JP2001230837A - Telephone terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a telephone terminal that eliminates a noise caused by a slip of voice data due to a difference of a clock between a PC and the telephone terminal in the case of connecting the PC and a phone exchange network with a USB interface in an asynchronous transfer mode. SOLUTION: An SOF counter 21 and a TEL frame counter 22 respectively count frame synchronizing signals of an SOF and a 2nd (TEL sid) CODEC 4, a comparator arithmetic unit 23 conducts comparison arithmetic operations, and a frequency selector 28 receiving the result of the comparison arithmetic operation selects a drive speed (clock) of a 1st (PC side) CODEC 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone terminal device, particularly a telephone terminal device for transmitting and receiving voice, using a PC (Personal Computer) and a USB (Universal Serial Bus) interface in an isochronous transfer mode (hereinafter referred to as "asynchronous transfer mode"). ") When performing voice data communication, the telephone terminal device preventing occurrence of noise due to slip of voice data due to a clock difference between the PC and the telephone device.

[0002]

2. Description of the Related Art In the prior art, a PC and a telephone exchange network are
When connecting in the asynchronous transfer mode of the B interface,
CODEC 2 for voice data transfer with telephone switching network
Using the analog signal to combine voice. Since an error occurs in the SOF (Start of Frame: a frame signal transmitted from the PC at a period of about 1 ms in the asynchronous transfer mode) output from the PC, C generated based on the error is generated.
The ODEC frame synchronization signal includes an error. In order to absorb this error, the digital audio data sent to the PC-side CODEC has been buffered using four stages of FIFO. Then, a clock generation switching circuit capable of monitoring the amount of data in the FIFO and switching the clock frequency of the PC side CODEC and the frame signal cycle according to the situation is provided.

[0003]

In a system in which the clock of the PC for digitizing the voice signal and the transmission clock of the telephone switching network run independently, if the two clocks are not synchronized, loss of the digital voice signal, Overflow occurs and becomes audible noise when converted to analog. In the related art, a PC side CODEC (a CODEC driven by a frame signal synchronized with a PC clock) and a TEL side C
By using ODEC (CODEC driven by a frame synchronization signal synchronized with a transmission clock of a telephone switching network) and performing analog coupling, generation of noise has been avoided.

However, in this technique, the PC side CO
In order to control the cycle of the frame synchronization signal of the DEC, it is necessary to use a FIFO inside the device.
A circuit for constantly monitoring the amount of data stored in the memory is also required. Therefore, there is a problem that the scale of hardware increases.

[0005]

OBJECTS OF THE INVENTION The main object of the present invention is to provide a PC for a telephone switching network.
When a telephone terminal device for transmitting or receiving voice data between a PC and a telephone switching network connects the PC with a USB interface (asynchronous transfer mode) to transfer voice data, An object of the present invention is to provide a telephone terminal device in which generation of noise due to data slip is prevented by a circuit simplified as compared with the conventional technology.

[0006]

A telephone terminal device according to the present invention transmits or receives a voice signal as a digital signal between a PC and a telephone switching network, and performs connection between the PC and the telephone switching network. The communication system includes a USB interface and a communication interface that are operated by first and second clocks from the first and second CODECs, and the first clock has a clock generation unit that switches a plurality of clock sources having different speeds.

According to a preferred embodiment of the present invention,
The clock generation unit uses the SOF from the USB interface
Counter, a phone frame counter for counting the frame synchronization signal of the second CODEC, a comparator for comparing the counter values of these two counters, and a frequency selector for switching a plurality of clock sources based on the output of the comparator. . When converting a digital signal of a PC into an analog signal, a plurality of clock sources having different speeds are switched to achieve speed matching. The clock is switched based on the difference between the period of the frame synchronization signal on the PC side and the period on the telephone switching network side measured by the SOF counter and the telephone frame counter, and based on this difference. Further, the connection between the digital voice signal of the PC and the digital voice signal of the telephone switching network is performed by converting into an analog signal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a preferred embodiment of a telephone terminal device according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a preferred embodiment of a telephone terminal device according to the present invention and related devices. In FIG. 1, a telephone terminal device 10 is a USB terminal.
It is connected to a PC 5 via a bus and to a telephone main unit / station (hereinafter simply referred to as a main unit) 6 via a telephone exchange network. The telephone terminal device 10 includes a USB interface (I / F) 1, a communication interface 2, a first (or PC side) CODEC (encoder / decoder) 3, and a second
(Or main device side) It is composed of CODEC4. 1st C
The ODEC 3 supplies a first clock (CLK1) to the USB interface 1, and the second CODEC 4 supplies a second clock (CLK2) to the communication interface 2.

