JP2000031947A - Sampling frequency converter and electronic equipment provided with the converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert a sampling frequency without measuring and recognizing a 2nd sampling frequency in advance in the case of converting a 1st sampling frequency into a 2nd sampling frequency of other device and transmitting information. SOLUTION: A sample interpolation means 35 interpolates information sampled by a 1st sampling frequency F1 and a first-in first-out storage means 37 stores the interpolated sample. The interpolated sample is read by a variable sampling frequency from a variable sampling frequency generating means 40 that is discrete-feedback-controlled so that the variable sampling frequency is equal to a 2nd sampling frequency F2 in the case of conversion of control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a sampling frequency converter, and more particularly, to a sampling frequency converter by automatic control for converting a sampling frequency.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a schematic configuration of a conventional sampling frequency converter. Information is sampled by means 1
In, the sampled signal by sampling frequency F _1. The signal is inputted to the first device 19, synchronized with the sampling frequency F _1, and n times of F ₁ (n is an integer) oversampling filter 4 by the sampling frequency n × F ₁ of
Is sampled again. After the return signal is removed as necessary, the signal is input to the second device 20. Input signal is sampled information at a sampling frequency F ₂ at the sampling means 9. Further, depending on the frequency ratio between the sampling frequency F ₁ and the sampling frequency F ₂ , a sample value interpolating means for interpolating the sample value may be provided at a stage preceding the sampling means 9 (not shown).

On the other hand, the sampling frequency F ₁ and the sampling frequency F
Between ₂ relationship of _{n × F 1 = m × F} 2 (n, m are integers). The sampling frequency nF ₁ is calculated by the counting means 8 as (m /
n) multiplied by equals the sampling frequency F _2. Counting means 8
Is compared in phase with the sampling frequency F ₂ of the second device 20 by the comparing means 7. The output frequency of the frequency varying means 6 is controlled by the output of the comparing means 7. As a result,
Sampling frequencies F ₁ phase of the sampling frequency F ₂ inherent to the second device 20 inherent in the first device is synchronized.

It has been described above that information sampled at the sampling frequency F ₁ is converted to the sampling frequency F ₂ . A feedback control loop constituted by the frequency variable means 6, the counting means 8, and the comparing means 7 is a so-called PLL (Phase Synchronous Control Loop, hereinafter referred to as PLL).
It is called.

The first device 19 described above is, for example, a personal computer or a set-top box, and the second device 20 is, for example, an audio module or a video used in phase synchronization with the first device 19. Electronic devices such as modules, and electronic devices such as audio devices and video devices. 2. Description of the Related Art In recent years, as personal computers, set-top boxes, audio equipment, video equipment, mobile phones, and the like are used in a network, a sampling frequency conversion apparatus that can easily convert a sampling frequency while performing phase synchronization is required. Have been.

[0006]

The conventional sampling frequency converter has the following problems. That is, PL
L23 in the counting means 8, since it is necessary to determine the aforementioned (m / n), it is necessary to know to measure the advance of the sampling frequencies F ₁ and the sampling frequency F ₂ relationship.
In other words, without knowing both sampling frequency F ₂ and the sampling frequencies F ₁ and first device 19, a problem that it is impossible to convert the sampling frequency takes a phase synchronization between the second device 20 was there.

In the conventional sampling frequency conversion device, the PLL 23 is almost always constituted by hardware, so that only a certain PLL is provided between a specific device and another specific device. There was no limit to the restrictions, such as the provision of In addition, there is a problem that a device having a built-in PLL constituted by such hardware has a large configuration scale corresponding to the PLL.

[0008] The present invention has been made in view of these points, it is not necessary to know in advance measures the ratio of the sampling frequencies F ₁ and sampling frequency F _2, also can be configured in software, optionally It is an object of the present invention to provide a sampling frequency conversion device capable of performing sampling frequency conversion in phase synchronization between the above devices and an electronic apparatus including the same.

[0009]

In order to solve the above-mentioned problems, in a sampling frequency conversion device of the present invention and an electronic device equipped with the same, information sampled at a first sampling frequency is A sampling frequency conversion device that converts information sampled at an unknown sampling frequency into an interpolated sample value from information sampled at a first sampling frequency, and calculates an interpolated sample value at a variable sampling frequency. Sample value interpolation means for sampling;
A first-in first-out storage means for storing interpolation sample values at a variable sampling frequency; an interpolation sample value stored in the first-in first-out storage means is read at an unknown sampling frequency; and storage of the read interpolation sample values is first-in first-out. Reading means for deleting from the storage means, storage occupancy observation means for observing the number of interpolated sample values in the first-in first-out storage means,
A variable sampling frequency generating unit configured to generate a variable sampling frequency under the control of the storage occupancy monitoring unit; and a variable sampling frequency initial phase setting unit configured to set an initial phase of the variable sampling frequency. Features.

