JPH03247090A - Sampling frequency control system - Google Patents

Abstract

PURPOSE:To reproduce a sampling frequency accurately without being affected with an error included in frequency information by providing a means correcting a frequency difference so as to make a reproduction side sampling frequency equal to a sampling frequency of a sender side. CONSTITUTION:A means correcting a frequency difference consists of an elastic storage 7, a selector 8 and an adder 9 and monitors a phase difference of a write/read pointer of an elastic storage ES 7 storing tentatively a sent data, that is, the residual quantity of the memory in the inside of the ES 7 and sends the information to the selector 8. Thus, a correction value +alpha is selected by the selector 8 to output the data in the inside of the ES 7 quickly to increase the voltage of a VCO 12 positively thereby increasing the sampling frequency of the VCO 12. If a reference phase difference is too close, the correction value -alphais selected to decrease the voltage of the VCO 12 negatively thereby decreasing the sampling frequency. When the phase difference is within reference phase difference + or - L sample, the correction value 0 is selected to make the sampling frequency unchanged. Thus, the sampling frequency at the sender side is made equal to the sampling frequency at the reproduction side.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sampling frequency control method for an image encoding device that transmits and reproduces frequency information sampled in synchronization with an input image.

(Prior Art) In the frequency control method of a conventional two-image encoding device, a difference in frequency information between frequency information transmitted from a transmitting side and reproduced frequency information reproduced on a reproducing side is extracted and integrated by an integrator. Furthermore, the value output by this integrator is converted into an analog value by a digital-to-analog converter, and this analog value controls a voltage-controlled crystal oscillator (hereinafter referred to as VCO) to output a reproduction sampling frequency. I was doing it.

(Problems to be Solved by the Invention) In the conventional system described above, the voltage of the VCO is controlled so that the frequency information on the reproduction side and the transmission side match, or when the two frequency information contains an error, the reproduction is stopped. It was not possible to match the sampling frequency and the sampling frequency on the transmitting side.

An object of the present invention is to provide a sampling frequency control method that can accurately reproduce a sampling frequency without being affected by errors included in one frequency information.

(Means for Solving the Problems) The present invention provides an apparatus for reproducing an image signal transmitted via a digital communication circuit operating at a transmission line frequency fL at a reproduction sampling frequency fSR.
A first frequency divider that divides L into 1/M, a second frequency divider that divides the reproduced sampling frequency fSR into 1/N, and a frequency divided by the first frequency divider. the second frequency with a period of the frequency
A reproduction side counter that counts the frequency divided by the frequency divider, and a frequency that is obtained by dividing the transmission sampling frequency fSS by 1/N at the frequency interval obtained by dividing the transmission line frequency fL by 1/M on the transmitting side. a subtracter that calculates the difference between the frequency information on the transmitting side counted and sent by the counter on the transmitting side and the frequency information counted by the counter on the reproducing side;

means for temporarily storing the transmitted data and correcting the output of the subtracter according to the phase difference between writing and reading of the stored data; an integrator for integrating the value output from the correction means; A digital-to-analog converter converts the value output from the integrator into a digital-to-analog converter, and a voltage-controlled crystal oscillator oscillates the reproduction sampling frequency fSR using the value output from the digital-to-analog converter. Features.

Note that the correction means sets one of a plurality of values predetermined according to the phase difference between the elastic store that temporarily stores the transmitted data and the write/read pointer of the elastic store. It consists of a selector that selects and outputs it, and an adder that adds the frequency information difference output from the subtracter and the value output from the selector.

(Example) An embodiment of the present invention will be described with reference to one drawing.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In Figure 1, the transmission line frequency f that is manually input from terminal 1
The first frequency divider 3 divides L at a predetermined frequency division ratio M. -As an example.

The frequency after being divided by frequency divider 3 is 31.25MH
Assume that z.

Assuming that the frequency fSR output from the voltage controlled crystal oscillator (hereinafter referred to as VCO) 12 that generates the reproduction sampling frequency fSR on the reproduction side is 14.32M1lz, the frequency oscillated by the VCO 12 is divided into the second fraction. A frequency divider 4 divides the frequency at a predetermined frequency division ratio N. When the frequency division ratio is N=2, the counter 5 counts the period of the frequency divided by the frequency divider 3, that is, the number of clocks output from the frequency divider 4 at intervals of 32 msec. In this case, the numerical value per unit time output from the counter 5 is 229120.

