JPH0681336B2 - Crystal voltage controlled oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a crystal voltage controlled oscillator, and in particular, a color signal having an original frequency of a low frequency conversion color signal reproduced in a magnetic recording / reproducing circuit of a VTR color video signal. The present invention relates to a crystal voltage controlled oscillator necessary for frequency conversion into.

[Conventional technology]

In a VTR, a color video signal is recorded by superimposing a color signal converted into a low frequency range, that is, a low frequency conversion color signal and a frequency-modulated luminance signal.

Therefore, during reproduction, the low-frequency conversion color signal is frequency-converted into the color signal of the original frequency. Also, during reproduction, time-axis fluctuations caused by the running system are included in the low-frequency conversion color signal as frequency fluctuation components.For this, the magnetic recording / reproducing circuit is equipped with an APC loop including a reference oscillator, When the frequency of the converted color signal is converted to the original frequency, the above frequency fluctuation component is canceled at the same time.

FIG. 2 is a block diagram showing an example of a conventional magnetic recording / reproducing circuit.

In FIG. 2, 1 is an automatic amplitude control circuit, 2 and 13 are frequency converters, 3 is a burst emphasis / de-emphasis circuit, 4 and 14 are bandpass filters, 5 are comb filters, and 6 is a crystal to which the present invention is applied. Voltage controlled oscillator, 7 and 15 burst gate circuit, 8 regenerative phase detector, 9 and 17 and 18 low pass filter, 10 addition circuit, 11 voltage controlled oscillator, 12 frequency divider and 16 recording phase Detector, 19 is an AFC circuit, SW1 to SW
6 is a switch.

During recording and reproduction, the switches SW1 to SW6 are switched to the R side and the P side, respectively, to control and process the signal flow between the blocks.

Next, the crystal voltage controlled oscillator 6 which is the object of the present invention will be described.

FIG. 3 is a circuit diagram showing an example of a conventional crystal voltage controlled oscillator 6.

This crystal voltage controlled oscillator operates as a voltage controlled oscillator that is synchronized with the burst signal of the input color signal during recording,
Also, during reproduction, it operates as a reference oscillator when converting the low-frequency converted color signal to the original frequency.

This crystal voltage controlled oscillator 6 is provided with first and second transistors Q ₁ and Q ₂ whose emitters are commonly connected, and receives a first reference voltage (V ₁ ) at a _first input end thereof and a second input end thereof. _A first differential amplifier 61 _A for differentially amplifying by inputting a first feedback signal (V _C ) to the first and second and _third transistors Q ₃ and Q ₄ commonly connecting emitters. The first feedback signal (V
A second differential amplifier 61 _B to enter the differential amplifier and the second feedback signal (V _I) to the second input terminal enter a _C), a second reference voltage source V2, the first end A first resistor R ₅ connected to the second reference voltage source V2 and a second end thereof connected to an input end of a recording phase detection signal input via a switch SW5, and a first end of the second reference voltage source The second resistor R ₆ connected to V 2 and the emitter are both connected to the output terminal (transistor Q ₁ and collector) in the opposite phase relationship with the second input terminal of the first differential amplifier 61 _A , and the bases thereof are respectively connected. The fifth and sixth transistors Q ₅ and Q ₆ , which are correspondingly connected to the second ends of the first and second resistors R ₅ and R ₆ , and the emitter are both connected to the second end of the second differential amplifier 61 _B. seventh及connecting to correspond to the second end of the input terminal and the second and the first resistor R ₆ output in-phase relationship connected-based (the collector of the transistor Q _3), respectively, R ₅ Transistor Q ₇ of the eighth,
The collector of Q ₈ and the sixth and the phase shift circuit 62 having a load resistor R ₇ to be connected to the collector of the eighth transistor Q _6, Q _8, transistor Q ₆ of the base 6 and 8, Q _8, and ninth transistor Q ₉ of emitter follower circuit connected, a third resistor R _8, the emitter of the first capacitor C _1, C ₂ and the crystal resonator X ₁ an input end comprising a ninth transistor Q ₉ a feedback circuit 63 to be connected, the connected between the fourth resistor R ₄ and a second end and a ground terminal of the fourth resistor R ₄ for connecting the first end and the output end of the feedback circuit 63 The second feedback signal (V _I ) is output from the first end of the _fourth resistor R ₄ and the first feedback signal (V _C ) is output from the second end of the _fourth resistor R ₄ with the second capacitor C _3. And a phase forming circuit 64 for outputting

Next, the operation of this crystal voltage controlled oscillator will be described.

If the respective voltages of the resistor R ₄ and the capacitor C ₃ of the phase forming circuit 64 are V _R and V _C , and their combined vector is V _I , the vector diagram is as shown in FIG.

