JPH0337325B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic frequency control device for maintaining a carrier frequency in a frequency modulation system at a constant value. It was made so that it could be done.

In order to automatically control the carrier frequency in a conventional frequency modulation system, a frequency modulation wave signal is supplied to a frequency discrimination circuit, and the frequency is compared with a reference oscillation frequency.Based on the result, the carrier frequency oscillation is performed with a variable oscillation frequency. Since I was controlling the circuit, for example,
In order to transmit high-quality television signals by frequency modulating a carrier wave using a wideband television signal, it is necessary to use an extremely wideband and highly sensitive frequency discrimination circuit. The disadvantage is that the circuit device for automatic frequency control is complicated and expensive.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a relatively simple method that makes it possible to stably and highly accurately maintain the carrier frequency of a frequency modulated wave signal at a constant value by digitizing the circuit device. An object of the present invention is to provide an automatic frequency control device with a configuration.

That is, the automatic frequency control device of the present invention starts counting the wave number of the carrier wave in the frequency modulated wave signal every predetermined period, and sequentially generates a pulse signal having a pulse width equal to the time length required to count the predetermined wave number. a counter for counting the wave number of the corresponding reference frequency signal; a register for writing and temporarily holding the count output signal of the counter; and for sequentially converting the count output signal read from the register. A digital-to-analog converter for forming an analog signal is provided, and the analog signal is used as a frequency control signal.

The invention will be explained below by way of example embodiments with reference to the drawings.

First, an example of the configuration of the automatic frequency control device of the present invention is shown in FIG. 1, and signal waveforms of each part thereof are shown in FIG. 2.

In the automatic frequency control device having the configuration shown in FIG. 1, for example, when the carrier frequency of a modulated wave input signal frequency-modulated by a television signal is automatically controlled by the so-called keyed AFC method, the horizontal A reference synchronization input signal a having the same repetition frequency as a signal component with a constant repetition period included in a modulated wave input signal such as a synchronization signal is supplied to the gate pulse generation circuit 1 to generate a gate pulse b with an appropriate pulse width. The gate pulse b is generated synchronously and the gate pulse b is sent to the counter 2.
The portion where the carrier wave frequency of the modulated wave input signal is to be measured is periodically gated, and the wave number of the carrier wave included in that portion is counted. Note that in the case of the above-mentioned keyed AFC method, it is preferable to use the gate pulse b having the same pulse width in synchronization with the horizontal synchronization signal. In the counter 2, the wave number of the carrier wave is counted starting from the rising edge of the gate pulse b as shown in the waveform c in FIG. As shown in waveform d in the figure, a decoder output pulse is formed that rises at a count of 1 corresponding to the rise of gate pulse b and falls at a count of a certain number N that is appropriately set in relation to the pulse width of gate pulse b. . Therefore, the decoder output pulses d that are sequentially formed become a pulse train whose pulse width is modulated in response to the momentary change in the carrier wave frequency according to the frequency modulation of the modulated wave input signal.

In the configuration example shown in FIG. 1, in order to accurately and reliably measure the successive pulse widths of the above-mentioned pulse width modulated pulse train d, the pulse train d is applied to the counter 4, and the pulse width of the pulse train d is In order to obtain measurement accuracy sufficient to discriminate sequential changes in d in sequence, and the wave number of the reference signal wave in each successive gate period is counted as shown in the waveform e in FIG. The counting output of the counter 4 is sequentially supplied to the register 5, and the holding pulse g generated by supplying the reference synchronization input signal a to the hold pulse generation circuit 7 is applied to sequentially hold the counting output. , the held counting output signal level is sequentially converted into a DC voltage level by the digital-to-analog conversion circuit 6, thereby forming an analog signal f having signal levels sequentially corresponding to the sequential pulse widths of the pulse train d. This converted output analog signal has a signal level that sequentially corresponds to the carrier wave frequency of the modulated wave input signal, so if this converted output analog signal is used as an automatic frequency control signal, it will be extremely stable and highly accurate. Automatic frequency control can be performed.

Note that it is the modulated wave in the counter 2 that writes the count output of the counter 4 to the register 5 and temporarily holds it under the control of the hold pulse g from the hold pulse generation circuit 7 synchronized with the reference synchronization input signal a. Even if the rising position of each pulse in the pulse train d changes due to the relative phase relationship between the input signal and the gate pulse b, resulting in a state of being subjected to so-called pulse phase modulation, the signal level of the analog signal is prevented from changing accordingly. This is to make it happen.
In addition, the reset pulse h synchronously generated by the reset pulse generation circuit 8 to which the reference synchronization input signal a is applied is supplied to the counters 2 and 4, and the results of counting each carrier wave number described above are carried out every cycle of the reference synchronization signal. to prepare for the next wave number counting operation.

In the automatic frequency control device having the configuration shown in FIG. 1, a counter 2 and a decoder 3 are used to form a pulse width modulated pulse train d corresponding to changes in the carrier frequency of the modulated input signal, but the counting circuit itself It is also possible to directly form a pulse width modulation pulse train d which rises at the start of carrier wave number counting by application of gate pulse b and falls when the counting result reaches a predetermined value N.

In addition, in each of the above-mentioned configuration examples, the desired center frequency to be automatically controlled, that is, the so-called
The AFC frequency is set by changing the predetermined count value N in the counter 2 to change the average pulse width of the pulse width modulated pulse train d, and therefore the average DC signal level of the output analog signal f as an automatic frequency control signal. This can be done arbitrarily by letting the

As is clear from the above description, according to the present invention, highly accurate automatic frequency control is possible, and since the frequency control system of the automatic frequency control device can be digitized and configured with an integrated circuit, the frequency Stabilization of control circuit operation and cost reduction can be achieved, and the manufacturing cost of the automatic frequency control device can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the configuration of the automatic frequency control device of the present invention, and FIG. 2 is a waveform diagram showing signal waveforms at various parts thereof. 1... Gate pulse generation circuit, 2, 4... Counter, 3... Decoder, 5... Register, 6...
Digital-to-analog conversion circuit, 7...Hold pulse generation circuit, 8...Reset pulse generation circuit.

Claims (1)

[Claims] 1. A counting means that starts counting the wave number of a carrier wave in a frequency modulated wave signal every predetermined period and sequentially generates a pulse signal having a pulse width equal to the time length required to count the predetermined wave number, and the pulse signal a counter that counts the wave number of the reference frequency signal corresponding to the pulse width of the counter, a register that writes and temporarily holds the count output signal of the counter, and an analog signal that sequentially converts the count output signal read from the register. an automatic frequency control device, comprising: a digital-to-analog converter for forming a frequency control signal, the analog signal being a frequency control signal;