JPH04311160A - Sampling frequency control circuit - Google Patents

Abstract

PURPOSE:To converge reproduced sampling frequency information to required accuracy within a short time. CONSTITUTION:An image signal is sent from the transmitting side to the receiving side through a transmission line provided with a prescribed transmission frequency band. On the receiving side, receiving side frequency information is found out from the transmission line frequency and reproduced sampling frequency by the 1st frequency divider 14 and a counter 15 and an error between the transmitting side frequency information and the receiving side frequency information is found out by a subtractor 18 as frequency error information. A deviation between a previously determined convergent value and the frequency error information is found out by a forecasting device 20 and an adder 19 as a deviation value. The frequency error information is corrected in accordance with the deviation value to obtain corrected frequency error information. A voltage control oscillator 16 controls the reproduced sampling frequency in accordance with the corrected frequency error information.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sampling frequency control circuit, and more particularly to a sampling frequency control circuit for controlling a reproduction sampling frequency used in image reproduction.

0002

2. Description of the Related Art Generally, this type of sampling frequency control circuit reproduces reproduction sampling frequency information in accordance with transmitting side frequency information sent from the transmitting side. When transmitting an image signal, the image information is sampled on the transmitting side at a transmission sampling frequency to obtain an image signal, and the image signal is sent to the receiving side via a transmission line having a predetermined transmission line frequency. Then, on the receiving side, the image signal is reproduced using the reproduction sampling frequency. At this time, the transmitting side generates transmitting side frequency information based on the transmission line frequency and the transmitting sampling frequency, and the sampling frequency control circuit generates and controls the reproduction sampling frequency based on the transmission line frequency and the transmitting side frequency information. ing. Specifically, the sampling frequency control circuit obtains frequency error information based on transmission line frequency information and transmitting side frequency information, integrates this frequency error information, and determines the oscillation frequency of the voltage controlled oscillator based on the integrated value. is controlled to generate and control the reproduction sampling frequency information.

0003

[Problems to be Solved by the Invention] As mentioned above, in the conventional sampling frequency control circuit, reproduced sampling frequency information is obtained simply based on frequency error information. Since the oscillator is controlled, it often takes time for the reproduced sampling frequency information to converge to a desired accuracy.

An object of the present invention is to provide a sampling frequency control circuit that can converge reproduced sampling frequency information to a desired accuracy in a short time.

[0005]

[Means for Solving the Problems] According to the present invention, an image signal sampled at a transmission sampling frequency is received on a transmitting side via a transmission line having a predetermined transmission line frequency, and the image signal is sampled at a transmission sampling frequency at a reproduction sampling frequency. It is used when reproducing an image signal, and controls the reproduction sampling frequency based on transmission side frequency information generated on the transmission side based on the transmission path frequency and the transmission sampling frequency and sent from the transmission side. In the sampling frequency control circuit, a first generating means for obtaining receiving side frequency information based on the transmission path frequency and the reproduction sampling frequency, and determining an error between the transmitting side frequency information and the receiving side frequency information. The second frequency error information
and a generating means for determining a deviation between a predetermined convergence value and the frequency error information as a deviation amount based on the frequency error information, and correcting the frequency error information according to the deviation amount to generate a corrected frequency error. There is obtained a sampling frequency control circuit characterized in that it has a correction means for making information, and a control means for controlling the reproduced sampling frequency according to the corrected frequency error information.

[0006]

EXAMPLES The present invention will be explained below by way of examples.

Referring to FIG. 1, the illustrated sampling frequency control circuit is used to reproduce an image signal transmitted from a transmitting side. On the transmitting side (not shown), image information is sampled at a transmission sampling frequency to generate an image signal, and the image signal is sent to the receiving side via a transmission line having a predetermined transmission line frequency. On the receiving side, the image signal is reproduced based on reproduction sampling frequency information, which will be described later. Furthermore, on the transmitting side, transmitting side frequency information is generated based on the transmission path frequency and the transmitting sampling frequency,
Send to receiving side. The sampling frequency control circuit includes first and second input terminals 11 and 12 and an output terminal 13, receives the transmission line frequency as transmission line frequency information f1 at the first input terminal 11, and receives the transmission line frequency as transmission line frequency information f1. The transmitting side frequency information f2 is received at the input terminal 12 of the transmitter.

The transmission line frequency information f1 is transmitted to the first frequency divider 14.
The frequency is divided by a predetermined frequency division ratio M and inputted to the counter 15 as a first frequency division signal. Here, the frequency of the first frequency-divided signal (referred to as the first frequency-divided frequency) is, for example, 31.25 Hz.

Here, the oscillation frequency fSR of the frequency information (hereinafter referred to as reproduction sampling frequency information) output from the voltage controlled oscillator (VCO) 16 at the start of operation is 14
．． The frequency shall be 32MHz. This reproduction sampling frequency information is the second
is applied to the frequency divider 17, where the frequency is divided by a predetermined frequency division ratio N, and output as a second frequency divided signal. Here, N=
2, the frequency of the second divided signal is 7.16MHz
becomes.

