JP2002185323A - Sampling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the circuit scale of a sampling device that samples video signals of a plurality of kinds of formats without generating any reflecting noise. SOLUTION: A prefilter 2 limits the band of input analog video signals. A clock generating circuit 10 generates a first clock having the first frequency corresponding to the format of the analog video signals. Another clock generating circuit 6 generates a second clock having a fixed second frequency. An A/D converter 5 performs A/D conversion on the output of the prefilter 2 based on the second clock. A sampling rate converting circuit 9 converts a sampling rate in such a way that the circuit 9 converts the output of the A/D converter 5 into the data rate of the first frequency by using the coefficient generated from a coefficient generating circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sampling device capable of sampling video signals of a plurality of formats.

[0002]

2. Description of the Related Art When an analog video signal is sampled by a sampling device, a pre-filter is provided before an A / D converter in order to remove aliasing noise, and the band of an input video signal is reduced by 1/1 of a sampling clock.
It needs to be limited to 2. When sampling video signals of a plurality of types of formats, a sampling clock is required in accordance with the video signal of each format, and a prefilter is also required for each type of sampling clock.

FIG. 2 is a block diagram showing an example of a conventional sampling device. Here, a case is shown in which video signals of two types of formats are sampled. In FIG. 2, an analog video signal input to an input terminal 1 is input to prefilters 2 and 3. As described above, the pre-filters 2 and 3 limit the band so as not to generate aliasing noise. Outputs of the prefilters 2 and 3 are input to terminals a and b of the selection circuit 4, respectively.

A selection circuit 4 selects a terminal a, which is an output of the prefilter 2, and a terminal b, which is an output of the prefilter 3, according to a selection signal input from an input terminal 8, and A / D
Input to the converter 5. The selection signal input from the input terminal 8 is in accordance with the format of the input video signal.

On the other hand, the clock generation circuit 6 has an input terminal 8
A sampling clock corresponding to the format of the input video signal is generated based on the input selection signal, and input to the A / D converter 5. The A / D converter 5 performs A / D conversion on the video signal supplied from the selection circuit 4 based on the clock supplied from the clock generation circuit 6.
The video signal converted into a digital signal by the A / D converter 5 is output from an output terminal 7.

By the way, the scanning line 5 such as the NTSC signal is used.
When sampling 25 interlaced signals (525i) (480 effective scanning lines), 14.3 MHz
The sampling clock is generally used. The pre-filter for removing aliasing noise is a low-pass filter having a cutoff frequency of about 7 MHz. The scanning line 52
5 (480 effective scanning lines) progressive signals (5
When sampling 25p), sampling is generally performed with a sampling clock of 28.6 MHz. The pre-filter for aliasing noise removal has a cutoff frequency of about 14
MHz low-pass filter.

In the conventional sampling apparatus shown in FIG. 2, in order to handle signals of both 525i and 525p, the cutoff frequencies of the prefilters 2 and 3 are set to about 7 MHz, respectively.
z, about 14 MHz. Further, the clock generation circuit 6 needs to generate two types of clocks, 14.3 MHz and 28.6 MHz. The selection circuit 4 selects the terminal a if the input video signal is 525i, and selects the terminal b if the input video signal is 525p.

[0008]

As described above, in the conventional sampling device, two types of pre-filters 2 and 3 and a selection circuit 4 are required to sample video signals of two types of formats. . Therefore, the circuit scale increases and the cost also increases. As the number of types of formats handled increases, the number of pre-filters must be increased, so that the circuit scale is further increased and the cost is further increased.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a circuit scale of a sampling device capable of sampling video signals of a plurality of formats without generating aliasing noise. And to provide a sampling device that can be realized at low cost.

[0010]

According to the present invention, there is provided a sampling apparatus for converting an input analog video signal into a digital video signal in order to eliminate aliasing noise. A prefilter (2) for limiting a band of a video signal, a first clock generation circuit (10) for generating a first clock having a first frequency according to a format of the analog video signal, Fixed second higher than the frequency of
A second clock generation circuit (6) for generating a second clock having a frequency of (A) and an analog video signal output from the pre-filter based on the second clock.
A / D that outputs a first digital video signal having a data rate of the second frequency by performing A / D conversion
A converter for generating a coefficient corresponding to the format of the analog video signal; a filter for converting a sampling rate; the first clock; the second clock; And a sampling rate for inputting the clock and the coefficient, converting the first digital video signal to a second digital video signal having a data rate of the first frequency using the coefficient, and outputting the converted digital video signal. A sampling device characterized by comprising a conversion circuit (9).