The vector of V _R and V _C ′ (−V _C ) is input to the phase shift circuit 62, and the combined vector V ₀ appears at the emitter of the transistor Q ₉ , and the resistor R ₈ , the capacitors C ₁ and C ₂ and the crystal The oscillator X ₁ returns to the input terminal of the phase forming circuit 64 and oscillates at a frequency that matches V _I.

Since the switch SW5 is closed during recording, the recording phase detector 1
The output of 6 is converted to DC by the low-pass filter 17 and input to the bases of the transistors Q ₅ and Q ₈ as a recording phase detection signal.
Now the base voltage of the transistors Q ₅ and Q ₈ is the transistors Q ₆ and Q _7.
If it is lower than the base voltage of V _R , the combined vector of V _R and V _C ′ changes to V ₀ ′.

When the synthetic vector when the base bias voltage of the transistor Q ₅ to Q ₈ are equal to V _0, the phase change to match the V _I is the phase [Phi ₂ in V ₀ 'to the phase [Phi ₁ in V ₀ , The oscillation frequency changes and it operates as a voltage controlled oscillator.

On the other hand, since SW5 opens during playback, transistor Q
_Since the base voltages of _{5 to} Q ₈ are fixed and equal to each other, the composite vector V ₀ becomes constant and the reference oscillator operates as a constant frequency reference oscillator.

The resistors R ₅ and R ₆ are set to several tens of kΩ in consideration of the influence on the reduction filter 17.

[Problems to be Solved by the Invention]

In the above-described conventional crystal voltage controlled oscillator, since the values of the resistors R ₅ and R ₆ are set to 10 kΩ, a DC offset is generated in the phase shift circuit 62 by the transistors Q _{5 to} Q ₈ due to the mismatch of circuit elements. At the time of reproduction, even if the switch SW5 is open, the vector of the voltage V ₀ changes due to the offset and the oscillation frequency fluctuates, and the color signal that is frequency-converted and locked to the oscillation frequency of this crystal voltage controlled oscillator is input to the TV. If this is done, there is a drawback in that the color will not be attached because it deviates from the regular frequency.

Such a mismatch of circuit elements is an unavoidable problem even when integrated into an IC, and usually a circuit for adjusting this mismatch must be provided outside the IC. Therefore, the number of external parts and the number of adjustment steps are increased.

It is an object of the present invention to provide a crystal voltage controlled oscillator capable of suppressing variations in the oscillating frequency at the time of reproduction with a simple structure of an internal circuit and enabling no adjustment without being affected by the mismatch of circuit elements.

[Means for Solving the Problems]

A crystal voltage controlled oscillator according to the present invention includes first and second transistors whose emitters are commonly connected, and receives a first reference voltage at a first input terminal and a first feedback signal at a second input terminal. And a first differential amplifier for differential amplification, and third and fourth transistors whose emitters are commonly connected to each other. The first feedback signal is input to a first input terminal and a second input terminal is connected to a second input terminal. A second differential amplifier for inputting two feedback signals and performing differential amplification, a second reference voltage source, a first end connected to the second reference voltage source, and a second end connected to a recording phase detection signal. A first resistor connected to the input end, a second resistor connected to the second reference voltage source at the first end, and an emitter both having an opposite phase to the second input end of the first differential amplifier. A fifth and a fifth base connected to the output end of the base and the base respectively corresponding to the second ends of the first and second resistors. Both the transistor and the emitter of the second differential amplifier are connected to the output end of the second differential amplifier which is in phase with the second input end of the second differential amplifier, and the bases of the second differential amplifier are connected to the second ends of the second and first resistors, respectively. And 8th transistor, and a phase shifter circuit having a load resistance connected to the collectors of the 6th and 8th transistors, and an emitter follower circuit connecting the base to the collectors of the 6th and 8th transistors A ninth transistor, a third resistor, a first capacitor, and a crystal oscillator, a feedback circuit having an input end connected to the emitter of the ninth transistor, and a first end serving as an output end of the feedback circuit. A fourth resistor to be connected and a second capacitor connected between the second end of the fourth resistor and the ground terminal are provided, and the second feedback signal is output from the first end of the fourth resistor. Shisai said The first of the resistance 2
A crystal voltage controlled oscillator having a phase forming circuit that outputs the first feedback signal from an end, the first and second
10th and 11th transistors for switching, in which the emitter and the collector are oppositely connected in parallel and the bases are connected in common, are provided between the second ends of the resistors of, and recorded in the bases of these 10th and 11th transistors. Sometimes these tenth
And a voltage that turns on the eleventh transistor and turns on during reproduction.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

This embodiment differs from the conventional crystal voltage controlled oscillator shown in FIG. 3 in that the emitter and the collector are opposite to each other between the second ends of the first and second resistors R ₅ and R ₆ . parallel connecting Te, the transistors Q _10, Q ₁₁ for switching which is connected in common base is provided with respect to the voltage V ₂ of the reference voltage source V2 is provided a voltage source V4 of the voltage source V3 and the voltage V ₄ of the voltage V ₃ V ₃ > V ₂
Set each voltage so that> V ₄ and turn on the transistors Q ₁₀ and Q.
_{The point} is that voltages V ₃ and V ₄ are applied to the base of ₁₁ through a switch SW so that these transistors Q ₁₀ and Q ₁₁ are turned off during recording and turned on during reproduction.