This second frequency-divided signal is given to a counter 15, and the counter 15 calculates the frequency interval of the first frequency-divided signal,
That is, the number of pulses of the second frequency-divided signal is counted at intervals of 32 msec. Therefore, in this case, the counter 15 will output a count value of 229,120. This count value and the above-mentioned transmitting side frequency information are given to a subtracter 18, where the deviation between the transmitting side frequency information and the count value is determined and output as frequency error information. and,
This frequency error information is provided to an adder 19 and a predictor 20.

Referring now to FIG. 2, FIG. 2 shows the pull-in characteristic of the reproduced sampling frequency, with the horizontal axis representing time and the vertical axis representing the amount of deviation from the convergence value. Here, a straight line 101 represents a desired value (convergence value) at which the reproduction sampling frequency should converge, and a curve 102 represents the actual pull-in characteristic (convergence curve) of the reproduction sampling frequency. As is clear from FIG. 2, it can be seen that the convergence rate of the convergence curve (ΔNi/Δt, ΔNi represents a change in convergence value, and Δt represents a minute time) decreases as the amount of deviation decreases. In other words, it takes time for the convergence curve to converge. Furthermore, as is clear from FIG. 2, even if the initial deviation amount is large (or small), the convergence curve converges at approximately the same convergence rate from a predetermined point.

Therefore, the predictor 20 selects a predetermined point (
As shown in FIG. 2, the convergence rate is monitored by the predictor 20 from before point a. In other words, the predictor 20 monitors the convergence rate based on frequency error information (corresponding to the deviation amount), and when the convergence rate at the preset point a and the monitored convergence rate become the same, the actual convergence rate Predictor 20 will determine that the curve has reached point a. Since the deviation amount between point a and the convergence value can be calculated in advance, that is, the deviation amount between point a and the convergence value is set in the predictor 20 as the set deviation amount, and the predictor 20 calculates the monitoring convergence rate. a
When it is determined that the point has been reached, the set deviation amount is output.

The adder 19 adds the frequency error information and the set deviation amount to obtain added frequency error information. This added frequency error information is given to an integrator 21, where it is sequentially integrated and output as integrated frequency error information. Integral frequency error information is provided by digital-to-analog converter (D/A)
The signal is converted into an analog signal by the converter 22 and applied to the VCO 16. Then, the VCO 16 controls the oscillation frequency according to the analog signal and outputs it as reproduction sampling frequency information. This reproduced sampling frequency information is passed to the second frequency divider 17.
and output from the output terminal 13.

As described above, since the deviation amount is predicted by the predictor 20 and added to the frequency error information, it is possible to forcibly control the reproduced sampling frequency information to a converged value. In other words, the reproduced sampling frequency information can be instantly moved from point a in FIG. 2 to the predicted convergence value, and the convergence time can be significantly shortened.

[0015]

As explained above, in the present invention, the amount of deviation from a predetermined convergence position to a desired convergence value is obtained, this amount of deviation is added to frequency error information, and the reproduced sampling frequency is determined based on this added value. This has the effect of shortening the time required to bring the reproduced sampling frequency information to a desired convergence value.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of a sampling frequency control circuit according to the present invention.

FIG. 2 is a diagram showing an example of a pull-in characteristic of reproduced sampling frequency information.

[Explanation of symbols]

11 First input terminal 12 Second input terminal 13 Output terminal 14 First frequency divider 15 Counter 16 Voltage controlled oscillator (VCO) 17 Second frequency divider 18 Subtractor 19 Adder 20 Predictor 21 Integrator 22 D/A converter

Claims (2)

[Claims] 1. Used when receiving an image signal sampled at a transmission sampling frequency on a transmitting side via a transmission line having a predetermined transmission line frequency and reproducing the image signal at a reproduction sampling frequency, In the sampling frequency control circuit that controls the reproduction sampling frequency based on transmission side frequency information generated on the transmission side based on the transmission path frequency and the transmission sampling frequency and sent from the transmission side, the transmission path a first generating means for obtaining receiving side frequency information based on a frequency and the reproduction sampling frequency; and a second generating means for calculating an error between the transmitting side frequency information and the receiving side frequency information and generating frequency error information. Then, based on the frequency error information, a deviation between a predetermined convergence value and the frequency error information is determined as a deviation amount, and the frequency error information is corrected according to the deviation amount to obtain corrected frequency error information. A sampling frequency control circuit comprising: a correction means; and a control means for controlling the reproduced sampling frequency according to the corrected frequency error information. 2. The sampling frequency control circuit according to claim 1, wherein the correction means corrects the frequency error information when the rate of change over time of the frequency error information reaches a predetermined set rate of change. and the convergence value, and an addition means that adds the deviation amount to the frequency error information to obtain the corrected frequency error information. control circuit.