[0004]

[Problems to be solved by the device]

 The damping resistor Rd having the above-mentioned configuration lowers the loop gain in order to suppress abnormal oscillation, but there is a problem in that the oscillation margin becomes small when the resistance value is increased.

In addition, in the oscillation circuit using the crystal oscillator, if the oscillation frequency is variable, it is difficult to expand the variable range. The present invention has been made in view of the above problems of the prior art, and an object thereof is to realize a frequency variable oscillation circuit having a large oscillation margin while widening the frequency variable range.

[0006]

[Means for Solving the Problems] Means for solving the above-mentioned problems are as follows: In a frequency variable oscillation circuit including an inverter and a crystal unit, an inductor connected in series with the crystal unit and connected in parallel with the inductor. And a switch that short-circuits the inductor and the resistor connected in parallel.

[0007]

[Action]

 In a variable frequency oscillator that uses an inverter, the inductor is connected in series to the crystal unit, which widens the variable frequency range and increases the oscillation margin.

[0008]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a block diagram showing an embodiment of the present invention as a PLL configuration, FIG. 2 is a waveform diagram showing signal waveforms of respective parts, and FIG. 3 is a waveform diagram showing details of waveforms. In these figures, 1 is an inverter, 2 is a crystal oscillator, 3 is a buffer, 4 is a switch arranged in parallel with the inductor L so as to be turned off by an instruction from the outside, and Rd is for suppressing abnormal oscillation. Damping resistor, L is an inductor connected in series with the crystal unit 2, Rd2 is a second damping resistor connected in parallel with the inductor L, R is a feedback resistor, CL1 and CL2 are load capacitors, and 5 is a frequency CLK2. An oscillator that oscillates, 6 is a phase comparator that compares the oscillation output of the oscillator 5 with the output of the inverter 3.

The operation of the apparatus of this embodiment having the above-described configuration is as follows. When the output CLK2 of the buffer 3 has a higher frequency than the output CLK1 of the oscillator 5, the output of the phase comparator 6 switches the switch 4 to the off side. As a result, the inductor L is connected in series with the crystal unit 2 and the L component increases, so that the oscillation frequency CLK2 decreases.

Here, when the oscillation frequency CLK2 becomes lower than CLK1, the switch 4 is switched to the ON side according to the phase comparison result of the phase comparator, and the inductor L stops operating. As a result, the oscillation frequency CLK2 becomes high.

By repeating the above operation, CLK2 can be synchronized with CLK1. Further, in this embodiment, the frequency switching means has a structure in which the inductors L are connected in series with each other by vibrating the crystal so that it is possible to increase the oscillation allowance at the same time as decreasing the frequency.

The inventor of the present invention has produced good results when the circuit shown in FIG. 2 is prototyped and tested. Here, the feedback resistance R is 1 MΩ, the damping resistance Rd is 470 Ω, the crystal oscillator 2 is 20 MHz, the load capacitances CL1 and CL2 are 7 pF, the inductor L is 4.7 μH, and the second damping resistance is 7.5 kΩ. In this case, the frequency displacement width was 320 ppm and the oscillation allowance was 1 kΩ or more.

On the other hand, when the frequency is changed in the same manner as in the conventional case by opening / closing the switch 7 and adding the load capacitance CL3 (22 pF), the frequency displacement width is 285 ppm and the oscillation is generated. The allowance was 617Ω.

As described above, according to the configuration of this embodiment, the frequency displacement width is larger than that of the conventional configuration, and the oscillation margin is large.

[0015]

[Effect of the device]

 As described in detail with the examples above, an inductor is inserted in series with the crystal unit, and the state of the inductor can be switched by the switch connected in parallel with this inductor. It is possible to realize a variable frequency oscillator circuit that has a large displacement range and a large oscillation margin.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is an explanatory view showing a test state in one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a conventional device.

[Explanation of symbols]

 1 Inverter 2 Crystal oscillator 3 Inverter (buffer) 4 Switch 5 Oscillator 6 Phase comparator R Feedback resistor Rd Damping resistor CL1, CL2 Load capacitance L Inductor Rd2 Second damping resistor

Claims (1)

[Scope of utility model registration request] 1. An inverter (1) and a crystal unit (2)
In a variable frequency oscillator circuit including: an inductor (L) connected in series with a crystal unit (2)
And a resistor (Rd2) connected in parallel with the inductor (L), and a switch (4) for short-circuiting the inductor (L) and the resistor (Rd2) connected in parallel. circuit.