JPS6224968Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a circuit that switches a crystal resonator using a bias voltage of a transistor type crystal oscillator.

Figure 1 is a circuit diagram showing an example of a conventional switching circuit for a crystal resonator, where SW is a changeover switch, X1 and X2 are crystals, D1 and D2 are switching diodes, L1, L2, and L3 are chain coils, and R1 is a current Limiting resistors, R4 and R7 are base bias resistors of transistor TR1, R2 and R3 are reverse bias resistors, R5 is emitter resistor, R6 is load resistor,
C1, C2, C5, C7 are bypass capacitors,
C3 is a coupling capacitor, and C4 and C6 are feedback capacitors for oscillation.

Next, regarding the operation, the case where the switch SW is switched to terminal 1 and the crystal X1 is selected will be described.
First, when switch SW is selected as terminal 1, the DC power supply voltage is
3. It is connected between these and ground via the diode D1 and the chiyoke coil L1. Therefore, a current approximately determined by the current limiting resistor R1 flows through this loop, and the crystal X1 is selected. As a result, the crystal X1 is inserted between the base and collector of the transistor TR1, causing oscillation, which is output via the load resistor R6. In addition, the power supply and resistance R
1. The loop of the chiyoke coil L3, diode D2 and chiyoke coil L2 is not conductive because the terminal 2 of the switch SW is open, and the crystal X2
is not selected.

Among these, the coils L1, L2, and L3 must have reactances sufficiently large for the oscillation frequency, and the inductance value must be selected so as to reduce the influence on the oscillation circuit.

Therefore, as the oscillation frequency becomes lower, the inductance of the chiyoke coils L1, L2, and L3 must be increased, but the influence on the oscillation circuit becomes greater due to a decrease in the self-resonant frequency of the coils themselves and an increase in stray capacitance. In addition, since the shape becomes large, there are problems such as a worsening of the space factor.

The present invention aims to eliminate these drawbacks and utilizes the bias voltage of the oscillation transistor to turn on the switching diode, and will be explained below with reference to the drawings.

Figure 2 is a circuit diagram showing an embodiment of the present invention.
The same symbols as in the figure indicate the same parts. Here, the oscillation circuit using the transistor TR1 is the same as the conventional circuit shown in FIG.

The present invention uses base current bias resistors R10 and R20 instead of the chiyoke coils L1 and L2, and the bias resistors R10 and R20 and R
The resistance value of 4 is set so that the bias of the oscillation circuit of the transistor TR1 is optimized. Also, the resistance R
2, R3 are for reverse bias of switching diodes D1, D2, and the resistance values are usually R10, R20, R
It shall be sufficiently larger than 4. When crystal oscillator X1 is selected based on switching information, R4→D1→R10
Current flows through the switching diode D1 in the order of
turns on. At the same time, the transistor TR of the oscillation circuit
A bias current flows through the base of X1, and the crystal X1 enters the base and collector, causing oscillation.

Also, switching diode D2 is a switch.
When terminal 2 of SW is open, reverse bias resistor R
3, it becomes reverse biased, the switching diode D2 turns off, and the crystal resonator X2 becomes unrelated to oscillation. Although the example in FIG. 2 shows the case of two channels, it is clear that similar results can be obtained even if the number of crystals is increased.

Therefore, in the present invention, the resistors R10 and R20 are included as the bias resistors at the base of the transistor TR1 and the bias resistors for switching the diodes D1 and D2, so that the influence of the inductance caused by the choke coil as shown in FIG. 1 is reduced.

As explained above, according to the present invention, since the switching diode is switched using the bias voltage, the influence on the oscillation circuit is reduced compared to the case where a choke coil or the like is used, and the oscillation circuit becomes stable. Further, by reducing the number of parts, effects such as improved reliability can be obtained.

[Brief explanation of the drawing]

FIG. 1 shows an example of a conventional switching circuit for a crystal resonator using a diode, and FIG. 2 shows a switching circuit for a crystal resonator using a diode according to the present invention. SW...Switch, X1, X2...Crystal resonator, D1, D2...Diode, TR1...Oscillation transistor, R4, R10, R20...Bias resistor, L1, L2...Chiyoke coil.

Claims (1)

[Scope of utility model registration request] In a crystal resonator switching circuit in which at least two or more crystal resonators are provided between the base and collector of an oscillation transistor and these are switched by a changeover switch, a diode is connected for each resonator between the base and the crystal resonator. A crystal resonator switching circuit characterized in that a resistor for base biasing the oscillation transistor is provided at a connection point between each of the diodes and the resonator, and the resistor is connected to each terminal of the switching switch.