Preferred embodiments of the sampling frequency conversion device of the present invention and electronic equipment having the same are as follows.

The sample value interpolating means, the reading means, the storage occupation amount observing means, the variable sampling frequency generating means, and the variable sampling frequency initial phase setting means can be constituted by software.

At the start of the sampling frequency conversion, the reading means reads out from the FIFO memory until the ratio of the number of interpolated sample values to the storage capacity of the FIFO memory reaches 50%. This prevents the interpolated sample values from being read.

Discrete feedback control comprising sample value interpolation means, first-in first-out storage means, reading means, storage occupancy observation means, variable sampling frequency generation means, and variable sampling frequency initial phase setting means. Time τ required for control convergence of the loop, F ₂ ′ (j) representing a variable sampling frequency in an arbitrary j-th discrete feedback control generated by the variable sampling frequency generating means, and unknown sampling frequency F _2, between the storage capacity of BF-first-out memory means ^{_{| ∫ t 0 {F 2 -F}} 2 '(j)} dt
0.5 ≦ BF, where 0 <t ≦ τ, so that the storage capacity BF of the first-in first-out storage means can be secured.

The operation of the above means will be described below. The above-mentioned first-in first-out storage means and storage occupancy observation means perform the variable sampling when the speed at which the sample value from the sample value interpolation means is stored in the first-in-first-out storage means is equal to the reading speed from the first-in first-out storage means by the reading means. The variable sampling frequency F ₂ ′ (j) generated by the sampling frequency generation means is equal to the unknown sampling frequency F ₂ which is the reading speed of the reading means.

The sample value interpolating means, the memory occupancy observing means, the variable sampling frequency generating means, and the variable sampling frequency initial phase setting means are implemented by software using a part of a control program of an electronic device using a microcomputer. Can be configured.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention comprises a sampling frequency conversion device for converting information sampled at a first sampling frequency into information sampled at a second sampling frequency, and a sampling frequency conversion device. It can be applied to electronic devices. The second sampling frequency may be unknown. FIG. 1 is a block diagram showing a schematic configuration of a sampling frequency conversion device 41 of the present invention. The information is sampled by the sampling means 30 at the sampling frequency F ₁ , and
Sampling frequency n × F ₁ is an integer multiple of the sampling frequencies F ₁ by (n is an integer) are sampled at. Also, the aliasing signal is removed as needed.

As described above, when the Nyquist condition is not satisfied between the sampling frequency F ₁ and the unknown sampling frequency F ₂ , the cut-off frequency of the oversampling filter 34 is sampled at the sampling frequency F ₁ . to prevent aliasing signals caused by direct sampling at the unknown sampling frequency F ₂ of the information that is, it must be set.

The output of the oversampling filter 34 is input to a sample value interpolating means 35 described later. The output of the sample value interpolation means 35 is stored in the first-in first-out storage means 37. The first-in first-out storage means 37 is a so-called FIFO
This is a storage means in which the interpolation sample value stored first is read out first. Stored interpolated sample value by reading means 38, a second sampling frequency first-in-first-out memory means 3 (unknown sampling frequency) F ₂
7 is read. The reading means 38 reads the interpolated sample values and deletes the storage of the interpolated sample values.

The storage occupancy observing means 39 observes the number of interpolated sample values in the first-in first-out storage means 37 after a lapse of a predetermined period T, and if the number increases, the storage from the sample value interpolating means 35 to the first-in first-out storage means 37. If it is determined that the speed is faster than the reading speed from the first-in first-out storage unit 37 and the speed is reduced, the storage speed from the sample value interpolation unit 35 to the first-in-first-out storage unit 37 is lower than the reading speed from the first-in-first-out storage unit 37. Judge.

