JPS6246337Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a local oscillation frequency control device for so-called synthesizer type frequency conversion, and in particular to a device that can extremely quickly, accurately and stably set local oscillation frequencies corresponding to a large number of reception frequencies over a wide range. It is. Conventional frequency conversion called the synthesizer method converts television radio frequency (RF) signals of all channels in the VHF band and UHF band, including positive and negative offset frequency signals for each channel, into a predetermined intermediate frequency signal. In this system, a large number of local oscillation frequencies corresponding to a large number of received frequencies are set by controlling the oscillation frequency of a voltage controlled oscillator using an applied voltage. This method is suitable when receiving text information signals that are multiplexed and broadcast during the vertical retrace period of a television video signal and processing them by synchronous detection because synchronous detection can be performed accurately and relatively quickly. Various circuit configurations are known as local oscillation frequency control devices using all-channel down converters for televisions that perform frequency conversion using the conventional original synthesizer method. In order to convert the radio waves of all channels of Jiyoung Broadcasting into intermediate wave signals, a large number of required local oscillation frequencies are generated by appropriately combining 18 types of fixed local oscillation frequencies and performing frequency synthesis. In such original local oscillation frequency synthesizers, it is necessary to use a large number of expensive crystal-controlled oscillators, and each required local oscillation frequency is generated by synthesizing a large number of fixed oscillation frequencies, so each local oscillation oscillation output signal The signal-to-noise ratio of the down converter deteriorates, increasing the overall noise figure of the down converter. Furthermore, in order to set a positive or negative offset frequency for each television channel, it is necessary to perform similar frequency synthesis by separately combining an oscillator with an offset frequency of about 10 KHz to the local oscillation frequency synthesizer described above. This causes an error equivalent to the offset frequency in the synthesizer's original local oscillation frequency, which causes a shift in the intermediate frequency selectivity characteristics that affect the performance of the intermediate frequency signal demodulator. When demodulating a frequency signal, there is a serious drawback in that the coherent detection reference carrier signal cannot be reproduced under the best conditions. In addition, as another example of a conventional synthesizer type oscillation frequency control device of this kind, a so-called synthesizer tuner used in FM and AM audio broadcast receivers receives step intervals corresponding to the local oscillation frequency original to the synthesizer type. In order to compensate for the offset or shift of the intermediate frequency that occurs when receiving a broadcast wave with an intermediate frequency, an oscillator with an oscillation frequency that adjusts the local oscillation frequency inherent to the synthesizer method is used separately. Some systems are designed to receive broadcast waves of intermediate frequencies that would otherwise be impossible to receive because the local oscillation frequencies inherent in the synthesizer system are arranged intermittently. Although it is possible to modify this method to receive television broadcasts, this method is difficult to use, for example, in a receiver that processes the reception of a teletext signal superimposed on a television signal or measures the transmission characteristics of a television signal. Quickly and easily generate the large number of local oscillator frequencies you need.