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sampling device according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing one embodiment of the sampling device of the present invention. In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, an analog video signal input to an input terminal 1 is input to a pre-filter 2 comprising a low-pass filter. The pre-filter 2 limits the band so as not to generate aliasing noise. Assuming that the frequency of the clock generated by the clock generation circuit 10 described later is fs and the frequency of the sampling clock generated by the clock generation circuit 6 is M times fs (M> 1),
The cutoff frequency of the pre-filter 2 corresponds to the clock of the frequency Mfs. Note that M is a variable, and the frequency Mfs is constant.

The output of the prefilter 2 is input to an A / D converter 5. The A / D converter 5 includes a clock generation circuit 6
A clock having a frequency Mfs, which is a fixed frequency, is input, and the A / D converter 5 A / D converts the input video signal based on the clock having the frequency Mfs. The video signal converted into a digital signal by the A / D converter 5 is input to a sampling rate conversion circuit 9.

The clock generation circuit 10 generates a clock having a frequency fs according to the format of the input video signal (the number of pixels in the horizontal period) according to the control signal input from the input terminal 8. The clock generation circuit 6 varies the magnification M according to a control signal input from the input terminal 8 and generates a clock having a constant frequency Mfs. A clock having a frequency Mfs from the clock generation circuit 6 and a clock having a frequency fs from the clock generation circuit 10 are input to the sampling rate conversion circuit 9.

The coefficient generation circuit 11 generates a coefficient used in a filter constituting the sampling rate conversion circuit 9 according to a control signal input from the input terminal 8.
As the sampling rate conversion circuit 9 itself, a known one configured by an FIR filter (polyphase filter) can be used. The coefficients of the filter generated by the coefficient generation circuit 11 correspond to the format of the input video signal.

The sampling rate conversion circuit 9 converts the digital video signal of the sampling rate Mfs input from the A / D converter 5 into a digital video signal of the sampling rate fs using the coefficient input from the coefficient generation circuit 11. I do. The video signal whose sampling rate has been converted by the sampling rate conversion circuit 9 is output from the output terminal 7.

With the above-described configuration, the A / D converter 5 performs the format of the input video signal (the number of pixels in the horizontal period).
A / D conversion is performed with a clock of frequency Mfs, which is a constant clock regardless of. Therefore, the pre-filter 2
One type of low-pass filter corresponding to the frequency Mfs may be used. In this manner, the sampling apparatus of the present invention can sample video signals of a plurality of formats without generating aliasing noise. The sampling device of the present invention has a small circuit scale and can be realized at low cost.

[0018]

As described above in detail, the sampling apparatus according to the present invention comprises a pre-filter for limiting a band of an analog video signal for removing aliasing noise, and a first frequency corresponding to a format of the analog video signal. A first clock generating circuit for generating a first clock having a first frequency, a second clock generating circuit for generating a second clock having a fixed second frequency higher than the first frequency, and a pre-filter. An A / D converter that outputs a first digital video signal having a data rate of a second frequency by A / D converting the output analog video signal based on a second clock; and an analog video signal. And a filter for converting a sampling rate. A first clock, a second clock, And the clock, the coefficient is input,
A sampling rate conversion circuit configured to convert a first digital video signal into a second digital video signal having a data rate of a first frequency by using a coefficient and convert the sampling rate into a second digital video signal. The circuit scale of a sampling device that can sample a video signal in a format without generating aliasing noise can be reduced, and it can be realized at low cost.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 2 Pre-filter (low-pass filter) 5 A / D converter 6, 10 Clock generation circuit 9 Sampling rate conversion circuit 11 Coefficient generation circuit

Claims (1)

[Claims] 1. A sampling device for converting an input analog video signal into a digital video signal, comprising: a pre-filter for limiting a band of the analog video signal in order to remove aliasing noise; A first clock generation circuit for generating a first clock having a first frequency, and a second clock generation circuit for generating a second clock having a fixed second frequency higher than the first frequency A / D converting the analog video signal output from the pre-filter based on the second clock to output a first digital video signal having a data rate of the second frequency. A D converter, a coefficient generation circuit for generating a coefficient according to a format of the analog video signal, and a sampling rate. It has a filter for converting,
The first clock, the second clock, and the coefficient are input, and the first digital video signal is converted into a second digital video signal having a data rate of the first frequency by using the coefficient. And a sampling rate conversion circuit for converting and outputting a sampling rate.