Next, the operation of this embodiment will be described.

Since each voltage V _{2 to} V ₄ is V ₃ > V ₂ > V ₄ , transistors Q ₁₀ and Q ₁₁ are turned off during recording, and this crystal voltage controlled oscillator is input via switch SW 5 While the voltage controlled oscillator by the phase detection signal, the transistors Q _10, Q ₁₁ are turned on at the time of reproducing base bias voltage of the transistor Q ₅ to Q ₈ are matched, to remove the offset due to mismatch of the circuit elements Since the vector of V ₀ is always constant, it is possible to suppress variations in the oscillation frequency.

〔The invention's effect〕

As described above, according to the present invention, two switching transistors in which the emitter and the collector are oppositely connected in parallel are provided between the second ends of the first and second resistors, and these transistors are in an off state during recording. In addition, by adopting a configuration in which it is turned on at the time of reproduction, it is possible to suppress variation in the oscillation frequency at the time of reproduction due to a mismatch of circuit elements with a simple circuit configuration, and to make adjustment unnecessary.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a magnetic recording / reproducing circuit to which a conventional crystal voltage control oscillator is applied, and FIG. 3 is a conventional crystal voltage control circuit. FIG. 4 is a circuit diagram showing an example, and FIG. 4 is a vector diagram of signals of respective parts for explaining the operation of the crystal voltage controlled oscillator shown in FIG. 6 ... Crystal voltage controlled oscillator, 13 ... Frequency converter, 16 ...
… Recording phase detector, 17 …… Low-pass filter, 61 _A , 61 _B ……
Differential amplifier, 62 ... Phase shift circuit, 63 ... Feedback circuit, 64 ...
Phase forming circuit, C _{1 to} C ₃ ... Capacitor, Q _{1 to} Q ₁₁ ... Transistor, R _{1 to} R ₈ ... Resistor, S1 to S3 ... Current source, SW, S
W1~SW6 ...... switch, V1~V4 ...... voltage source, X ₁ ...... crystal oscillator.

Claims (1)

[Claims] 1. A differential circuit comprising first and second transistors having emitters commonly connected to each other, wherein a first reference voltage is input to a first input terminal and a first feedback signal is input to a second input terminal. A first differential amplifier for amplifying, and a third and a fourth transistor whose emitters are commonly connected, the first feedback signal is input to a first input end, and a second feedback signal is input to a second input end. A second differential amplifier for inputting and differentially amplifying, a second reference voltage source, a first end connected to the second reference voltage source, and a second end connected to an input end of a recording phase detection signal. A first resistor, a second resistor whose first end is connected to the second reference voltage source, and an emitter whose output is in an opposite phase relationship with the second input end of the first differential amplifier. Fifth and sixth terminals connected to the bases respectively corresponding to the second ends of the first and second resistors.
Both the transistor and the emitter of the second differential amplifier are connected to the output end of the second differential amplifier, which is in phase with the second input end, and the bases of the second differential amplifier are connected to the second ends of the second and first resistors, respectively. And 8th transistor, and a phase shifter circuit having a load resistance connected to the collectors of the 6th and 8th transistors, and an emitter follower circuit connecting the base to the collectors of the 6th and 8th transistors A ninth transistor, a third resistor, a first capacitor, and a crystal oscillator, and a feedback circuit having an input end connected to the emitter of the ninth transistor, and a first end serving as an output end of the feedback circuit. A fourth resistor to be connected and a second capacitor connected between the second end of the fourth resistor and the ground terminal are provided, and the second feedback signal is output from the first end of the fourth resistor. The fourth A crystal voltage controlled oscillator having a phase forming circuit for outputting the first feedback signal from a second end of a resistor, wherein an emitter and a collector are opposite to each other between second ends of the first and second resistors. Providing switching 10th and 11th transistors connected in parallel and having their bases connected in common, the 10th and 11th transistors are turned off during recording on the bases of these 10th and 11th transistors, and turned on during playback. A crystal voltage controlled oscillator characterized in that a voltage to be applied is applied.