It has been difficult to generate them sequentially accurately and stably. That is, in a so-called synthesizer-type local oscillation frequency control device, for example, in order to shift the original local oscillation frequency corresponding to a television broadcast channel in accordance with an offset frequency, it is necessary to use an oscillator for the original local oscillation frequency and a reference frequency. It is necessary to have at least three oscillators, an oscillator and an offset frequency oscillator, and further,
Like television broadcast channels arranged in the 90-770 MHz range from the VHF band to the UHF band, a common oscillator generates a large number of local oscillation frequencies, each corresponding to a large number of reception frequencies arranged over a wide frequency range. In order to generate each signal starting from the oscillation frequency, the oscillation frequency of the common oscillator must be set to an extremely high frequency of several GHz, which is the least common multiple of the many local oscillation frequencies. The disadvantage is that the frequency accuracy required for such an extremely high oscillation frequency is extremely high. Further, as yet another example of a conventional local oscillation frequency control device of this type, in the circuit configuration shown in FIG. The oscillation output is converted into an intermediate frequency (IF) signal, and the local oscillation output is added to a programmable counter 5 controlled by a data input section 9 in which data for arithmetic processing corresponding to the frequency of each high-frequency signal is stored in advance. Then, the oscillation output of the voltage controlled oscillator corresponding to each high frequency signal frequency is subjected to necessary arithmetic processing and stepped down to a predetermined low phase comparison frequency. A compared signal waveform having a predetermined phase comparison frequency and a reference signal waveform having a predetermined phase comparison frequency formed by a reference oscillator 6 that oscillates at the same predetermined phase comparison frequency are connected to a phase comparison circuit 7, a phase determination circuit 8, and a counter 4. Control unit 1 consisting of
Supply to 0. The phase comparison circuit 7 compares the phases of the compared signal waveform and the reference signal waveform using a well-known method, and based on the signal level of the analog comparison output signal obtained as a result, the phase determination circuit 8 compares the compared signal waveforms. Leading phase signals or lagging signals representing the relative front and back of the phase of the and reference signal waveforms are respectively formed, and these leading or lagging signals are supplied to the counter 4 to calculate the leading or lagging signals. A digital control signal that is a digital value corresponding to the count value of the counter 4 is formed by adding or subtracting the number from the previous count value of the counter 4, and converts the digital control signal from digital to analog. The analog voltage signal is converted into an analog voltage signal by the voltage control oscillator 3, and then applied to the voltage controlled oscillator 2 to change its oscillation frequency. Therefore, in the local oscillation frequency control device having such a configuration, first of all, in the phase comparator 7,
In addition to performing analog phase comparison signal processing, a low-frequency filter whose cut-off frequency is sufficiently lower than the comparison frequency, that is, a long delay time, is used to smooth the output signal.
It is inadequate in terms of response characteristics, frequency stability, etc. Secondly, in order to be able to perform the phase comparison between the compared signal waveform and the reference signal waveform at a common phase comparison frequency for each of the local oscillation frequencies set in the intermittent array. In addition, it is necessary to set the phase comparison frequency to the minimum frequency difference between the local oscillation frequencies that are arranged and set intermittently. For example, by adding positive and negative offset frequencies to all television broadcast channels, In order to be able to commonly control each of the required local oscillation frequencies, the oscillation frequency of the oscillator that commonly generates these local oscillation frequencies must be as high as GHz as described above. Phase comparison frequency is at most equal to offset frequency
It is necessary to select an extremely low frequency of about 10KHz. Moreover, at the beginning of the phase comparison between the compared signal waveform and the reference signal waveform at the phase comparison frequency, for example, immediately after switching the reception channel, both the voltage controlled oscillator 2 and the reference oscillator 6 oscillate at an arbitrary phase. Moreover, the oscillation frequency of the voltage-controlled oscillator 2 changes because an appropriate control voltage is not yet applied to the oscillator 2 until the digital control signal described above reaches a predetermined value that usually differs for each receiving channel. , the frequency is not adjusted to the specified frequency. Therefore, an oscillation frequency signal that is slightly different from the predetermined frequency is stepped down, and phase comparison at a predetermined extremely low phase comparison frequency and correction control of the oscillation frequency