JPH0467834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a synchronization signal generation method for generating a signal synchronized with a horizontal synchronization signal of a television or the like.

[Prior Art] For example, in a printer that makes hard copies of televisions, when extracting a vertical synchronization signal, a signal synchronized with a horizontal synchronization signal is used.
In order to obtain this signal, conventionally, as shown in Fig. 4,
By using a phase-locked loop 13 consisting of a phase comparator 10, a low-pass filter 11, and a voltage-controlled oscillator 12 and supplying a horizontal synchronizing signal as an input signal, a signal synchronized with this signal can be obtained from the output of the voltage-controlled oscillator 12. There is.

However, the frequency of the horizontal synchronization signal is not constant, and varies depending on the model: 15.75KHz, 24KHz, or 32KHz. Therefore, in order to be able to synchronize with each frequency, range switching is performed using a resistor R, but this requires manual switching and can only be synchronized within a predetermined range.

Therefore, a device having the configuration shown in FIG. 5 was devised to automatically switch the range. This converts the frequency into a voltage by converting an input signal into pulses of a constant width using a one-shot pulse generator 14, and then integrating the pulses using an integrating circuit 15. Depending on this voltage level, the level detection circuit 1
A switching output is generated from 6, and the range switching circuit 1
7 switches the voltage of the voltage control circuit 12, and range switching is performed.

[Problems to be solved by the invention] In the latter conventional example, no measures are taken against temperature changes and secular changes, high stability is required for circuit components, and expensive components must be used. Ta. In addition, it was necessary to initially correct errors for each device due to variations in circuit components.

The present invention eliminates the above-mentioned drawbacks of the conventional technology by rewriting the frequency switching table at a predetermined timing such as when the power is turned on, thereby automatically correcting variations in circuit components, temperature changes, secular changes, etc. .

[Means for Solving the Problems] The present invention provides a memory circuit that stores control data specifying the frequency range of a voltage controlled oscillator constituting a phase-locked loop, and converts the control data from this memory circuit into a voltage. and a D/A converter that controls the frequency range of the voltage controlled oscillator, and at a predetermined timing such as when the power is turned on, control data is sequentially supplied to the D/A converter,
By measuring the output frequency (or period) of the voltage controlled oscillator when each control data is supplied and writing the control data to an address corresponding to the measurement result in the storage circuit, a table of control data is stored in the storage circuit. reads control data from the storage circuit according to the frequency (or period) of the input signal, controls the output voltage of the D/A converter using this control data, and adjusts the frequency range of the voltage controlled oscillator. It is designed to switch between.

[Embodiment] In FIG. 1, reference numeral 1 denotes a phase-locked loop, which includes a phase comparator 2, a low-pass filter 3, and a voltage-controlled oscillator 4. 5 is a voltage controlled oscillator 4
The D/A converter 6 switches the frequency range of the D/A converter 5, and 6 is a storage circuit composed of a RAM that stores a table of control data for the D/A converter 5. 7 is a selection circuit, 8 is an input signal period measurement circuit, 9 is a CPU,
This is a control circuit consisting of registers, accumulators, etc.

Next, the operation will be explained with reference to the flowcharts of FIGS. 2 and 3. First, the table creation operation of the memory circuit 6 will be explained with reference to FIG. This operation is performed at a predetermined timing, such as when the power is turned on, and in this example,
It is assumed that the control data consists of 8 bits. First, 255 is set as control data in the accumulator in the control circuit 9, and this is supplied to the D/A converter 5. Then, the selection circuit 7 selects the output of the voltage controlled oscillator 4, and the measurement circuit 8 measures the period of the output of the voltage controlled oscillator 4 whose range is specified by the output voltage from the D/A converter 5. be done. When this measurement timer counts up, the contents of the measurement circuit 8 are read into the control circuit 9, and the reciprocal thereof is taken and stored in a register. That is, the output frequency of the voltage controlled oscillator 4 is stored in the register. Then, N (255) is stored in the memory circuit 6 at the address indicated by the contents of the register.

Next, the contents of the accumulator are subtracted by one to 254, the same operation as above is performed, and 254 is stored at the address indicating the register at this time.

Thereafter, operations similar to those described above are repeated to create a table of control data in the storage circuit 6.

Next, the operation of generating a synchronization signal based on the above table will be explained with reference to FIG.
In this case, the selection circuit 7 is switched by the output of the control circuit 9, and an input signal such as a horizontal synchronization signal is supplied to the measurement circuit 8. When the period of this input signal is measured, its contents are read and its reciprocal, that is, the frequency of the input signal, is stored in a register. The control data at the address indicated by the register in the recording circuit 6 is loaded into the accumulator A and outputted to the D/A converter 5. Therefore, the control data according to the frequency of the input signal is transmitted to the D/A converter 5.
The voltage controlled oscillator 4 is automatically set to a range corresponding to the input signal.

Incidentally, since the control data table in the memory circuit 6 is rewritten each time the power is turned on, errors caused by secular changes in circuit components or temperature changes are automatically corrected, and an accurate table is always created.

Note that the timing for rewriting the table is not limited to when the power is turned on as described above, but may be rewritten at fixed intervals using a timer circuit. The rewriting may be performed at the location where the data is written.

Further, in the above embodiment, the period of the input is measured by the measuring circuit, but the frequency may be directly measured.

[Effects of the Invention] According to the present invention, the control data to the D/A converter is sequentially switched at a predetermined timing such as when the power is turned on, and the output frequency (or period) of the voltage controlled oscillator at that time is measured. By rewriting the contents of the memory circuit that stores the control data table, synchronization can be achieved automatically within a wide frequency range, and even if there are variations in parts for each device, errors caused by these can be corrected. , an optimal table can be created for each device even if inexpensive parts are used. Furthermore, errors due to aging and temperature changes are automatically corrected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are flowcharts for explaining the operation, and FIGS. 4 and 5 are block diagrams showing conventional circuit configurations. It is. DESCRIPTION OF SYMBOLS 1... Phase locked loop, 2... Phase comparator, 3... Low pass filter, 4... Voltage controlled oscillator, 5... D/A converter, 6... Memory circuit,
7... Selection circuit, 8... Measurement circuit, 9... Control circuit.

Claims (1)

[Claims] 1. A phase-locked loop consisting of a phase comparator, a low-pass filter, and a voltage-controlled oscillator, and a D/A conversion that receives control data and converts it into voltage to control the output frequency of the voltage-controlled oscillator. and a rewritable memory circuit for storing the control data, and outputs a synchronization signal synchronized with an input signal within a certain frequency range to the phase comparator from the voltage controlled oscillator. , At a predetermined timing such as when the power is turned on, the above D/
The control data supplied to the A converter is sequentially switched, the output frequency (or period) of the voltage controlled oscillator is measured at each switching time by a measurement circuit, and the control data is sent to an address corresponding to the measurement content at this time. By writing, control data for generating each frequency within the fixed frequency range from the voltage controlled oscillator is written in the storage circuit, the frequency (or period) of the input signal to the phase comparator is measured, and the The control data at the address corresponding to the measured value at the time is read from the memory circuit, this control data is supplied to the D/A converter, and the output frequency of the voltage controlled oscillator is adjusted to the input signal according to the output voltage. A synchronization signal generation method characterized by synchronization.