JPH0212058B2 - - 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. Can not.

Therefore, voltage controlled oscillator circuits such as LC oscillators (or RC oscillators) have traditionally been used as voltage controlled oscillator circuits when a wide frequency change range is required. It was common practice to use a frequency converter to convert the low-frequency oscillation wave generated by the oscillation wave into a signal with a high frequency value. The disadvantage is that the oscillation frequency value changes greatly due to changes in the oscillation frequency, and the oscillation frequency value also changes significantly over time.

The present invention calibrates a normal 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 calibrates the voltage controlled oscillator as described above. During the period following the period in which the output of the voltage controlled oscillator is used for its intended purpose, the voltage controlled oscillator maintains the calibrated state during its calibration period and operates. This makes it possible to easily provide a voltage controlled oscillator circuit with high frequency stability.Hereinafter, the voltage controlled oscillator circuit of the present invention, that is, the output of the voltage controlled oscillator can be used for its original purpose. First and second signal switching means whose switching mode is changed according to a first period corresponding to all or part of the unused period and a second period other than the first period described above. And, in the first period mentioned above, the first period mentioned above is
The first reference voltage supplied via the signal switching means and the output signal voltage from the hold circuit are added together, and during the second period, the first reference voltage supplied via the first signal switching means is added. an adder that adds the external control voltage and the output signal voltage from the hold circuit; the output voltage of the adder is given as an oscillation frequency control voltage, and the oscillation frequency control voltage is a voltage controlled oscillator capable of outputting an oscillation wave of a predetermined frequency value in a state of a voltage value equal to a first reference voltage;
The voltage controlled oscillator has a frequency-voltage conversion characteristic such that an output voltage having a voltage value equal to the second reference voltage can be generated when the oscillation wave having the predetermined frequency value is supplied from the voltage controlled oscillator. The frequency at which the output signal of the voltage controlled oscillator is supplied -
a voltage converter; a voltage comparing means for comparing the output voltage of the frequency-voltage converter with a second reference voltage to generate a signal voltage corresponding to the voltage difference between the two voltages; During the period of
The output signal voltage of the voltage comparing means, which is supplied through the signal switching means, is applied as it is to the adder, and the voltage of the first period is compared at the time position immediately before switching to the second period. A specific example of a voltage controlled oscillator circuit comprising the aforementioned hold circuit which holds the output signal voltage of the means and continues to supply it to the adder during the second period, and which causes the aforementioned voltage controlled oscillator to output an output signal. The content will be explained in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of one embodiment of the voltage controlled oscillation circuit of the present invention. In this FIG. The control voltage from is applied to the fixed contact b of the changeover switch SW1. In addition, fixed contact c of changeover switch SW1
is given a voltage Vs1 from a reference voltage source VS1.

The movable contact a of the changeover switch SW1 receives the changeover control signal Sx applied from the changeover control signal supply terminal 2.
, the fixed contact b and the fixed contact c are switched. Each movable contact a in a changeover switch SW2, which will be described later, is also switched between a fixed contact b and a fixed contact c by a changeover control signal Sx applied from a changeover control signal supply terminal 3 to the changeover switch SW2.

The switching control signal Sx supplied to the switching control signal Sx supply terminals 2 and 3 in each of the switching switches SW1 and SW2 is a voltage controlled oscillator.
A first period in which the output So from the VCO is transmitted through the output terminal 4 corresponding to all or part of the period during which the output of the voltage controlled oscillator is not used for its original purpose, and a period other than the above-mentioned first period. A signal format may be used in which the level of the signal changes, for example, between a high level state and a low level state depending on the second period of the second period.

In addition, in Figure 1, each changeover switch SW
1.SW2 is shown as a mechanical changeover switch, but each changeover switch SW2 is shown as a mechanical changeover switch.
1. As SW2, a so-called electronic switch is used.

In the following explanation, each changeover switch SW1,
The switching control signal Sx that controls the switching operation of SW2 is in a high level state during a period (first period) corresponding to the entire period in which the output So from the voltage controlled oscillator VCO is not used for its original purpose. In addition, periods other than the above (second
period), the switching control signal is described as being at a low level.
When Sx is at low level, each movable contact a of each changeover switch SW1, SW2 is connected to fixed contact b.
When the switch is switched to the side and the switch control signal Sx is at a high level, each switch SW1,
Each movable contact a of SW2 is supposed to be switched to the fixed contact c side.