based on the result of the phase comparison are repeatedly performed. As mentioned above, the phase comparison requires a long delay time, so a considerable time delay will occur until the oscillation frequency of the voltage controlled oscillator 2 matches the frequency that exactly corresponds to the newly switched receiving frequency. Become. For example, when it is necessary to quickly, accurately, and stably sequentially set the local oscillation frequencies corresponding to a large number of received frequencies, as in the measurement of the propagation characteristics of teletext radio waves mentioned above, this is simply impossible. There was a drawback. The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, and to set an extremely large number of local oscillation frequencies over a much wider frequency range compared to the frequency differences between them, each extremely quickly, accurately, and stably. It is an object of the present invention to provide a small and inexpensive local oscillation frequency control device that achieves the above-mentioned characteristics. That is, the local oscillation frequency control device of the present invention has the following characteristics:
A digital control signal according to the result of a phase comparison between a compared signal of a predetermined frequency, which is formed by stepping down the oscillation frequency of the local oscillation voltage controlled oscillator, and a reference signal of the predetermined frequency, which is formed by coupling to a reference oscillator. In the local oscillation frequency control device, the output square wave signal of the counter is successively delayed in small increments relative to the signal width in a local oscillation frequency control device that forms a signal, converts it from digital to analog, and applies it to the voltage controlled oscillator to control its oscillation frequency. a delay circuit that respectively forms the compared signal and the delayed output square wave signal with a square waveform; a reference counter that steps down the oscillation frequency of the reference oscillator to form the reference signal with a square waveform; and the compared signal. a reset pulse generating circuit for resetting the reference counter by generating a reset pulse having a timing corresponding to the leading edge of a square waveform; and a phase comparison between the compared signal and the reference signal by comparing the levels of the respective square waveforms. Therefore, there is provided a timing determination storage circuit that determines the context of each timing and stores the determination results, and controls the frequency step-down program of the counter and adapts the oscillation frequency of the voltage controlled oscillator to a desired receiving frequency. a control circuit that generates a control voltage of a certain value, corrects the value of the control voltage according to the determination result, and controls the reset pulse generation circuit to generate the reset pulse each time the correction is made; and the voltage control circuit. a digital data setting circuit that generates a digital control signal that makes the oscillation frequency of an oscillator correspond to the value of the control voltage; The timings of the trailing edges of each of the square waveforms are determined based on a combination of the compared signal, the reference signal, the delayed output square wave signal, and the reset pulse. It is characterized by: Hereinafter, the present invention will be described in detail with reference to the drawings. However, in the conventional device having the configuration shown in the first diagram described above, as a means of frequency comparison between the compared signal and the reference signal at a frequency much lower than the local oscillation frequency, phase comparison of the waveforms of both signals is performed. Since the oscillation frequency of the local oscillator is controlled in accordance with the result of the phase comparison, unnecessary phase comparison is performed at an extremely low comparison frequency for rough adjustment of the oscillation frequency of the local oscillator.
Precise control of the local oscillation frequency is performed by waiting until a phase lock state is reached in which both phases substantially match. Therefore, it has the disadvantage that it takes a considerable amount of time to set the required local oscillation frequency. The present invention improves this point, and makes the compared signal formed by the oscillation frequency down counter 5 in the conventional device into a square waveform with a duty ratio of 50%, for example, and also makes the oscillation frequency of the reference oscillator 6 proportional to the phase comparison frequency. Then, the reference oscillation frequency is stepped down by a counter in the same way as the compared signal side to form a reference signal having a square waveform with a duty ratio of 50%, and the local oscillation frequency immediately after switching the reception frequency is At the start of frequency control, the counter on the reference signal side is reset by a signal related to the compared signal to force the phases of the leading edges of the square waveforms of both the compared signal and the reference signal to match, and this phase lock is achieved. It is now possible to instantly compare the leading and lagging phases of the trailing edges of these rectangular waveforms. Furthermore, local oscillation of the output of the voltage controlled