Hereinafter, each of the constituent elements 1 in the telephone terminal device 10 will be described.
4 will be described. USB interface 1 (not shown)
Is an interface having a USB controller for transmitting and receiving data between the PC 5 and the telephone terminal device 10 via USB. The communication interface 2 is connected to the main unit 6 via a telephone exchange network, and is an interface for transmitting and receiving D-channel data (control data) and B-channel data (voice data). 1st C
ODEC3 is a CODEC for A / D (analog / digital) conversion and D / A (digital / analog) conversion of B channel data transmitted / received to / from PC5.
A frame synchronization signal for D and D / A conversion is a PC
5 for the CODEC synchronized with the clock PC_CLK of No. 5
It is driven by a clock (CLK1). On the other hand, the second CODE
C4 transmits B channel data transmitted / received to / from main device 6 to A
A / D and CODEC for D / A conversion.
The frame synchronization signal for the D / A conversion is driven by a second clock (CLK2) synchronized with MasterCLK which is a clock of the main device 6.

Next, a feature of the telephone terminal device according to the present invention resides in a clock generation unit of the first (PC side) CODEC 3. The configuration of the clock generation unit 30 of the first CODEC 3 will be described with reference to the block diagram of FIG. The clock generator 30 includes a USB interface 20, a SOF counter 21, a TEL (telephone) frame counter 22, a comparison calculator 23, first to fourth frequency generators (or clock sources) 24 to 27, and a frequency selector 28. Have been.

In the clock generator 30 of the PC side CODEC 3 shown in FIG.
This is an SB communication interface. SOF counter 21
Counts the SOF detected by the USB interface 20. The TEL frame counter 22 counts the frame synchronization signal of the second (or TEL side) CODEC 4. The comparison calculator 23 compares the count values of the SOF counter 21 and the TEL frame counter 22 described above. The frequency selector 28 is connected to the comparison operator 23
Select the frequencies from the frequency generators 24 to 27 based on the output of. The first to fourth frequency generators 24 to 27 are:
It is a drive clock source for the first (or) PC side CODEC3.

Here, the first to fourth frequency generators 24 to 24
The frequency 27 is selected and set in the following relationship. First frequency 24 <second frequency 25 <third frequency 26
<Fourth frequency 27> Here, the first frequency means the frequency generated by the first frequency generator 24. The same applies to the second to fourth frequencies. The initial value of the first clock (CLK1) for operating the USB interface 1 is:
It is assumed that the third frequency 26 is selected, and normal frequency switching is performed by reciprocating between the third frequency 26 and the second frequency 25.

Next, the operation of the telephone terminal device 10 according to the present invention shown in FIGS. 1 and 2 will be described with reference to FIGS. Here, FIG. 3 shows a configuration diagram of the SOF counter 21 and the TEL frame counter 22 of the clock generation unit 30 shown in FIG. FIG. 4 is a view for explaining a count pattern comparison calculation operation by the comparison calculator 23 shown in FIG. The SOF counter 21 and the TEL frame counter 22 shown in FIG. 3 describe the corresponding counters 21 and 22 shown in FIG. 2 in detail.

The SOF counter 21 shown in FIG.
Is a two-bit (bit 0 and bit 1) counter that performs a binary count-up when a is detected. TEL
The frame counter 22 outputs the second (or TEL side) COD
This is a 5-bit (bit0 to bit4) counter for binary counting the EC4 frame synchronization signal. SOF
Is detected at a period of about 1 ms, and the second (TEL side) COD
The EC4 frame synchronization signal is generated at a period of 125 μs. If the SOF is detected accurately at a period of 1 ms and is synchronized with the frame synchronization signal of the second (TEL side) CODEC 4, the count in the dotted frame shown in FIG. However, SOF and the second
(TEL side) Since the frame synchronization signal of the CODEC 4 is asynchronous and the SOF generation cycle includes an error, the count-up in the dotted frame described above is shifted with time. Since this shift causes the slip of the B channel data, the drive clock of the first (PC side) CODEC 3 is controlled to absorb the shift. The comparison operation in the dotted frame is T
When the bit 3 of the EL frame counter 22 changes (every 1 ms cycle), the counter value of the SOF counter 21 is latched.