The storage occupancy monitoring means 39 controls the variable sampling frequency generation means 40 based on the relationship between the storage speed from the sample value interpolation means 35 to the first-in first-out storage means 37 and the reading speed from the first-in first-out storage means 37. And
The variable sampling frequency F ₂ ′ (j) of the sample value interpolation means 35 is controlled. As a result, the speed of storing the interpolated sample values from the sample value interpolating means 35 to the first-in first-out storage means 37 is equal to the reading speed of the reading means 38. That is, the variable sampling frequency F ₂ ′ (j) generated by the variable sampling frequency generation unit 40 is equal to the second sampling frequency (unknown sampling frequency) F ₂ that determines the reading speed.

Here, j is an integer, and the above-mentioned sample value interpolation means, first-in first-out storage means, read means, storage occupancy observation means, variable sampling frequency generation means, variable sampling frequency initial phase An index indicating the j-th of the discrete feedback control loop constituted by the setting means and the variable sampling frequency F ₂ ′ (j) is the j-th index.
Variable sampling frequency for the second discrete feedback.

Next, the operation of the sample value interpolation means 35 will be described. FIG. 2 illustrates the operation of sampling the output sample value from the oversampling filter 34 using the sampling frequency from the variable sampling frequency generation unit 40 and interpolating using the sample value interpolation unit 35.

In FIG. 2, the period T ₀ is the period of the sampling frequency of the oversampling filter 34, and T ₀
= 1 / (sampling frequency n × F ₁ ). Also, the period T
₂ ′ (j) is the period of the variable sampling frequency F ₂ ′ (j) from the variable sampling frequency generation means 40. Arbitrary positions k × T ₀ (point B) and (k
+1) × T ₀ (point C), i-th sample point position i × T
Suppose that ₂ '(j) (point A) enters. However, i and k are arbitrary integers and have a relationship described later. In this case, when the phase of the point C in the oversampling sampling period T ₀ and the point B is determined as a reference, the following equation (1) is obtained.

2π × {(i × T ₂ ′ (j) −k × T ₀ ) / T ₀ } (1) where i × T ₂ ′ (j)> k × T ₀ The period of the sampling frequency F ₁ is T ₁
Then, since T ₁ = n × T ₀ , the following equation (2) is obtained by rewriting equation (1) using this. Φ = 2π × {i × n × (T ₂ ′ (j) / T ₁ ) −k} (2) where (T ₂ ′ (j) / T ₁ ) = m (j)
The following equation (3) holds. Φ = 2π × {i × n × m (j) −k} (3) Next, i and k have the following relationship. For example, m
(J) = T ₂ ′ (j) / T ₁ = 1.2 and n = 3, i = 1, 2, 3,... I × n × m
(J) = 3.6, 7.2, 10.8. At this time,
k = 3, 7, 10,... That is, k is i × n × m
The value of (j) is truncated below the decimal point. If this truncation after the decimal point is written as [i × n × m (j)], then k = [i × n × m (j)]. Therefore, equation (3) is rewritten to obtain the following equation (4). Φ = 2π × {i × n × m (j) − [i × n × m (j)]} (4)

From the above equation (4), the sampling frequency F
Position of the sample point A when normalized by _one cycle T ₁ is i
× n × m (j), and the position of sample point B is k = [i × n
× m (j)]. FIG. 3 is a partial view of sample points A, B, and C in FIG. In FIG. 3, an interpolated sample value Y is obtained by interpolating a sample point G by a sample point D and a sample point F as in the following equation (5).
(I, j) is obtained. Y (i, j) = {X (k + 1) −X (k)} (i × n × m (j) −k) + X (k) = ｛X ([i × n × m (j)] + 1) −X [i × n × m (j)]｝ × (Φ / 2π) + X ([i × n × m (j)] (5)

As described above, the variable sampling frequency generating means 40 reads out the period T ₂ ′ (j) of the variable sampling frequency F ₂ ′ (j) based on the control signal from the storage occupancy monitoring means 39. , Ie, the period T ₂ of the _second sampling frequency (unknown sampling frequency) F ₂ , and finally becomes equal to the unknown sampling frequency F ₂ . That is, from the viewpoint of the conversion of the sampling frequency, without knowing in advance measures the ratio of the sampling frequencies F ₁ and sampling frequency F _2, information sampled by the sampling frequencies F ₁ is the second It will have been converted into the sampling frequency the sampled information (unknown sampling frequency) F _2.

Variable sampling frequency initial phase setting means 36
Is a variable sampling frequency F ₂ ′ (j) (period T) generated by the variable sampling frequency generation unit 40 as shown in FIG.
₂ '(j)) is set.