oscillator can be achieved by combining a configuration that roughly sets the voltage controlled oscillation frequency to a desired value and sets a step-down value of the voltage controlled oscillation frequency to the phase comparison frequency according to a predetermined program. This allows precise frequency control to be performed quickly. As a result, even when measuring radio wave propagation characteristics for an extremely large number of received frequencies by sequentially setting an extremely large number of local oscillation frequencies as described above, each local oscillation frequency can be set quickly and accurately. , character information signals can be reproduced in the best possible condition using the synchronous detection method. FIG. 2 shows a schematic configuration of the local oscillation frequency control device of the present invention that performs such operations. In the illustrated configuration, a voltage controlled oscillator 2 is controlled by a control voltage from a digital-to-analog converter 3, and its oscillation frequency is supplied to a programmable counter 5 to step down to the above-mentioned phase comparison frequency. The input radio frequency (RF) signal is converted into an intermediate frequency (IF) signal using the oscillation frequency as the local oscillation frequency. The compared signal formed by the programmable counter 5 compares the phase of the waveform with the reference signal in the frequency control section 11 shown surrounded by a dotted line as described below, and the phase advances based on the result of the phase comparison. , digital data corresponding to the slow phase is applied to the voltage controlled oscillator 2 as a control voltage via the digital data setting circuit 14, the digital-to-analog converter 3, etc. The frequency control unit 11 receives the output of the programmable counter 5 and the output of a reference frequency oscillator 6 such as a highly stable crystal oscillator, determines the timing relationship between the two input signals, and stores the result. A pulse timing judgment/holding circuit 12, a digital data setting circuit 14 which supplies a digital data signal to the digital-to-analog converter 3, and a data increase/decrease command signal are formed from the digital value output signal of the judgment/holding circuit 12. Processes signals from a data input unit 9 such as a keyboard that supplies signals to the setting circuit 14 and specifies channels, etc. In response to channel specification, sets general data for channels in the setting circuit 14 and generates a frequency control start signal. It is composed of a control circuit 13. Furthermore, the pulse timing judgment/holding circuit 12 judges the timing relationship between the comparison and reference input signals, and from the output holding the result, the control circuit 13 sets new settings in the digital data setting circuit 14. A command signal to increase or decrease the data to be set is generated and sent to the setting circuit 14, and in response to this command signal, the setting circuit 14 increases or decreases the previously set data by a predetermined value and resets the new data. do. This reset digital data is converted into an analog signal by a digital-to-analog converter 3 and applied to a voltage controlled oscillator to perform frequency control. In addition, if the oscillation frequency range of the voltage controlled oscillator is wide due to reasons such as spanning multiple reception bands, the circuit constants of the oscillation circuit etc. are changed according to a command from the control circuit 13 to adapt to the reception band. It is preferable to let Next, an example of the configuration of the device of the present invention showing the configuration of the frequency control section 11 in detail is shown in FIG.
A portion corresponding to the above-mentioned timing judgment holding circuit 12 is shown surrounded by a dashed line, and the timing judgment storage circuit 24, which is the main part thereof, is shown surrounded by a broken line, and the signal waveforms of each part are shown in FIG. show. The timing judgment holding circuit 12 in the illustrated configuration example receives the count output square wave signal Q of the programmable counter 5 with a duty ratio of 50%, for example.
The time τ is extremely small compared to the width of the square waveform.
₁ and τ ₂ to sequentially delay the first delayed output square wave signal Q _D1 and the second delayed output square wave signal Q
a delay circuit 16 that forms _D2 , and a reset pulse generation circuit 15 that generates a reset pulse at the timing of the rising edge of the first delayed output square wave signal _QD1 in response to a phase comparison start signal from the control circuit 13. Then, the oscillation output of the reference oscillator 6, which is set by the reset pulse and oscillates at a reference frequency set higher than the phase comparison frequency of, for example, about 10 KHz, is counted, and the frequency is stepped down to produce the aforementioned delayed output square wave. a reference counter 17 forming a counting output signal P having a square waveform with a leading edge matching the leading edge phase of the signal Q _D1 and a duty ratio of 50%;