Next, referring to FIG.
The frequency switching operation based on the comparison operation result of the comparison operation unit 23 at 0 will be described. SOF counter 21 and TEL
Based on the comparison operation result of the frame counter 22, the frequency is determined by the following algorithm. The counter value in FIG. 4 is obtained by converting the counter value in FIG. 3 into a decimal value. When the pattern in the solid line frame matches (when the comparison operation matches three times in succession), the SOF is applied to the frame signal of the second (TEL side) CODEC 4 with reference to the immediately preceding pattern (in the dotted frame). Time delay or advance. Then, the drive clock frequency of the first (PC) CODEC 3 is switched so that the B channel data does not slip.

First, in the case of the SOF count pattern A, the SOF count 21 is changed to the second (TEL side) CODE.
Since the count is earlier than the count of eight C4 frame signals, the frequency is switched to one step earlier than the immediately preceding frequency. next,
In the case of the SOF count pattern B, since the SOF count is slower than the count of eight frame signals of the second (TEL side) CODEC 4, the frequency is switched to a frequency one step slower than the immediately preceding frequency.

If the above and are described by a ternary logical expression, the following expression is obtained. TEL frame counter value = SOF counter value → frequency is not changed. TEL frame counter value = 1 + SOF counter value → Switch to frequency one step earlier. TEL frame counter value + 1 = SOF counter value → Switch to frequency one step slower.

Since there are three types of patterns (three consecutive matches) in the solid line frame in FIG. 4, they are shown in FIG. FIG.
Indicates the above-described matching condition, the SOF counter value immediately before the matching condition, and the frequency correspondence.

The configuration and operation of the preferred embodiment of the telephone terminal device according to the present invention have been described above in detail. However, it should be understood that such example embodiments are merely illustrative of the present invention. Without departing from the spirit of the invention,
Those skilled in the art will readily understand that various modifications can be made depending on the specific application.

[0021]

As is apparent from the above description, according to the telephone terminal device of the present invention, a simple circuit can be used even when the clock of the PC and the clock of the telephone exchange network are not synchronized or when there is an error in the SOF. It is possible to transmit and receive voice data using a built-in clock, which has a remarkable practical effect that a telephone terminal device of voice data without noise can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of a telephone terminal device and related systems according to the present invention.

FIG. 2 shows a first example of the telephone terminal device according to the present invention shown in FIG.
(PC side) FIG. 3 is a block diagram of a clock generation unit that drives a CODEC.

FIG. 3 is a configuration diagram of an SOF counter and a TEL frame counter shown in FIG. 2;

FIG. 4 is an explanatory diagram of a count pattern by a comparison calculator shown in FIG. 2;

FIG. 5 is an explanatory diagram of a coincidence pattern and a switching frequency in the clock generation unit of FIG. 2;

[Explanation of symbols]

 1, 20 USB interface 2 Communication interface 3 First (PC side) CODEC 4 Second (TEL side) CODEC 5 PC 6 Telephone main device / station 10 Telephone terminal device 21 SOF counter 22 TEL frame counter 23 Comparative calculator 24 to 27 Frequency source (clock source) 28 Frequency selector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B077 AA14 GG32 NN02 5B079 BA01 BB10 BC10 DD03 5K027 BB05 BB07 HH26 KK02 5K101 KK02 KK20 LL01 SS06 UU08

Claims (5)

[Claims] 1. A telephone terminal device for transmitting or receiving a voice signal as a digital signal between a personal computer (PC) and a telephone exchange network, wherein each of the first and second terminals is connected to the PC and the telephone exchange network.
And a USB (Universal Serial Bus) interface and a communication interface operated by first and second clocks from the second CODEC.
A telephone terminal device comprising: a clock generation unit that switches a plurality of clock sources having different speeds. 2. The clock generating section includes: an SOF counter for counting SOF from a USB interface; a telephone frame counter for counting a frame synchronization signal of the second CODEC; a comparator for comparing the counter values of the two counters; 2. The telephone terminal device according to claim 1, further comprising a frequency selector for switching clocks from the plurality of clock sources according to an output of the comparison operation unit. 3. The method according to claim 2, wherein when converting the digital audio signal of the PC into an analog signal, the plurality of clocks having different speeds are switched to achieve speed matching.
A telephone terminal device according to item 1. 4. The switching of the clock is performed by the SOF counter and the telephone frame counter.
4. The method according to claim 3, wherein a period difference between the frame synchronization signals on the communication side and the telephone network is measured, and the measurement is performed based on the difference.
A telephone terminal device according to item 1. 5. The telephone terminal device according to claim 1, wherein the connection between the digital voice signal of the PC and the digital voice signal of the telephone switching network is performed by converting the digital voice signal into an analog signal.