JPH0250507A - Sampling frequency converter - Google Patents

Abstract

PURPOSE:To convert a digital signal to the signal of a different sampling frequency has it is by thinning the frequency spectrum component of a sampling input signal by a special digital filter, interpolating the spectrum component of the thinned frequency area with a thinning circuit and alternatively repeating the thinning and interpolation. CONSTITUTION:A thinning circuit 3 to interpolate, in accordance with the multiple of 1/3, a frequency area thinned by an oversampling digital filter 2 to execute the thinning of a frequency area in according with the multiple to '4', a five-fold oversampling digital filter 4, a 1/7 thinning circuit 6, an light-fold oversampling digital filter 7 and a 1/7 thinning circuit 8 are connected to a cascade between input output terminals. A sampling input signal successively receives the thinning of the frequency area and the interpolation between thinned frequency areas. Thus, the sampling input signal is not converted to an analog signal and can be directly converted to digitally to a different sampling frequency signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sampling frequency converter suitable for digital audio equipment, digital communication systems, etc.

[Summary of the invention] A sampling frequency converter that converts a sampling input signal with a sampling interval of 1/f, see into a sampling output signal with a different sampling interval of 1/(M/N)f (M and N are integers). A pair or a plurality of pairs of oversampling filters and decimation circuits having low-pass characteristics are provided in series, and the frequency domain decimation according to a predetermined multiple by the digital filter and the decimated frequency by the time domain decimation circuit are performed. Interpolation according to a predetermined area ratio is alternately repeated once or multiple times.

[Prior Art] In digital audio devices, for example, a digital playback signal from a CD player is transferred between devices with different sampling frequencies to a digital audio tape recorder (
In order to perform recording and playback using DAT), the sampling frequency between the two is different, so it is not possible to directly transmit and receive signals in digital form.

Therefore, in the past, the digital reproduction signal was once converted into an analog signal and then sampled at the DAT sampling frequency.

[Problems to be Solved by the Invention] However, it is clear that if the analog signal is converted into an analog signal and then sampled again, the S/N will deteriorate.

Therefore, a method has been proposed in which the sampling frequency of the sampling input signal is appropriately interpolated digitally to convert it into a sampling output signal with a different sampling frequency, but from a signal theory perspective, distortion always occurs, S/N
deterioration is inevitable.

[Object of the Invention] Therefore, the object of the present invention is to provide a sampling method that can directly convert a sampling input signal into a signal of a different sampling frequency as a digital signal without converting it into an analog signal, and that eliminates distortion and S/N deterioration. To provide frequency converter.

[Means for Solving Problem i] In order to achieve the above object, the sampling frequency converter of the present invention includes one or more oversampling digital filters having low-pass characteristics, and a thinning filter paired with the digital filters. The circuit is connected in cascade between the input and output terminals, and the frequency domain spectral components of the sampling input signal applied to the input terminal are thinned out by the first pair of digital filters according to a predetermined multiple, and the thinned out frequency domain spectral components are is interpolated by the pair of time domain decimation circuits according to a predetermined ratio, and thereafter this decimation and interpolation are sequentially repeated alternately to obtain a sampling output signal from the output terminal at a sampling interval different from the sampling interval of the input signal. It is characterized by having been configured.

[The effect cosampling input signal is successively decimated in its frequency domain and interpolated between the decimated frequency domains by each pair of series-connected oversampling digital filters and a decimation circuit to obtain a desired sampling frequency. converted into a sampled output signal.

[Example] The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 1 shows an example of a sampling frequency converter according to the present invention, with a sampling frequency f1=44.0kHz.
The sampling input signal Si is set to a sampling frequency f2
= 48.0kHz sampling output signal S. In the figure, 1 is an input terminal, 2 is an oversampling terminal that performs 4 times oversampling (thinning of the frequency domain according to a multiple of 4). Digital filter 3 converts the frequency domain thinned out by filter 2 into 1
A decimation circuit that interpolates according to multiples of 73, 4 is a 5x oversampling digital filter, 6 is 1/7
A decimation circuit, 7 is an 8x oversampling digital filter, 8 is a 1/7 decimation circuit, and 9 is an output terminal, and these oversampling digital filters and decimation circuits are connected in cascade between the input and output terminals. ing.

The decimation multiple of 4.5°8 and the interpolation multiple of 1/3.1/7.1/7 in the frequency domain are determined as follows.

That is, in the relationship between fi and f2, the numerator of the above fraction represents the oversampling multiple, and the denominator represents the interpolation ratio. The numerator value is decomposed into multiples of the oversampling that can be realized in the actual circuit, and the denominator value is decomposed into ratios such that their spectra do not overlap even if the frequency domain is interpolated, and the signal processing is performed in several steps. Make sure to do the following.

For example, suppose . Therefore, circuits 2, 3: 4, 5: 6, and 7 constitute a pair of sampling frequency conversion means, respectively.

FIG. 2 is a diagram showing oversampling and interpolation by each pair of circuits in the above embodiment.

The oversampling digital filter and the decimation circuit are known per se, and the attenuation rate of the filter is set so that when the frequency domain is decimated, the noise is at a level below the quantization noise. The thinning circuits operate in synchronization with a common clock signal.

[Effects of the Invention] As explained above, according to the present invention, a sampling input signal can be directly converted into a signal with a different sampling frequency digitally without converting it into an analog signal, and moreover, it is possible to directly convert a sampling input signal into a signal with a different sampling frequency without deterioration of S/N. and does not cause distortion.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a frequency spectrum diagram for explaining its operation. 1... Input terminal, 2, 4.6...
...oversampling digital filter,
3,5.7... Thinning circuit, 8...
...Output terminal. Patent applicant Kyocera Corporation

Claims (1)

[Claims] One or more oversampling digital filters with low-pass characteristics and a decimation circuit paired with the digital filters are connected in cascade between input and output terminals, and the frequency domain of the sampling input signal applied to the input terminals is The periodically existing spectral components are thinned out according to a predetermined multiple by the first pair of digital filters, and the thinned out frequency domain spectral components are interpolated by the time domain thinning circuit of the pair according to a predetermined ratio. A sampling frequency converter characterized in that it is configured to alternately repeat thinning and interpolation to obtain a sampling output signal from an output terminal at a sampling interval different from the sampling interval of the input signal.