Movable contact a of changeover switch SW1 is adder ADD
(voltage adder ADD), and the other input terminal 6 of the adder ADD is connected to the output terminal 8 of the hold circuit HC, and the output of the adder ADD is a voltage controlled oscillator
Supplied as control voltage to VCO.

The hold circuit HC 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, the impedance on its input side is A device is used that has a function of storing the input voltage value to the terminal 7 immediately before switching from a low state to a high state and continuing to output that voltage value to the terminal 8. be.

Figure 2 shows a specific circuit example of the above-mentioned hold circuit HC. In Figure 2, 7 is an input terminal, 8 is an output terminal, FET is a field effect transistor, Ch is a storage capacitor, and R is a storage capacitor. The hold circuit HC shown in the second diagram is a storage capacitor that changes according to the input voltage value supplied to the input terminal 7 when the previous stage circuit connected to the input terminal 7 is in a low impedance state.
The terminal voltage of Ch is output to the output terminal 8 connected to the source of the field effect transistor FET,
In addition, when the pre-stage circuit connected to the input terminal 7 is disconnected by the changeover switch SW2 and the input terminal 7 is set to high impedance, immediately before the input terminal 7 is switched from low impedance to high impedance. The voltage value stored in the memory capacitor Ch is transferred to the field effect transistor.
The signal continues to be output from the FET source to the output terminal 8.

The output So of the voltage controlled oscillator VCO described above is sent to the output terminal 4 and is also given to the input terminal of the frequency discriminator DCT which operates as a frequency-voltage converter, and the output signal of the frequency discriminator DCT described above is Provided to the amplifier AMP.

The amplifier AMP described above can be used as an amplifier if the gain of the loop described later is large enough without using an amplifier.
Although the gain of the AMP may be small, the following description assumes that a differential amplifier is used as the amplifier AMP.

The output of the frequency discriminator DCT is applied to the non-inverting input terminal of the differential amplifier AMP, and the reference voltage Vs2 is applied from the reference voltage source VS2, and the output of the differential amplifier AMP is applied to the non-inverting input terminal of the differential amplifier AMP. The signal voltage corresponds to the difference voltage between the two input voltages, and the output of the differential amplifier AMP is supplied to the movable contact a of the changeover switch SW2.

The fixed contact c of the changeover switch SW2 is connected to the input terminal 7 of the hold circuit HC, and the fixed contact b of the changeover switch SW2 is left unconnected.

In the voltage controlled oscillator circuit of the present invention configured as described above, the output from the voltage controlled oscillator VCO
During the period when So is used for its original purpose, the switching control signal Sx applied to each changeover switch SW1, SW2 is in a low level state, and the movable contact a of each changeover switch SW1, SW2 is in a low level state.
is switched to the fixed contact b side (switched state as shown in FIG. 1).

In the above state, the voltage controlled oscillator VCO is
The control voltage from input terminal 1 is applied to one input terminal 5 of adder ADD via fixed contact b and movable contact a of changeover switch SW1, and the control voltage from input terminal 1 is applied to one input terminal 5 of adder ADD from hold circuit HC. An oscillation operation is performed using the voltage added to the correction voltage given to the control voltage as a control voltage, and the output So sent to the output terminal 4 is used for the desired purpose.

Next, when the switching control signal Sx is set to high level and the movable contacts a of each switch SW1 and SW2 are switched to the fixed contact c side, that is, when the output from the voltage controlled oscillator VCO is a period not used for (first period),
That is, the circuit operation during the calibration period for the voltage controlled oscillator VCO will be explained.

During the calibration period of the voltage controlled oscillator VCO, the movable contact a of each changeover switch SW1, SW2 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 5 of the adder ADD via the fixed contact c and the movable contact a of the changeover switch SW1. added to.
The output voltage of the hold circuit HC is given to the other input terminal 6 of the adder ADD, and therefore the voltage controlled oscillator is output as the output of the adder ADD.
The voltage supplied to the VCO as a control voltage is the sum of the reference voltage Vs1 of the reference voltage source VS1 and the output voltage of the hold circuit HC.

On the other hand, the output signal from the voltage controlled oscillator VCO is
The frequency discriminator DCT applies a voltage value corresponding to the frequency of the output signal from the voltage controlled oscillator VCO to the differential amplifier AMP.

The frequency discriminator DCT has a frequency-voltage conversion characteristic such that its frequency-voltage conversion characteristic is a reference frequency-voltage conversion characteristic, that is, its frequency -
Since the voltage conversion characteristics are predetermined, if the frequency of the output signal supplied from the voltage controlled oscillator VCO to the frequency discriminator DCT is fs, the input voltage applied to the inverting input terminal of the differential amplifier AMP is Vs2, and the output voltage of the differential amplifier AMP becomes zero.