The output signals of each circuit described above are supplied, and the trailing edge phases of the first delayed output square wave signal Q _D1 as the compared signal and the reference counter counting output square wave signal P as the reference signal are compared. , and a timing determination storage circuit 24 that determines and stores the timing relationship between the two. Therefore, in the timing judgment storage circuit 24, which constitutes the main part of the device of the present invention, the first delayed output square wave signal Q _D1 as the compared signal and the reference counter count output square wave signal P as the reference signal are exclusively used. The signal is supplied to the OR circuit 18 and the phases of the two are compared. Therefore, as described above, the reference counter 17 is reset by the reset pulse generated at the timing of the rising edge of the first delayed output square wave signal Q _D1 and starts counting down to the reference oscillation output frequency. Therefore, the leading edge of the counting output square wave signal P always rises simultaneously with the leading edge of the first delayed output square wave signal Q _D1 , and therefore, from the exclusive OR circuit 18, both Depending on whether the signal levels match or do not match near the trailing edge of the square wave signal, an exclusive OR output signal R of "0" or "1" is obtained as shown in FIG. Output signal R is supplied to latch circuits 19 and 20 in parallel. On the other hand, the gate signal generation circuit 21 provided in the timing judgment storage circuit 24 is supplied with the above-mentioned reset pulse and the second delayed output square wave signal _QD2 , and as shown in FIG. A gate signal G is formed which rises at the leading edge of the delayed output square wave signal Q _D1 and falls at the trailing edge of the second delayed output square wave signal Q _D2 . When this gate signal G is supplied in parallel to the NAND circuits 22 and 23, and the second delayed output square wave signal Q _D2 and the count output square wave signal Q of the counter 5 are supplied to the NAND circuits 22 and 23, respectively, As the NAND output signal, latch pulses are formed at the timing of the trailing edge of the gate signal G, that is, the trailing edge of the second delayed output square wave signal Q _D2 and the trailing edge of the count output square wave signal Q, and these latch pulses are latched. When applied to circuits 20 and 19 respectively, their latch circuits 19 and 2
0, the signal logic level of the exclusive OR output signal R at each latch timing is stored and held, as shown in FIG. 4, and the first and second latch output signals _Q1 and _Q2 are obtained, respectively. .
The latch circuits 19 and 20 are cleared by the above-mentioned reset pulse each time such phase comparison is started, and each time a new phase comparison result is stored and held. In the control circuit 13 which has supplied the first and second latch output signals Q ₁ and Q ₂ representing the results of the phase comparison between the compared signal and the reference signal as described above, the latch output signals Q ₁ , According to the interrelationship of the logical levels of Q ₂ , as shown in Table 1,
In order to form a new digital signal for controlling the increase or decrease of the oscillation frequency of the voltage controlled oscillator 2,
Forming and supplying a data increase/decrease command signal to the digital data setting circuit 14 via the control circuit 13;
For example, the digital data signal up to that point is increased or decreased by one unit. Therefore, at the same time as channel switching, the approximate oscillation frequency of the voltage controlled oscillator 2 generated based on the digital data signal of the setting circuit 14, which is roughly set according to the data from the data input section 9, is set as described above. By repeating phase comparison control, it is possible to precisely match the required local oscillation frequency.

[Table] In Table 1, Q ₁ =Q ₂ =0 indicates the state before the start of judgment, and Q ₁ =0, Q ₂ =1 or Q ₁
=1, Q ₂ =0 indicates that the oscillation frequency control digital data is increased or decreased according to the result of the phase comparison to perform a control operation that changes the oscillation frequency of the voltage controlled oscillator 2 up or down, and furthermore, such adjustment In order to start phase comparison again for a later new oscillation frequency, a phase comparison start signal is applied to the reset pulse generation circuit 15, and the reference counter 1
This shows that other circuits such as 7 are indirectly reset. Furthermore, since Q ₁ =Q ₂ =1 indicates a state in which the phase cannot be determined, a phase comparison start signal is applied to the reset pulse generating circuit 15 to try the phase comparison again. In addition, based on an operating principle similar to the above-described phase comparison between the compared signal and the reference signal, the length of the signal waveform length of the compared square wave signal at the phase comparison frequency is determined by comparing it with the time length of the reference. A square wavelength determination circuit is conventionally known which operates as shown in FIG. _5b with the configuration shown in FIG. The monostable multivibrator 25 is triggered at the rising edge, and its output square wave signal is supplied to the differentiating circuit 26 to generate a differential pulse at the trailing edge of the output square wave signal. The differential pulse generated after T ₁ and the input square wave signal e _i are supplied to the AND circuit 27, and a differential pulse e a corresponding only to the square waveforms P ₂ and P ₃ having a waveform length of T ₁ or more is generated _.