Similarly, the frequency information counted by the transmitting side counter is input to the subtracter 6 through the terminal 2.

A subtracter 6 calculates the difference between the frequency information counted on the transmitting side and the frequency information counted by the counter 5 on the reproducing side.

The present invention includes means for correcting the frequency difference extracted as described above. This correction means includes an elastic store 7, a selector 8. The phase difference between the write/read pointer of the elastic store 7 (hereinafter referred to as SE), which consists of an adder 9 and temporarily stores transmitted data.

Monitors the remaining amount of memory inside the ES7 and sends the information to the selector 8.

As an example, when the reference phase difference of ES7 is longer than the reference phase difference by L samples or more, the following operation is performed to return to the reference phase difference. That is, in order to quickly output the data inside the ES 7, the selector 8 selects the correction value 0α, increases the voltage of the VCO 12 to the + side, and increases the sampling frequency of the VCO 12.

If the reference phase difference is too close, select the correction value -α.

Lower the voltage of VCO 12 to one side to reduce the sampling frequency. Also, if the reference phase difference is within ±L samples, the correction value is 0.
Select and do not change the sampling frequency.

Next, the adder 9 adds the correction value output from the selector 8 to the frequency information difference output from the subtracter 6 to perform correction.

The information output from the adder 9 is input to the integrator 10,
The integrated information is fed into a digital-to-analog converter 11. The information converted to this analog value is
The oscillation frequency of the VCO 12 is controlled to change the frequency. The oscillated reproduction sampling frequency fSR is output to the terminal 13 and also to the frequency divider 4.

If you do this, if the reproduction sampling frequency does not match the sampling frequency on the transmitting side due to an error in the frequency information, the phase difference detected by ES7 will be blurred, so the phase difference detected by ES7 will be By adding correction to the frequency information accordingly, the sampling frequency on the reproducing side is voltage controlled by the VCO 12 to match the sampling frequency on the transmitting side.

By repeating this, it is possible to match the sampling frequency on the transmitting side and the reproduction sampling frequency.

(Effects of the Invention) As explained above, the present invention provides an image decoding device that transmits and reproduces frequency information sampled in synchronization with an input image. Even if an error is included, the sampling frequency on the reproducing side can be made to match the sampling frequency on the transmitting side.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. 2... Transmission side frequency information input terminal, 3, 4... Frequency divider 1, 5... Counter, 6... Subtractor, 7... E
S (elastic store), 8... selector, 9...
・Adder, 10... Integrator, 11... Digital
Analog converter, 12...VCO (voltage controlled crystal oscillator). 13...Reproduction sampling frequency output terminal.

Claims (1)

[Claims] 1) Reproducing an image signal transmitted via a digital communication circuit operating at a transmission frequency f_L at a sampling frequency f
In a device that reproduces at _S_R, the transmission line frequency f_
a first frequency divider that divides L into 1/M; a second frequency divider that divides the reproduced sampling frequency f_S_R into 1/N;
a reproduction-side counter that counts the frequency divided by the second frequency divider with the period of the frequency divided by the first frequency divider; and a transmission-side counter that divides the transmission line frequency f_L into 1/M on the transmission side. The transmission sampling frequency f_S_S is 1/
A subtractor that calculates the difference between the frequency information on the transmitting side that is obtained by counting the frequency divided by N by the transmitting side counter and the frequency information counted on the reproducing side counter, and temporarily stores the transmitted data. means for correcting the output of the subtracter according to the phase difference between writing and reading of the storage data; an integrator for integrating the value output from the correction means; and an integrator for integrating the value output from the integrator. A digital-to-analog converter performs digital-to-analog conversion, and a reproduction sampling frequency f_S is determined by the value output from the digital-to-analog converter.
A sampling frequency control method characterized by comprising a voltage controlled crystal oscillator that oscillates a frequency of _R. 2) In the sampling frequency control method according to claim 1),
The correction means selects and outputs one of a plurality of predetermined values according to the phase difference between the elastic store that temporarily stores the transmitted data and the write/read pointer of the elastic store. and an adder that adds the frequency information difference output from the subtracter and the value output from the selector. 3) In the sampling frequency control method according to claim 2),
The sampling frequency control method is characterized in that the selector has three values, +α, 0, and −α, as the plurality of predetermined values.