JPS632484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal oscillator used, for example, in a color signal processing circuit of a video tape recorder, and more particularly to a crystal oscillator having two functions: a reference oscillator and a voltage-controlled oscillator.

FIG. 1a is a block diagram of a color signal processing circuit of a video tape recorder (hereinafter referred to as VTR) using a conventional crystal oscillator during reproduction. In the figure, a color signal input terminal 1 is connected to one input of a first frequency converter 2, the output of which is connected to an output terminal 3 and one input of a phase comparator 4. The output of a reference frequency oscillator 5 is connected to the other input of this phase comparator 4, and the output of this phase comparator 4 is connected to the input of a voltage controlled oscillator 6, and the output of this oscillator 6 is connected to a second frequency. The output of the oscillator 5 is connected to one input of the converter 7, and the output of the oscillator 5 is connected to the other input of the second frequency converter 7. The output of this second frequency converter 7 is connected to the other input of the first frequency converter 2, and is connected to the phase lock groove (hereinafter referred to as
PLL) is configured. The voltage controlled oscillator 6 also forms a closed loop with the mislock detector 8.

Next, the operation during reproduction will be explained, focusing on the oscillator 5 using a crystal resonator.

When the low frequency converted color signal taken out from the head of the VTR is input to the input terminal 1, the output converted to a predetermined frequency by the first frequency converter 2 is taken out from the output terminal 3. At this time, since the color signal taken out from the head contains jitter, the frequency and phase of the output finally taken out from one input of the phase comparator 4, that is, the output terminal 3, are adjusted to the frequency and phase of the reference oscillator 5 using the PLL. The voltage controlled oscillator 6 is operated so as to be locked to the phase and eliminate fluctuations on the time axis. At this time,
Mislock detector 8 prevents the PLL from malfunctioning. Since the reference oscillator 5 in this frequency conversion operation is required to have high frequency stability, an oscillator with a high Q value using a crystal resonator is used.

FIG. 1b is a block diagram of the color signal processing circuit of a VTR during recording. In the figure, a color signal input terminal 1 is connected to one input of a first frequency converter 2, the output of which is connected to an output terminal 3. The input terminal 1 is also connected to one input of a phase comparator 9, the output of which is connected to a voltage controlled oscillator 10 using a crystal resonator, the output of which is connected to one input of a second frequency converter 7. and its output is connected to the other input of the first frequency converter 2. Voltage controlled oscillator 10
The output of the phase comparator 9 is also connected to the other input of the phase comparator 9 to form a PLL. Further, the horizontal synchronizing signal input terminal 11 is connected to the input of a PLL multiplier circuit 12, and the output thereof is connected to the other input of the second frequency converter 7, thereby forming a color signal low frequency conversion circuit.

The operation of the circuit configured as described above during recording will be explained focusing on the oscillator 10 using a crystal resonator. When a color signal is input to the input terminal 1, it is converted into a low frequency converted color signal by the first frequency converter 2, and is taken out from the output terminal 3 and magnetically recorded on a magnetic tape. A PLL comprising a phase comparator 9 and a voltage controlled oscillator 10 such that the output frequency of the controlled oscillator 10 is locked to one input of the phase comparator 9, that is, the frequency and phase of the color signal.
works. In this case, the voltage controlled oscillator 10 is
In order to ensure the necessary lock range, etc., a voltage controlled oscillator using a crystal resonator is used, although the Q value is lower than that of the reference oscillator 5 during reproduction, but high frequency stability is required.

As mentioned above, the conventional VTR color signal processing circuit has
A drawback is that an oscillator using two crystal oscillators is required, the reference oscillator 5 using a crystal oscillator exclusively for playback, and the voltage controlled oscillator 10 using a crystal oscillator exclusively for recording, which increases the cost of the oscillator. It was hot.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and includes a filter composed of a crystal resonator and an impedance means including a reactance component, and one end of this filter is connected to an input end. an amplifier, and a voltage-controlled phase shifter in which an output end of the amplifier is connected to an input end, the other end of the filter being switchably connected to the output end of the amplifier or the output end of the phase shifter. The purpose of this invention is to obtain a crystal oscillator having two functions as a reference oscillator and a voltage-controlled oscillator using one crystal oscillator.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram of a crystal oscillator used in the color signal processing circuit of a VTR. 22
The output of the switch 23 is connected to the other terminal 23b of the switch 23. The common terminal 23c of the switch 23 is connected to one terminal of a crystal oscillator 24, the other terminal of this is connected to one terminal of a capacitor 25 having a capacitance _C1 , and the other terminal of this is connected to the input of the amplifier 21. and is grounded via a resistor 26 having a resistance value _R1 . The other terminal of the capacitor 25 is connected to one terminal of a capacitor 27 which also has a capacitance C ₂ , the other terminal of which is connected to the collector of an NPN transistor 28 , a switch which changes the impedance between the two states, and a resistor. It is connected via a resistor 29 having a value R ₃ to a bias terminal 30 which is biased by the power supply. The emitter of transistor 28 is grounded, and its base is connected to control terminal 31. By applying a predetermined voltage to this control terminal 31, the transistor 28 is activated.
It can be turned ON and OFF. Here, a circuit constituted by capacitors 25 and 27 and resistor 26 is impedance means including a reactance component, and constitutes a load of crystal resonator 24. That is, the Q value of the oscillator can be changed by turning the transistor 28 on and off. The resistor 29 is designed to have a value sufficiently larger than the resistance value of the load resistor 26 (R ₁ <<R ₃ ).
Moreover, when the transistor 28 is ON, that is,
When the VTR is playing, one terminal 2 of switch 23
3a becomes electrically conductive with the common terminal 23c, and when the transistor 28 is off, that is, when the VTR is recording, the other terminal 23b of the switch 23 is switched to electrically conductive with the common terminal 23c, so that the oscillation loop can be changed. It is configured.