Take out. By triggering the monostable multivibrator 28 with this differential pulse e _a and supplying its output square wave signal to the differentiating circuit 29, a differential pulse e _p is generated after a certain period of time T ₂ has elapsed, and the differential pulse e When _p and the input square wave signal e _i are supplied to the AND circuit 31, the AND output signal is a long waveform detection output pulse e _L corresponding only to the square waveform P ₃ where the square wavelength T is T ₁ +T ₂ <T. The input square wave signal e which is obtained and whose polarity is inverted by the above-mentioned differential pulse e _p and the inverter 30 is
_i is supplied to the AND circuit 32, the square wavelength T is T ₁ <T<T ₁ +T ₂ as the AND output signal.
A short waveform detection output pulse e _S corresponding only to the square waveform P ₂ is obtained. Therefore, according to the conventional circuit shown in the figure, it is possible to determine the merits or demerits of the results of comparing each square wavelength T in the input square wave signal e _i with the reference time length (T ₁ +T ₂ ), and furthermore, the output A rectangular waveform having a waveform length T ₁ or more can be detected by the differential pulse e _p . However, in the conventional rectangular wavelength determination circuit described above, the entire range of time lengths that serve as the reference for waveform length determination is set by a combination of two monostable multivibrators; Not only is the configuration complicated, but the reference time length obtained by combining such analog time constant circuits is at least as good as the required performance, which the present invention aims to achieve, in terms of accuracy and stability. It was extremely difficult to obtain. In contrast, in the local oscillation frequency control device of the present invention, the above-mentioned reference time length is required by down-counting of a counter that resets the oscillation frequency of a fixed oscillator that stabilizes the reference square wave signal for phase comparison at the start of phase comparison. The delay time τ given on the comparison signal side is
₁ and _τ2 are minute compared to the comparison signal period,
Even if a normal delay circuit is used, sufficient accuracy can be maintained. Therefore, comparison and reference signals can be obtained with significantly higher accuracy and stability than in the conventional circuits described above. Furthermore, since the phase lead/lag judgment is all performed by digital signal processing, a relatively simple digital circuit configuration can provide much faster accuracy and reliability than in the past. Therefore, the local oscillation frequency control device of the present invention having the above-described configuration can be further improved in performance by appropriately modifying some of the functions of each circuit element such as the control circuit 13 and the digital data setting circuit 14. be able to. That is, for example, by specifying the channel number of the broadcast wave for which the local oscillation frequency is to be set, the offset frequency, and its presence or absence using the data input section 9, the digital data of the setting circuit 14 and the frequency down-down ratio in the counter 5 are set. After the oscillation frequency is roughly set, the voltage-controlled oscillation frequency control device is divided into a frequency adjustment period and a frequency measurement monitoring period. That is, during the frequency adjustment period, the oscillation frequency is roughly set to a desired value as specified by the data input section 9 as described above, and a state is made in which the phase comparison between the compared signal and the reference signal at the phase comparison frequency is possible. Therefore, the timing determination holding circuit 12 determines the relationship between the lead and lag of both phases, and based on the determination result, the numerical value of the digital data of the setting circuit 14 set in advance is set to ²
The value of X is increased or decreased in steps (X is an integer, and a step is one unit of digital data), and the value of X is decreased as the control adjustment is repeated. The value of this X is stored in the history of phase judgment, and the steps are sequentially decreased to X=2, 1, 0, i.e. 4, 2, 1 by reversing the phase judgment results of leading and lagging phases. do. By taking such measures, since the generally set oscillation frequency described above usually has a large deviation from the correct value, it is possible to increase the convergence speed of the control adjustment rather than performing the control adjustment one step at a time.
