JPH0212059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has been made for the purpose of providing a voltage controlled oscillation circuit with good frequency stability.

As a voltage controlled oscillation circuit with high frequency stability, for example, a trimmer capacitor for frequency fine adjustment in a crystal oscillator is used as a variable capacitance diode,
A configuration in which a control voltage is supplied to the variable capacitance diode is conceivable, but since the voltage controlled oscillator circuit with this configuration has a very narrow frequency variable control range, it is necessary to have a wide frequency variable control range. It cannot be applied to purposes of use that are considered to be.

That is, for example, when processing a reproduced color TV video signal in a color VTR that records and reproduces a color television video signal (hereinafter referred to as "TV"), it is necessary to deal with fluctuations in the running speed of the magnetic tape. Sometimes a signal whose frequency value fluctuates is required, but since the above signal has a wide frequency variation range, it is not possible to use a voltage controlled oscillator circuit using a crystal oscillator to obtain such a signal. It cannot be done.

Therefore, voltage controlled oscillators such as LC oscillators (or RC oscillators) have traditionally been used as voltage controlled oscillator circuits when a wide range of frequency variation is required. It was common practice to use a frequency converter to convert a low frequency oscillation wave into a signal with a required high frequency value, but as is well known,
In the voltage controlled oscillator with the above configuration, the oscillation frequency value fluctuates greatly due to changes in temperature and humidity, etc.
The drawback was that the oscillation frequency value changed significantly over time.

The present invention calibrates a normal type voltage controlled oscillator whose frequency stability is not high, using all or part of the period during which the output thereof is not used for its original purpose as a calibration period, and following the calibration period of the voltage controlled oscillator described above. , during the period when the output of the voltage controlled oscillator is used for its original purpose, the voltage controlled oscillator operates while maintaining the calibrated state during its calibration period; calibrate the frequency discriminator used for the calibration of the voltage controlled oscillator during the calibration period of By maintaining the state during the calibration period of the voltage controlled oscillator, it is possible to easily provide a voltage controlled oscillation circuit with high frequency stability. The specific contents of the oscillation circuit will be explained in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of one embodiment of the voltage controlled oscillator circuit of the present invention. In this FIG. The control voltage from is applied to the fixed contact b of the changeover switch SW1. Further, a voltage Vs1 from a reference voltage source VS1 is applied to a fixed contact c of the changeover switch SW1. The movable contact a of the changeover switch SW1 is switched between a fixed contact b and a fixed contact c by a switching control signal Sx applied from a switching control signal supply terminal 2. Changeover switch SW described later
2. Each movable contact a in SW3 is also switched between fixed contact b and fixed contact c by a switching control signal Sx applied from switching control signal supply terminals 3 and 4 to each switching switch SW2 and SW3. .

The switching control signal Sx supplied to the switching control signal Sx supply terminals 2 to 4 in each of the switching switches SW1 to SW3 described above is a voltage controlled oscillator.
All or part of the period in which the output So from the VCO is used for its intended purpose via the output terminal 5, and the period in which the output So from the voltage controlled oscillator VCO is not used for its intended purpose. A signal format may be used in which the level of the signal changes, for example, between a low level state and a high level state during all or part of the period. In addition, in Fig. 1, each changeover switch SW1~
Although SW3 is shown as being a mechanical transfer switch, in practice, each of the transfer switches SW1-SW3 is a so-called electronic switch.

In the following explanation, each changeover switch SW1~
The switching control signal Sx that controls the switching operation of SW3 is
The output signal So from the voltage controlled oscillator VCO is at a low level during a period corresponding to the entire period when it is used for its original purpose.
In addition, it is described as being at a high level during periods other than the above, and when the switching control signal Sx is at a low level,
Each movable contact a of each switch SW1 to SW3 is switched to the fixed contact b side, and the switching control signal
When Sx is at a high level, each movable contact a of each switch SW1 to SW3 is switched to the fixed contact c side.

Movable contact a of changeover switch SW1 is adder ADD
1 (voltage adder ADD1), and the other input terminal 7 of the adder ADD1 mentioned above is connected to the output terminal 9 of the hold circuit HC1, and the output of the adder ADD1 is Supplied as a control voltage to the voltage controlled oscillator VCO.

The hold circuit HC1 described above is in a conductive state when its input side is driven in a low impedance state, and when its input side is driven in a high impedance state,
It is configured to have a function of storing the input voltage value to the terminal 8 immediately before the impedance on the input side switches from a low state to a high state and continuing to output that voltage value to the terminal 9. The same holds true for the hold circuit HC2, which will be described later.

Figure 2 shows the aforementioned hold circuits HC1 and HC2.
In Fig. 2, 8 is an input terminal, and 9 is an output terminal (the input and output terminals in the hold circuits HC1 and HC2 shown in Fig. 1).
In order to clarify the correspondence with FIG. 2, the output terminals are designated with the same reference numeral 8, and the input terminals are designated with the same symbol 8.
In addition, the output terminals are given the same symbol 9),
FET is a field effect transistor, Ch is a storage capacitor, and R is a resistor.The hold circuits HC1 and HC2 shown in the second diagram are connected to the input terminal 8 when the previous stage circuit connected to the input terminal 8 is in a low impedance state. The terminal voltage of the storage capacitor Ch, which changes according to the input voltage value supplied to the memory capacitor Ch, is output to the output terminal 9 connected to the source of the field effect transistor FET, and is also output to the input terminal 8.
The front stage circuit connected to is the changeover switch SW3.
When the input terminal 8 is disconnected by the input terminal 8 and the input terminal 8 becomes a high impedance, the voltage value stored in the storage capacitor Ch immediately before the input terminal 8 is switched from low impedance to high impedance is transferred to the field effect transistor FET. The signal continues to be output from the source to the output terminal 9.

The output So of the voltage controlled oscillator VCO mentioned above is sent to the output terminal 5 and is also sent to the changeover switch SW.
It is also supplied to the fixed contact c of No. 2. A reference oscillator OSC is connected to the fixed contact b of the changeover switch SW2, and an oscillator that can always output an output signal with a constant frequency value is used as the reference oscillator OSC, such as a crystal oscillator. may be done.

The movable contact a of the changeover switch SW2 is connected to the input terminal of a frequency discriminator DCT that operates as a frequency-voltage converter, and is connected to the input terminal of the frequency discriminator DCT, which operates as a frequency-voltage converter.
The output of DCT is output from adder ADD2 (voltage adder ADD
2) is applied to one input terminal 10. In addition, the other input terminal 11 of the adder ADD2 described above has
The output from the output terminal 9 of the hold circuit HC2 is supplied, and the output of the adder ADD2 is supplied to the amplifier.
Given to AMP.

It will be understood from the description below that the amplifier AMP described above may have any configuration as long as it has a sufficiently high degree of amplification, but in the following description, It is described as using a differential amplifier as the amplifier AMP.

The output of the adder ADD2 is applied to the non-inverting input terminal of the differential amplifier AMP.
A reference voltage Vs2 is given from a reference voltage source VS2, and the output of the differential amplifier AMP is set by a changeover switch.
It is supplied to the movable contact a of SW3.

The fixed contact c of the changeover switch SW3 is connected to the input terminal 8 of the hold circuit HC1, and the fixed contact b of the changeover switch SW3 is connected to the hold circuit HC1.
Connected to input terminal 8 of HC2.

In the voltage controlled oscillator circuit of the present invention configured as described above, during the period when the output So from the voltage controlled oscillator is used for its original purpose,
The switching control signal Sx applied to each switch SW1 to SW3 is set to a low level, and the movable contact a of each switch SW1 to SW3 is switched to the fixed contact b side (as shown in Fig. 1). In this state, the voltage controlled oscillator VCO outputs a signal from the input terminal 1 which is applied to one input terminal 6 of the adder ADD1 via the fixed contact b and the movable contact a of the changeover switch SW1. control voltage and adder from hold circuit HC1
The oscillation operation is performed using the voltage added to the correction voltage applied to the other input terminal 7 of ADD1 as the control voltage, and the output So is sent to the output terminal 5.
is used for the desired purpose, and the frequency discriminator DCT in said period also has a reference oscillator
The output of the OSC is input through the fixed contact b and the movable contact a of the changeover switch SW2, and the frequency discriminator is
A DCT calibration operation is performed.

Frequency discriminator performed during the above period
The calibration operation of the DCT is as follows. That is,
The frequency discriminator DCT receives an oscillation wave from the reference oscillator OSC which outputs an oscillation wave with a predetermined frequency value fs, and the frequency discriminator DCT outputs the output voltage of the voltage value corresponding to the frequency fs of the input signal to the frequency discriminator DCT. It goes without saying that the voltage value of the output voltage from the frequency discriminator DCT is determined by the frequency-voltage conversion characteristics of the frequency discriminator DCT. DCT
The frequency-voltage conversion characteristics of the device change with changes in temperature and humidity, and also change over time.

Now, suppose that when the frequency discriminator DCT has the standard frequency-voltage conversion characteristic and an input signal of frequency fs is given to it, the output voltage from the frequency discriminator DCT is Vs2. When an input signal with a frequency of fs is applied to the frequency discriminator DCT whose frequency-voltage conversion characteristics change due to changes in temperature or humidity or over time, the output voltage from the frequency discriminator DCT is Since its frequency-voltage conversion characteristic is different from the reference state described above, it exhibits a voltage value different from the output voltage value Vs2 in the reference state, such as (Vs2±ΔV).

Therefore, the reference voltage applied from the reference voltage source VS2 to the non-inverting input terminal of the differential amplifier AMP is
Output voltage value Vs2 obtained from frequency discriminator DCT when an input signal of frequency fs is given to frequency discriminator DCT having standard frequency-voltage conversion characteristics
If the frequency-voltage conversion characteristic of the frequency discriminator DCT deviates from the reference characteristic, the output voltage value output from the frequency discriminator DCT will deviate by +Δ or -ΔV with respect to the voltage value Vs2. Correspondingly, the differential amplifier AMP will output a large negative voltage or a large positive voltage.

The output of the differential amplifier AMP is switched to switch SW3.
is applied to the input terminal 8 of the hold circuit HC2 through the movable contact a and the fixed contact b, and from its output terminal 9, the output voltage of the differential amplifier AMP mentioned above is supplied to the other input terminal 11 of the adder ADD2. be done.

Since the differential amplifier AMP is configured as a negative feedback amplifier by the loop of adder ADD2 → differential amplifier AMP → movable contact a of changeover switch SW3 → fixed contact b → hold circuit HC2 → adder ADD2, differential By using an amplifier with a sufficiently high gain as the amplifier AMP, the voltage input from the adder ADD2 to the inverting input terminal of the differential amplifier AMP can be made approximately equal to the reference voltage Vs2.

That is, the output voltage Vs2 of the adder ADD2 in this state is the state in which a signal with a frequency value fs is given as an input signal to the frequency discriminator DCT when it has the standard frequency-voltage conversion characteristic. Therefore, the frequency discriminator DCT is calibrated by the above circuit operation. Since the calibrated state is held by the hold circuit HC2, the frequency discriminator DCT is controlled by the voltage controlled oscillator that follows during the calibration period for the frequency discriminator DCT.
During the calibration of the VCO, it will be advantageously used as a frequency discriminator DCT with reference frequency-to-voltage conversion characteristics for the calibration of the voltage controlled oscillator VCO, as described below.

Next, when the switching control signal Sx is set to high level and the movable contacts a of each switch SW1 to SW3 are switched to the fixed contact c side, that is, when the output from the voltage controlled oscillator VCO is The circuit operation during a period in which a calibration operation is performed on the voltage controlled oscillator VCO during a period when the voltage controlled oscillator VCO is not used will be described.

During the calibration period of the voltage controlled oscillator VCO, the movable contact a of each changeover switch SW1 to SW3 is switched to the fixed contact c side. By switching the movable contact a of the changeover switch SW1 to the fixed contact c, the reference voltage Vs1 of the reference voltage source VS1 is applied to one input terminal 6 of the adder ADD1 via the fixed contact c and the movable contact a of the changeover switch SW1. Added.
The output voltage of the hold circuit HC1 is given to the other input terminal 7 of the adder ADD1, and therefore, the voltage supplied as the control voltage to the voltage controlled oscillator VCO as the output of the adder ADD1 is based on the above-mentioned standard. This voltage is the sum of the reference voltage Vs1 of the voltage source VS1 and the output voltage of the hold circuit HC1.

On the other hand, the output signal from the voltage controlled oscillator VCO is
It is applied to the frequency discriminator DCT via the fixed contact c and the movable contact a of the changeover switch SW2, and from the frequency discriminator DCT, it is applied to the voltage controlled oscillator VCO described above.
An output voltage having a voltage value corresponding to the frequency of the output signal from one input terminal 1 of the adder ADD2
Added to 0.

The frequency discriminator DCT is the frequency discriminator described above.
The adder ADD is calibrated during the calibration period of the DCT and the frequency of the input signal to it is fs.
Since the output voltage of 2 is set to Vs2, the frequency of the output signal supplied from the voltage controlled oscillator VCO to the frequency discriminator DCT is fs
Then, the input voltage applied from the adder ADD2 to the inverting input terminal of the differential amplifier AMP becomes Vs2, and the output voltage of the differential amplifier AMP becomes zero.
If the frequency value of the output signal from the voltage controlled oscillator VCO deviates from the frequency fs by +Δfs or -Δfs, such as (fs±Δfs), the voltage input to the inverting input terminal of the differential amplifier AMP will be, for example, (Vs2+
ΔV) or Vs2−ΔV).
It will be different from 2.

As a result, the output voltage of the differential amplifier AMP becomes a large negative voltage or a large positive voltage, which is applied to the input terminal 8 of the hold circuit HC1 via the movable contact a and the fixed contact c of the changeover switch SW3.

The hold circuit HC1 is the differential amplifier described above.
AMP output voltage from output terminal 9 to adder ADD1
Since the control voltage applied to the voltage controlled oscillator VCO changes, the voltage controlled oscillator VCO is controlled so that its oscillation frequency approaches fs.

In other words, adder ADD1 → voltage controlled oscillator
VCO → Fixed contact c of changeover switch SW2 → Movable contact a → Frequency discriminator DCT → Adder ADD2 → Amplifier AMP → Movable contact a of changeover switch SW3 →
Fixed contact c → Hold circuit HC1 → Adder ADD
The loop No. 1 constitutes a negative feedback path, and therefore, if the loop gain is sufficiently large, the voltage controlled oscillator VCO is automatically controlled so that its oscillation frequency matches the frequency fs.

The results of the calibration for the voltage controlled oscillator VCO are:
Since it is held by the hold circuit HC1, the voltage controlled oscillator VCO is kept in the correct position according to the control voltage during the period when the output of the voltage controlled oscillator VCO is used for its intended purpose following its calibration period. Oscillation operation can be performed in a state where the output of the frequency value can be sent to the output terminal 5.

In this way, in the voltage controlled oscillator circuit of the present invention, the period when the output from the voltage controlled oscillator is not used (used) for its original purpose is set as the calibration period of the voltage controlled oscillator, and the voltage controlled oscillator is calibrated. During the period when the output from the voltage controlled oscillator is used for its original purpose, the frequency discriminator is calibrated during the period when the voltage controlled oscillator is calibrated. In this way, it is possible to ensure that the output signal of the voltage controlled oscillator always has the correct frequency value when the output from the voltage controlled oscillator is used for its intended purpose.

The period used for calibrating the voltage controlled oscillator may be the entire period during which the output of the voltage controlled oscillator is not used for its intended purpose, but it may be used for a portion of the period during which the output of the voltage controlled oscillator is not used for its intended purpose. Good too. However, since the above-mentioned calibration operation is performed by the operation of the negative feedback loop, the time length required for the negative feedback loop to exhibit a stable operating state is required as a calibration period.

Furthermore, the period used for calibrating the frequency discriminator may span the entire period during which the output of the voltage controlled oscillator is used for its original purpose, but it is also possible to use only a portion of that period. Good too. In this case as well, it goes without saying that the length of time required for the negative feedback loop operating for calibration to show stable operation is required as the calibration period.

Figure 3a shows the voltage controlled oscillation circuit of the present invention.
FIG. 2 is a block diagram showing an example of usage when used in an automatic phase control system in a VTR;
FIG. 3b is a block diagram of a conventional example shown for comparison.

In Figures 3a and 3b, OSCs is an oscillator that oscillates a signal at the frequency fsc of the color width carrier wave, BG is a burst gate, PC is a phase comparator, CONV1, CONV
2. CONV is a frequency converter, VCOa is a voltage controlled oscillator with a normal configuration, and VCOb is a voltage controlled oscillator circuit with a configuration as shown in the block diagram shown in FIG.

Comparing the circuit layout shown in FIG. 3a and the circuit layout shown in FIG. 3b, it is found that the circuit layout shown in FIG. Compared to the circuit arrangement shown in FIG. 3b, which is configured using an oscillation circuit, the number of frequency converters can be reduced by one, and the number of signal paths can be reduced by one block. The deterioration of S/N can be reduced. This is because the voltage controlled oscillator circuit of the present invention has high frequency stability, so the high frequency oscillation wave is directly oscillated by the voltage controlled oscillator circuit, and when a conventional voltage controlled oscillator circuit is used. This is because the frequency converter CONV1, which was required in the previous example, is no longer necessary. fc in FIGS. 3a and 3b represents a frequency signal of a low-pass conversion color width carrier wave.

Note that if the signal processing circuit that uses the output from the voltage controlled oscillation circuit is, for example, a color TV signal processing circuit, the period during which the output from the voltage controlled oscillation circuit is not used for its original purpose is:
A horizontal blanking interval in a color TV signal can be used.

It goes without saying that the voltage controlled oscillation circuit of the present invention can be used satisfactorily for signals other than TV signals, if a period during which the output from the voltage controlled oscillation circuit is not used can be set during signal processing.

As is clear from the above detailed explanation, in the voltage controlled oscillator circuit of the present invention, the voltage controlled oscillator of the normal type, which does not have high frequency stability, can be During the period during which the output of the voltage controlled oscillator is utilized for its intended purpose, following the voltage controlled oscillator calibration period, the voltage controlled oscillator is calibrated during its calibration period. In addition, the frequency discriminator used for calibrating the voltage controlled oscillator during the voltage controlled oscillator calibration period described above is also configured to operate while maintaining the voltage controlled oscillator's output. a period in which the output from the voltage controlled oscillator circuit is not used for its original purpose, such as calibration during all or part of the period during which it is used for
The calibration period of the voltage controlled oscillator and the calibration period of the frequency discriminator are set on the time axis by cleverly utilizing the other periods to calibrate the voltage controlled oscillator and the voltage controlled oscillator. Calibration of the frequency discriminator used is performed alternately on the time axis, and the center frequency of the voltage controlled oscillator is always set using the frequency discriminator in a state in which the frequency-voltage conversion characteristics are calibrated. The voltage controlled oscillators used in the construction of conventional voltage controlled oscillator circuits are used when a wide frequency variation range is required, i.e. due to changes in temperature or humidity, etc. Therefore, it is possible to easily provide a voltage controlled oscillator circuit with high frequency stability even when using a voltage controlled oscillator as a component, which has drawbacks such as large fluctuations in the oscillation frequency value and large changes over time in the oscillation frequency value. In addition, the stability of the center frequency of the voltage controlled oscillator in the voltage controlled oscillator circuit of the present invention is determined by the frequency -
This makes it possible to easily provide a voltage controlled oscillator circuit that has much better center frequency stability than that of a voltage controlled oscillator whose calibration is performed using a frequency discriminator whose voltage conversion characteristics are not calibrated. Accordingly, all of the above-mentioned conventional problems in voltage-controlled oscillation circuits in which the oscillation frequency can be variably controlled by a control voltage supplied from the outside can be satisfactorily solved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the voltage controlled oscillation circuit of the present invention, Fig. 2 is a circuit diagram of an example configuration of a hold circuit, and Figs. 3a and 3b are VTRs.
FIG. 2 is a block diagram of the automatic phase control system of FIG. SW1～SW2……Selector switch, ADD1,
ADD2...Adder, HC1, HC2...Hold circuit, VCO...Voltage controlled oscillator, DCT...Frequency discriminator, AMP...Amplifier, OSC...Reference oscillator, Vs1, Vs2...Reference voltage source.

Claims (1)

[Claims] 1. All or part of the period during which the output of the voltage controlled oscillator is not used for its original purpose is used as the calibration period of the voltage controlled oscillator, and the output of the voltage controlled oscillator is transferred to the voltage controlled oscillator via a negative feedback path including a frequency discriminator. means for calibrating the voltage controlled oscillator by feedback to the input side of the voltage controlled oscillator; means for maintaining the calibrated state during the calibration period; and means for maintaining the frequency discriminator during all or part of the period during which the output of the voltage controlled oscillator is utilized for its intended purpose. A means for calibrating the frequency discriminator by giving the output from the reference oscillator to the frequency discriminator as a calibration period, and a means for calibrating the frequency discriminator during the calibration period for the voltage controlled oscillator following the frequency discriminator calibration period described above. A voltage controlled oscillator circuit comprising: means for maintaining a calibrated state and operating during a calibration period of a frequency discriminator.