In the crystal oscillator configured as above,
During playback, when a predetermined voltage is applied to the control terminal 31 to turn on the transistor 28, one terminal 23a of the switch 23 is brought into conduction with the common terminal 23c, forming an oscillator that does not pass through the phase shifter 22.
At this time, the load on the crystal oscillator 24 is C ₁ and Z =
R ₁ / (1 + ω ² C ² ₂ R ² ₁ ) + 1 / [jω {(1 + ω ² C ² ₂
R ² ₁ )/w ² C ₂ R ² ₁ }]. Here ω=2πf
and f is the frequency. For example, C ₁ =C ₂ =
When 27pF, R ₁ = 2KΩ and f = 4.43MHz, the resistance component is equivalently 0.6KΩ as shown in Figure 3a, and the capacitance component is 39pF and C ₁ are in series, so
It becomes 16pF. At this time, the transfer characteristic of the crystal resonator 24 becomes as indicated by 32 in FIG. 4, and it becomes possible to operate it as an oscillator with a high Q value.

If the crystal oscillator operated in this manner is used as the reference oscillator 5 shown in FIG. 1a, color signals during reproduction of a VTR can be processed in the same manner as in the prior art. Next, during recording, when the control terminal 31 is grounded and the transistor 28 is turned off, the other terminal 23b of the switch 23 is brought into conduction with the common terminal 23c, and a voltage controlled oscillator passing through the phase shifter 22 is configured. The load on the crystal oscillator 24 at this time is
Since R ₁ ≪ R ₃ , C ₁ =
27pF and R ₁ = 2KΩ, and the Q
The value will be lower than that when using the reference oscillator,
The phase characteristic changes over a wide range of frequencies, as shown at 35 in FIG. 5, compared to the characteristic 34 when the Q value is high. This voltage controlled oscillator is
When used as the voltage controlled oscillator 10 shown in FIG. b, it has the lock range necessary for a PLL, so it can process color signals during VTR recording in the same way as in the past.

Note that a resistor may be used instead of the capacitor 27 used in the above embodiment. In this case, by damping, the frequency that shows the peak value of the response characteristic in Figure 4 does not deviate much compared to the case without damping, but when using a capacitor, the frequency that shows the peak value shifts slightly due to damping, and the phase Characteristics also shift throughout.

Further, in the above embodiment, the NPN transistor 28 is used as a switch for switching the impedance between two states, but the switch is not limited to this, and other switches may also be used. can.

By the way, in the above explanation, the case where this invention is applied to a color signal processing circuit of a VTR has been described.
Needless to say, the present invention can also be used in other signal processing circuits.

As described in detail above, according to the present invention, the voltage-controlled phase shifter includes a filter constituted by a crystal resonator and an impedance means including a reactance component, an amplifier, and a voltage-controlled phase shifter. Since the crystal oscillator is configured so that it can be switched between non-passing and passing, a single crystal oscillator can be used to create a crystal oscillator with two functions: a reference oscillator and a voltage-controlled oscillator. This has the effect of reducing the cost of circuits to which this crystal oscillator can be applied.

[Brief explanation of the drawing]

Figure 1a shows a VTR using a conventional reference oscillator.
FIG. 1b is a block diagram of the color signal processing circuit during playback, FIG. Fig. 3b is a diagram showing the impedance in the other state, Fig. 4 is a diagram showing the response characteristics of an embodiment of the present invention, and Fig. 5 is its phase characteristic. FIG. In the figure, 21 is an amplifier, 22 is a voltage-controlled phase shifter, 23 is a changeover switch, 24 is a crystal resonator, 25 and 27 are capacitors, 26 and 29 are resistors, and 28 is a transistor. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A filter consisting of a crystal oscillator and impedance means including a reactance component, an amplifier with one end of the filter connected to the input end, and an output end of the amplifier connected to the input end. a voltage-controlled phase shifter, the first switching means for switchingly connecting the other end of the filter to the output terminal of the amplifier or the output terminal of the phase shifter; A crystal oscillator characterized in that a second switching means is provided for responsively switching the impedance value of the impedance means. 2 When the other end of the filter is connected to the phase shifter by the first switching means, the second switching means makes the impedance means high impedance, and the other end of the filter is connected to the amplifier by the first switching means. 2. The crystal oscillator according to claim 1, wherein the second switching means makes the impedance means low impedance.