JPS5938730Y2 - voltage controlled crystal oscillator - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a voltage controlled crystal oscillator, and particularly to a voltage controlled crystal oscillator that suppresses unnecessary oscillation frequencies.

A circuit example of a conventional third-order overtone voltage-controlled crystal oscillator is shown in FIG.

In Figure 1, 1 is a variable inductance for frequency adjustment, 2 is a varactor diode, 3 is a high frequency blocking resistor, 4 and 5 are voltage control input terminals, 6 and 7 are connection terminals to the oscillator body, 30 is a crystal oscillator, 31.32 is a bias resistor, 37 is a negative feedback resistor, 38 is a resistor that determines the operating current of transistor Q, 42 is a load resistor,
34 and 40 are bypass capacitors, and 35 is a capacitive reactance at the oscillation frequency together with an inductance 39 and a capacitor 41, selects the third overtone frequency, and forms a positive feedback circuit with elements 1.about.2.30 and 33.

36 is a transistor.

Such oscillators often generate unstable frequency spectra other than those controlled by the crystal oscillator, depending on the arrangement of components and the selection of constants.

In order to prevent these self-sustained oscillations, it is common practice to lower the reactance Q consisting of the inductance 1 and the varactor diode 2.

In this case, if the resistor 8 is connected in parallel to the series circuits 1 and 2, as in the circuit 21 in FIG. Since the voltage is divided by resistors 3 and 8, a higher input voltage than usual is required.

In addition, there is the disadvantage that unnecessary energy losses occur as a result of the current flowing through the resistor 8 due to the DC input voltage or the low frequency input voltage.

The object of the present invention is to provide a voltage controlled crystal oscillator that eliminates these drawbacks.

A part of the circuit of the present invention is shown in FIG. 3 below.

This circuit 22 is connected to terminals 6 and 7 in FIG.

As shown in FIG. 3, the series circuit of capacitor 9 and resistor 10 is used to suppress unnecessary and unstable frequency spectrum.

Here, unnecessary frequencies can be suppressed by selecting the value of the capacitor 9 so as to have a reactance sufficiently smaller than that of the resistor 10 at the oscillation frequency.

[Brief explanation of the drawing]

FIG. 1 is a circuit example of a conventional third-order overtone voltage-controlled crystal oscillator. FIG. 2 shows another example of a circuit that corresponds to the part within the broken line in FIG. FIG. 3 shows a circuit of the present invention corresponding to the portion enclosed by the broken line in FIG. In the figure, 1 is a variable inductor, 2 is a varactor diode, 3, 8, 10, 31.32, 37° 38.42 is a resistor, 7, 33, 34, 35, 40° 41 is a capacitor, and 36 is a transistor. be.

Claims (1)

[Scope of utility model registration request] A first circuit in which an inductance and a varactor diode are connected in series is connected in series with a crystal resonator, and the oscillation frequency is controlled by changing the oscillation frequency by a voltage applied to the varactor diode through a resistor at a connection point between the inductance and the varactor diode. A voltage controlled crystal oscillator, characterized in that a second circuit including a capacitor and a resistor connected in series is connected in parallel to the first circuit to suppress unnecessary frequencies other than the oscillation frequency.