Next, during the frequency measurement monitoring period, after or even before the desired oscillation frequency is obtained with the required accuracy, relatively long-period disturbances such as fluctuations in ambient temperature and power supply voltage may cause Even if the oscillation frequency adjustment fluctuates, the required number of control adjustments are made based on the results of phase comparison, including the fluctuation, due to the same effect as described above. However, for this purpose, unlike the adjustment period, the phase The interval between comparison operations is widened to prevent the digital data of the setting circuit 14, that is, the control voltage level of the voltage controlled oscillator, from changing unnecessarily. That is, even with such intermittent frequency monitoring, the digital data setting circuit 14 that controls the increase/decrease of the oscillation frequency
The digital control circuits such as the above store the previous historical data unless new correction data is input, so it is possible to continuously maintain the adjusted state of the predetermined accuracy that has been reached for a while, and in such a state. Since the deviation in the oscillation frequency of the voltage controlled oscillator 2 is suppressed to the minimum possible range, the generation of spurious frequencies is also significantly reduced. Next, an application example of the local oscillation frequency control device of the present invention is shown in FIGS. 6 and 7, respectively. In the application example shown in FIG. 6, for example, a synchronous detection intermediate frequency demodulator 34 is connected in cascade to the device 33 of the present invention having the configuration shown in FIG. 3, and the input high frequency television signal is demodulated by the video signal. Since the device 33 of the present invention supplies an accurate intermediate frequency video signal to the synchronous detection demodulator 34 with an accuracy of, for example, within ±5 KHz for any channel of the input high frequency television signal, high precision is achieved. It is possible to perform synchronous detection according to predetermined characteristics, and the carrier wave for synchronous detection can also be reproduced in the best condition. In addition, in the application example shown in FIG. 7, a device 36 of the present invention is cascaded to the intermediate frequency modulation section 35 that supplies the video signal and the audio signal, for example, by replacing the input/output terminals in the configuration shown in FIG. By using the fact that the local oscillation frequencies generated by the device 36 of the present invention can be obtained with the required accuracy at intervals of about 10 KHz, which corresponds to the offset frequency of a television broadcast channel, for example, such an offset can be calculated. The radio waves of all channels of television broadcasting, including the radio waves, are generated with a predetermined frequency accuracy. As is clear from the above description, according to the present invention, the following remarkable effects can be obtained. (1) In an all-channel converter for television broadcasting, each required local oscillation frequency can be determined without frequency synthesis using a combination of multiple oscillators.
Each can be generated with a predetermined precision using only a single voltage controlled oscillator, and the signal-to-noise ratio of the local oscillation output signal accompanying frequency synthesis,
Therefore, an increase in the noise figure of the entire converter can be avoided. Moreover, the local oscillation frequency can be controlled with an accuracy of up to 5 digits using a programmable counter that steps down the oscillation frequency of the voltage controlled oscillator and converts it to the required phase comparison frequency. Even if an offset is applied to each television broadcast channel, the required frequencies of all channels can be generated and received with the required precision at frequency intervals of, for example, 10 KHz. (2) Oscillation frequency control of the voltage controlled oscillator based on the result of phase comparison between the compared signal and the reference signal at a phase comparison frequency that is a step down from the oscillation frequency of the voltage controlled oscillator for local oscillation. Since the application is performed by a digital circuit until immediately before application, the occurrence of jitter in the local oscillation frequency due to level fluctuations of the control voltage can be significantly reduced compared to the conventional method. (3) The use of a local oscillator mixer in conventional all-channel down converters for television broadcasting causes a degradation of the signal-to-noise ratio for the local oscillator frequency, thus increasing the noise figure of the entire converter. On the other hand, since the converter can be configured without using a local oscillation mixer, such deterioration of the signal-to-noise ratio and increase in the noise figure can be avoided. (4) The time required to compare the phase of the compared signal and the reference signal is much shorter than before, so even if a multi-digit frequency is specified, it will be within the allowable range in an extremely short time. can be accommodated in (5) As shown in Fig. 6, by combining the device of the present invention with a synchronous detection demodulator, it is possible to quickly, accurately and stably select a receiving channel for television broadcasting, and moreover, the local oscillation frequency can be Since it is possible to accurately set up to a large number of digits, the performance of the coherent detection demodulation section can be ensured at its best. (6) As shown in FIG. 7, by combining the device of the present invention with an intermediate frequency modulation section, the frequency accuracy of an all-channel modulator for television broadcasting can be improved with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional local oscillation frequency control device, FIG. 2 is a block diagram showing an example of a schematic configuration of the local oscillation frequency control device of the present invention, and FIG. 3 is a block diagram showing the detailed configuration. A block diagram showing an example, FIG. 4 is a waveform diagram showing signal waveforms of each part, and FIGS. 5a and b are block diagrams and waveform diagrams showing the configuration of a conventional rectangular wavelength determination circuit and signal waveforms of each part, respectively. , FIG. 6, and FIG. 7 are block diagrams showing examples of application of the device of the present invention, respectively. 1...Mixer circuit, 2...Voltage controlled oscillator, 3
... Digital-analog converter, 4 ... Counter, 5 ... Programmable counter, 6 ... Reference frequency oscillator, 7 ... Phase comparison circuit, 8 ... Phase determination circuit, 9 ... Data input section, 10, 11 ……
Control unit, 12... Timing judgment holding circuit, 13
...Control circuit, 14...Digital data setting circuit, 15...Reset pulse generation circuit, 16...