However, 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 The voltage is different from the reference voltage Vs2, such as (Vs2+ΔV) or (Vs2−ΔV).

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 7 of the hold circuit HV via the movable contact a and the fixed contact c of the changeover switch SW2.

The hold circuit HC is the differential amplifier AMP mentioned above.
Since the output voltage of is supplied from the output terminal 8 to the input terminal 6 of the adder ADD, the voltage controlled oscillator
By changing the control voltage applied to the VCO, the voltage controlled oscillator VCO is controlled so that its oscillation frequency approaches fs.

In other words, adder ADD → voltage controlled oscillator VCO
→ Frequency discriminator DCT → Amplifier AMP → Movable contact a of changeover switch SW2 → Fixed contact c → Hold circuit HC → The loop of adder ADD forms a negative feedback path, so the loop gain is sufficiently large. In this case, 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 the voltage controlled oscillator VCO is held by the hold circuit HC, during the period (second period) during which the output of the voltage controlled oscillator VCO is used for its intended purpose following its calibration period, the voltage controlled oscillator VCO is Oscillation operation can be performed in a state where an output with a correct frequency value corresponding to the control voltage can be sent to the output terminal 4.

As is clear from the above explanation, in the voltage controlled oscillator circuit of the present invention, the period (first period) in which the output from the voltage controlled oscillator VCO is not used for its original purpose is used as the calibration period of the voltage controlled oscillator VCO. The voltage controlled oscillator VCO is calibrated so that the output signal of the voltage controlled oscillator circuit always has the correct frequency value during the second period when the output from the voltage controlled oscillator circuit is used for its intended purpose. It is possible to do so.

The period used for calibrating the voltage controlled oscillator VCO may be the entire period during which the output of the voltage controlled oscillator circuit is not used for its original purpose, but it is possible to use only a portion of that period. It's okay. 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.

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 number is directly oscillated by the voltage controlled oscillator.
This is because the frequency converter CONV1, which is required when a conventional voltage controlled oscillation circuit is used, is unnecessary. fc in FIGS. 3a and 3b represents a signal at the frequency of the low-pass conversion color subcarrier.

Note that if the signal processing circuit that uses the output from the voltage controlled oscillator circuit is, for example, a color TV signal processing circuit, the period during which the output from the voltage controlled oscillator is not used for its original purpose is the color Horizontal blanking periods in the 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, the voltage controlled oscillator circuit of the present invention is capable of stabilizing the frequency in a voltage controlled oscillator whose oscillation frequency is likely to change due to changes in temperature and humidity, and suppressing changes in the oscillation frequency over time. This can be easily prevented, and according to the present invention, all of the conventional problems mentioned above 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, ADD...Adder, HC...Hold circuit, VCO...Voltage controlled oscillator, DCT...Frequency discriminator, AMP→Amplifier, OSC...Oscillator, VS1, VS2...Reference voltage source.

Claims (1)

[Claims] 1. A switching mode according to a first period corresponding to all or part of the period in which the output of the voltage controlled oscillator is not used for its original purpose, and a second period other than the above-mentioned first period. and a first reference voltage supplied via the first signal switching means and the output signal voltage from the hold circuit during the first period. an adder that performs addition of the external control voltage supplied via the first signal switching means and the output signal voltage from the hold circuit during the second period; The output voltage of the adder is given as an oscillation frequency control voltage, and an oscillation wave of a predetermined frequency value can be output in a state where the oscillation frequency control voltage has a voltage value equal to the first reference voltage. A voltage controlled oscillator and a frequency-voltage conversion characteristic capable of generating an output voltage having a voltage value equal to the second reference voltage when the oscillation wave having the predetermined frequency value is supplied from the voltage controlled oscillator. a frequency-to-voltage converter comprising a frequency-to-voltage converter to which the output signal of the voltage-controlled oscillator described above is supplied, and a frequency-to-voltage converter as described above;
voltage comparison means for comparing the output voltage of the voltage converter with a second reference voltage and generating a signal voltage corresponding to the voltage difference between the two voltages; The output signal voltage of the above-mentioned voltage comparison means supplied via the signal switching means is directly applied to the above-mentioned adder, and the first signal voltage at the time position immediately before switching to the above-mentioned second period is
and the above-mentioned hold circuit that holds the output signal voltage of the voltage comparison means during the period and continues to supply it to the adder during the second period, and causes the voltage controlled oscillator to output the output signal. Controlled oscillation circuit.