FIG. 4 is a flowchart showing the detailed operation of the sampling frequency converter 41 of the present invention described above. A supplementary description of the main parts will be given below, and a desirable mode of the sampling frequency conversion device 41 of the present invention will also be described. [S-6] First-in first-out storage unit 37 until the storage occupancy of first-in-first-out storage unit 37 becomes 50%.
Is in a standby state without reading the interpolated sample value from. This is the time until the speed at which the interpolated sample values are stored in the first-in first-out storage means 37 and the speed at which the interpolated sample values are read out reach equilibrium, that is, the sample value interpolation means 35, the first-in first-out storage means 37, Until the control of the discrete feedback control loop composed of the occupation amount observation means 39, the variable sampling frequency generation means 40, and the variable sampling frequency initial phase setting means 36 is converged,
The reading means 38 from the first-in first-out storage means 37 secures the number of interpolated sample values to be read at an unknown sampling frequency F _{2 so} that the storage occupancy monitoring means 39 can observe the number of interpolated sample values in the first-in first-out storage means 37. This is for initial setting. That is, the first-in first-out storage means 3
The storage occupancy of No. 7 increases and decreases at 50%. This is one of the desirable forms of the sampling frequency conversion device of the present invention and the electronic equipment provided with the same.

Further, the sampling frequency conversion device 41 of the present invention
One of the desirable forms of is that the unknown sampling frequency F ₂ ,
The storage frequency of the interpolated sample values in the first-in first-out storage means 37, that is, the sampling frequency F ₂ ′ (j) from the variable sampling frequency generation means 40, the sample value interpolation means 35, the first-in first-out storage means 37, and the storage occupation Quantity observation means 39
And the time τ required for control convergence of the discrete feedback control loop including the variable sampling frequency generation means 40 and the variable sampling frequency initial phase setting means 36, and the storage capacity BF of the first-in first-out storage means 37. It is desirable that the following equation (6) is satisfied. ^{_{| ∫ t 0 {F 2 -F}} 2 '(j)} dt | ≦ 0.5 × BF (6) where 0 <t ≦ τ Here, the left side of the equation (6) | | denotes the absolute value, ｜ ∫
^t ₀ ｛F ₂ −F ₂ ′ (j)｝ dt | indicates the increase or decrease of the interpolated sample value of the first-in first-out storage means 37 at an arbitrary time t of the above-described feedback control.

The right side BF of the equation (6) indicates the storage capacity to be secured by the first-in first-out storage means 37, and as described above,
In the initial state, it is multiplied by 0.5 considering that the storage occupancy of the first-in first-out storage means 37 is set to 50%. That is, from the above, the maximum amount of increase or decrease of the interpolated sample value of the first-in first-out storage means 37 must be less than half of the storage capacity of the first-in-first-out storage means 37 until the above-described discrete feedback control converges. No.
In the sampling frequency conversion device of the present invention, the storage capacity BF is secured for any unknown sampling frequency.

"S-13 to S-18" Buf (j) is the number of interpolated sample values in the first-in first-out storage means 37.
Here, j is an interpolated sample value on a first-in first-out storage means 37.
, Ie, the same index as in the case of the sampling frequency F ₂ ′ (j) from the variable sampling frequency generation means 40.

That is, the storage capacity occupation ratio Buf of the current first-in first-out storage means 37 at every predetermined period T described above.
The difference DBuf between (j) and the storage capacity occupancy Buf (j-1) of the previous first-in first-out storage means 37 is measured, and DBuf is measured.
In the case of = 0, the observation is continued without doing anything. In the case of DBuf> 0, a command to lower the variable sampling frequency F ₂ ′ (j) of the variable sampling frequency generation means 40 is issued, and in the case of DBuf <0, Generate a rising command.

[S-2] At the beginning of the feedback control, the initial sampling frequency m (0) is determined by the variable sampling frequency generation means 40, and the initial phase is determined by the variable sampling frequency initial phase setting means 36. . Where m (0) =
(Sampling frequency F ₁ / Variable sampling frequency F ₂ ′ (j))
It is.

[S-3 to S-5] The sample from the oversampling filter 34 is sampled at the sampling point position of the sampling frequency F ₂ ′ (j) from the variable sampling frequency generating means 40. And the result is stored in the first-in first-out storage means 37.