Delay circuit, 17... Counter, 18... Exclusive OR circuit, 19, 20... Latch circuit, 21... Gate signal generation circuit, 22, 23... NAND circuit,
24...timing judgment storage circuit, 25, 28...
... Monostable multivibrator, 26, 29 ... Differential circuit, 27, 31, 32 ... AND circuit, AND circuit, 30 ... Inverter, 33, 36 ... Device of the present invention, 34 ... Synchronous detection intermediate frequency demodulation Section, 35... Intermediate frequency modulation section.

Claims (1)

[Claims for Utility Model Registration] 1. A comparison signal of a predetermined frequency formed by stepping down the oscillation frequency of a local oscillation voltage controlled oscillator with a reference signal of the predetermined frequency formed by coupling it to a reference oscillator. In a local oscillation frequency control device that forms a digital control signal according to the result of phase comparison, converts it from digital to analog, and applies it to the voltage controlled oscillator to control its oscillation frequency, the output square wave signal of the counter is converted into a signal width. a delay circuit for sequentially delaying the comparison signal by a small amount relative to the reference signal to form the compared signal and the delayed output square wave signal, respectively, each having a square waveform; and forming the reference signal having a square waveform by stepping down the oscillation frequency of the reference oscillator. a reference counter that resets the reference counter; a reset pulse generation circuit that generates a reset pulse with a timing corresponding to the leading edge of the square waveform of the compared signal to reset the reference counter; and a timing determination memory circuit that determines the sequential relationship of each timing by phase comparison with the reference signal and stores the determination result; and a timing determination memory circuit that controls the frequency down program of the counter and oscillates the voltage controlled oscillator. Generating a control voltage having a value that adapts the frequency to the desired reception frequency, modifying the value of the control voltage according to the determination result, and controlling the reset pulse generating circuit to generate the reset pulse each time the modification is made. a digital data setting circuit that generates a digital control signal that makes the oscillation frequency of the voltage controlled oscillator correspond to the value of the control voltage, The timing of the trailing edge of each of the square waveforms is adjusted based on the combination of the compared signal, the reference signal, the delayed output square wave signal, and the reset pulse. A local oscillation frequency control device characterized by determining the context. 2 Utility Model Registration In the local oscillation frequency control device according to claim 1, the timing determination storage circuit is configured to include at least an exclusive OR circuit that supplies the compared signal and the reference signal, and an exclusive logic thereof. a pair of latch circuits that store the OR output signal of the summation circuit; and a gate that generates a gate pulse that rises at the leading edge of the square waveform of the compared signal and falls at the trailing edge of the delayed output square wave signal. and a pulse generating circuit, and drives the pair of latch circuits by respective NANDs of the gate pulse, the output square wave signal of the counter, and the delayed output square wave signal of the delay circuit. A local oscillation frequency control device characterized by: