JPS61281623A - Oscillation frequency adjusting device - Google Patents

Abstract

PURPOSE:To set accurately a free run frequency of the 1st VCO to a prescribed value by using a reference signal in a prescribed frequency to decide accurately the 2nd VCO oscillation frequency having nearly the same input/output characteristic as the 1st VCO used as the oscillation circuit and applying an error signal obtained in this way to the 1st VCO. CONSTITUTION:A reference signal generating circuit 18 generates, e.g., a signal of a frequency of 3.58MHz, a frequency divider 19 divides the frequency into 1/2 and the result is fed to a phase comparator 20. Further, the 1st and 2nd VCO 14, 16 generate a signal of 320fH (nearly 5MHz), the output of the VCO 16 is frequency-divided into 1/3 by the frequency divider 17 and fed to a phase comparator 20. An error signal obtained at an output terminal of the phase comparator 20 is fed to the VCO 14 and 16 via a low-pass filter 21 and each free run frequency is 5.4MHz. The free run frequency of the VCO 16 corresponds accurately to the reference signal from a reference signal generating circuit 18 because the VCO 16 is located in a PLL (phase locked loop and the free run frequency of the 1st VCO 14 corresponds accurately to the reference signal.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to an oscillation frequency adjustment device that can automatically adjust the IJ-run frequency of a VCO (Voltage Controlled Oscillator), and particularly relates to an oscillation frequency adjustment device that can automatically adjust the IJ-run frequency of a VCO (Voltage Controlled Oscillator). The present invention aims to provide an oscillation frequency adjustment device suitable for circuit implementation.

(b) Conventional technology In the color signal processing circuit of a VTR (video tape recorder), a first frequency conversion circuit converts a color subcarrier into a low-band converted color signal during recording, and a first frequency conversion circuit converts the low-band converted color signal into a low-band converted color signal during playback. A second frequency conversion circuit (which may be shared with the first frequency conversion circuit) for converting into a subcarrier is provided. , they are described in Figures 7-22 to 7-24 on pages 94 and 95 of ``rNHK Home Video Technology'' published by the Japan Broadcasting Publishing Association on November 10, 1981, for example. The frequency conversion circuit during recording has a configuration as shown in FIG. In FIG. 2, the 3.58 MHz color subcarrier applied to the input terminal (1) is transmitted from the main frequency conversion circuit (2) to the 4.2 MHz color subcarrier from the side frequency conversion circuit (3).
Mixed with MHz signal and output 629KH to output terminal (4)
A low frequency converted color signal of z is obtained. In addition, input terminal (5)
A horizontal synchronizing signal is applied to the horizontal synchronizing signal, and the horizontal synchronizing signal is waveform-shaped by a waveform shaping circuit (6).Then, the horizontal synchronizing signal is waveform-shaped by a waveform shaping circuit (6), and then outputted by a phase comparator circuit (7). The phase is compared with the V CO (81 is 160f
A signal of 1f, I is obtained at the output end of the oscillator having an oscillation frequency of II (approximately 2.5 MHz). The phase comparator (
The output signal of 7) is applied as an error signal to the V CO (81
Therefore, the oscillation frequency of the VCO (8) is exactly 16 Of. Further, the V CO (81
The output signal of 16 OfH is divided into 1/4 by the frequency divider (11) and applied to the sub frequency conversion circuit (3) via the phase shift circuit (11). This signal is 40f* ( 62
The frequency is 3,58 MHz generated from the oscillator (12+) in response to the color burst signal.
As a result, a 4°2 MHz signal is obtained at the output terminal of the sub frequency conversion circuit (3).

→ Problems to be solved by the invention As mentioned above, if the circuit shown in Fig. 2 is used, 3.58MHz
It is possible to convert the frequency of the color subcarrier of
When a resistor and a capacitor are created in the IC to determine the oscillation frequency of the VCO (81), the free-run frequency of the VCO (81) changes depending on the variation in the values of the resistor and cosidenser, and the frequency of the low-frequency conversion color signal also changes. Therefore, when converting to an IC, it is necessary to add an external pin to the IC, attach a variable resistor to the external pin, and adjust the value of the variable resistor. However, the increase in the number of external pins and external parts in the IC is not desirable, and some kind of improvement has been desired.

- Means for Solving the Problems The present invention has been made in view of the above points, and includes a first VCO whose oscillation frequency is controlled by a control signal, and a first VCO whose oscillation frequency is controlled by a control signal.
a second VCO having substantially the same input/output characteristics as the second VCO; a reference signal generating circuit that generates a reference signal of a predetermined frequency;
a comparison circuit that compares the phase of the output signal of the VCO and the reference signal to generate an error signal; and a comparison circuit that commonly supplies the error signal to the first and second VCOs to adjust the free run frequency of the first VCO. It is characterized by comprising a means.

(E) Effect According to the present invention, the error signal from the comparison circuit is output to the first VCO.
Since the free run frequency of the first VCO is accurately set according to the reference signal frequency,
The frequency of the output signal of the first VCO can be set to a value according to the control signal.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, where 0 is a control signal generation circuit that generates a control signal, (141 is a first VCO 1 to which the control signal is applied, and 151 is a first VCO 1 to which the control signal is applied). 1st VCO
A driven circuit to which the output signal of α4) is applied, (161 is a ZVCO having substantially the same input/output characteristics as the first VCO 141, and αη is a first frequency divider that divides the output signal of the second VCO (161) , aε is a reference signal generation circuit that generates a reference signal, (19 is a second frequency divider that divides the frequency of the reference signal, and () is the second VCO that compares the phase of the output signal of 161 and the reference signal. A phase comparison circuit that generates an error signal according to the phase difference, CII is a low-pass filter that passes the error signal, and CII is a signal line that supplies the error signal that has passed through the low-pass filter to the first and second VCOs α and αe. All of these are integrated on a single IC board.The reference signal generating circuit aS generates a signal having a frequency of, for example, 3.58 MHz, and the first signal is sent to the phase comparator (2). Also, the first and second V C0 (141 and H (16) C, 320
It generates a signal of fN (approximately 5 MHz), which is supplied to the phase comparator (2) by the first frequency divider αD. Therefore, the error signal obtained at the output terminal of the phase comparator
and (16), and the first and second VCO α4
The oscillation frequency of (161 and
141, the horizontal synchronizing signal and the output of the first VCO are applied as control signals, as in the case of FIG.
Becomes i.

Therefore, the free run frequency of the second VCO (1110) is determined by the fact that the vcoue is PLL (phase ψ locked).
Since the reference signal generation circuit is placed in the loop), it accurately corresponds to the reference signal from 0 seconds of the reference signal generation circuit, and the second VC
O (Resistor for determining the free run frequency of 161 -? Variations in the capacitor are absorbed. So, -C1 The first V However, since the degree of variation in the resistance and capacitor is naturally the same, the free run frequency of the first VCo (141) also corresponds accurately to the reference signal, and there is no need to manually adjust the free run frequency. Since the frequency of the reference signal is set sufficiently higher than the horizontal synchronization signal, the oscillation frequency of the first VCO (14) is determined predominantly by the stable reference signal, and the control signal corresponding to the horizontal synchronization signal is determined predominantly by the stable reference signal. are superimposed, making it easy to set the oscillation frequency of the first vCo (141) to a desired value.

Figure 3 shows a specific circuit example of the present invention.
An error signal supply circuit to which the error signal passed through the low-pass filter QIJ shown in FIG. ,C2? ) is a sum signal obtained by adding the output control signal of the control signal generation circuit U shown in FIG. The adder circuit that generates the addition signal is connected to the first
It is VCO.

When an error signal is applied to the input terminal @, a current corresponding to the error signal flows through the input transistor Gυ, is inverted by the current inverting circuit, and is then transferred from the collector of the first output transistor to the current source of the second VCO. Transistor (c) and (
goods) are supplied at the pace of supply. Therefore, the second v C0(
The oscillation frequency of 25+ will be in accordance with the error signal.Furthermore, the current in accordance with the error signal flowing through the input quadrant transistor υ is inverted in the current inverting circuit and then transferred to the second output transistor ( The control signal is supplied from the collector of the first VCOC to the first VCOC, and is added to the control signal applied to the input terminal (c) of the first VCOC and amplified by the differential amplifier circuit.
30.

Therefore, the oscillation frequency of the first VCO 2 corresponds to the addition signal of the error signal and the control signal.

The output signal obtained at the output terminal (to) of the second VCO is divided by the first frequency divider α in Figure 1, and then the phase comparator ■
n, the output terminal 6 of the first VcOfi? ) is supplied to the driven circuit f151 in FIG. Note that the first VCOi has the same circuit configuration as the second VCO (251), and the specific circuit is omitted in FIG. However, the present invention is not limited to this, and is applicable to various VCOs that are integrated.

(G1) Effects of the Invention As described above, according to the present invention, the second VCO which has substantially the same input/output characteristics as the first VCO used as an oversight circuit
The oscillation frequency of the second VCO is accurately shortened by the reference signal, and the resulting error signal is applied to the givco to automatically adjust the free run frequency of the 'igI VCO. It is possible to absorb variations in the elements during the process, and it is possible to set the free run frequency of the first VCO to a predetermined value. In particular, when the oscillation frequency of the first VCO is determined by the control signal and the error signal, if the frequency of the reference signal is set higher than the frequency of the control signal, it can be made more stable than the oscillation frequency t of the first VCO.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a frequency conversion circuit in a conventional VTR, and FIG. 3 is a circuit diagram showing a specific example of the circuit shown in FIG. It is. Explanation of main drawing numbers (141-@ IV CO, ttti・a 2 V
COl (181--Reference signal generation circuit, l...
Phase comparator, C! z...Signal line.

Claims (1)

[Claims] (1) First VC whose oscillation frequency is controlled by a control signal
O, a second VCO having substantially the same input/output characteristics as the first VCO;
CO, a reference signal generation circuit that generates a reference signal of a predetermined frequency, a comparison circuit that compares the phase of the output signal of the second VCO and the reference signal and generates an error signal, and a comparison circuit that generates an error signal by comparing the phase of the output signal of the second VCO with the reference signal, and a comparison circuit that generates an error signal. An oscillation frequency adjustment device comprising means for commonly supplying the error signal to adjust the free run frequency of the first VCO using the error signal.