The sampling frequency converter 41 of the present invention has been described in detail above. One of the desirable embodiments of the sampling frequency conversion device of the present invention and the electronic apparatus including the same is as described above, wherein the sample value interpolation means, the reading means, the storage occupancy observation means, the variable sampling frequency generation The means and the variable sampling frequency initial phase setting means can be configured by software. With this configuration, a part of the software of the microcomputer used in the existing electronic device can be used, and the configuration size of the electronic device can be reduced.

The sampling frequency conversion device 41 is provided in a personal computer, a set-top box, or the like, and is connected to other devices, for example, electronic devices such as an audio module, a video module, an audio device, a video device, and a mobile phone. when, as a sampling frequency of these other devices (read frequency of the aforementioned reading means 38, that corresponds to a second sampling frequency F ₂₎ was even unknown, performs sampling frequency conversion be able to.

[0037]

According to the present invention, when two devices having different sampling frequencies are used and the sampling frequency is converted and information is transmitted from one device to the other device, the sampling frequency of the other device is measured in advance. Without knowing it, it became possible to transmit information by converting the sampling frequency to the sampling frequency of the other device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a sampling frequency conversion device according to the present invention.

FIG. 2 is a schematic diagram illustrating a relationship between a sampling frequency of an oversampling filter and a sampling frequency of a sample value interpolation unit.

FIG. 3 is a schematic diagram showing an operation of a sample value interpolating unit by enlarging a portion of FIG. 2 and performing normalization;

FIG. 4 is a flowchart showing a detailed operation procedure of the sampling frequency conversion device of the present invention.

FIG. 5 is a block diagram showing a schematic configuration of an example of a conventional sampling frequency conversion device.

[Explanation of symbols]

1, 9, 30, ... sampling means, 5, 8 ... counting means, 6 ...
Frequency changing means, 7 Comparison means, 4, 34 oversampling filter, 23 PLL (phase locked loop), 19 first device, 20 second device, 35 sample value interpolation means, 36 Variable sampling frequency initial phase setting means, 37: first-in first-out storage means, 38: reading means, 39: storage occupancy observation means, 40: variable sampling frequency generation means, 41: sampling frequency conversion device

Claims (5)

[Claims] 1. A sampling frequency conversion device for converting information sampled at a first sampling frequency into information sampled at an unknown sampling frequency, comprising: Sample value interpolation means for calculating an interpolation sample value from the sampled information and sampling at a variable sampling frequency; a first-in first-out storage means for storing the interpolation sample value at the variable sampling frequency; The interpolation sample value stored in the first-in first-out storage means is
Reading means for reading out at the unknown sampling frequency and deleting the storage of the read-out interpolation sample value from the first-in first-out storage means; and storage occupancy for observing the number of the interpolation sample values in the first-in first-out storage means. Quantity observing means, variable sampling frequency generating means for generating the variable sampling frequency under the control of the storage occupancy observing means, and a variable sampling frequency initial phase for setting an initial phase of the variable sampling frequency. A sampling frequency conversion device, comprising: a setting unit. 2. The apparatus according to claim 2, wherein said sample value interpolation means, said read means, said storage occupancy observation means, said variable sampling frequency generation means, and said variable sampling frequency initial phase setting means are constituted by software. Claim 1 characterized by the following:
2. The sampling frequency conversion device according to 1. 3. Immediately after the sampling frequency conversion is started, the first-in first-out memory is read by the first-in first-out storage unit until the ratio of the number of interpolated sample values in the first-in first-out storage unit to the storage capacity of the first-in first-out storage unit reaches 50%. 2. The sampling frequency conversion device according to claim 1, wherein the interpolation sample value is not read from the storage unit. 4. The sample value interpolation means, the first-in first-out storage means, the reading means, the storage occupancy observation means, the variable sampling frequency generation means, and the variable sampling frequency initial phase setting means. The time required for control convergence of the discrete feedback control loop composed of
F ₂ ′ (j) representing the variable sampling frequency in an arbitrary j-th discrete feedback control generated by the variable sampling frequency generation means, the unknown sampling frequency F _2, and the first-in first-out storage means Storage capacity BF
^{_{There, | ∫ t 0 {F 2}} -F 2 '(j)} dt | ≦ 0.5 × B
2. The sampling frequency conversion apparatus according to claim 1, wherein the storage capacity BF of the first-in first-out storage unit can be secured so that F, (where 0 <t ≦ τ). 5. An electronic apparatus comprising the sampling frequency conversion device according to claim 1.