JP2003502915A - Line driver for POTS, xDSL or integrated POTS / xDSL interface - Google Patents

Abstract

(57) Abstract: A driver circuit (180) comprises a transformer having a next winding (106, 108) coupled to a subscriber line and a secondary winding (104) coupled to an interface circuit; A feedback circuit coupling the next winding to the secondary winding to provide a predetermined impedance match between the lines over a predetermined frequency band of the driver circuit. In a preferred embodiment, the interface circuit is an integrated line card providing POTS and ADSL.

Description

Detailed Description of the Invention

The present invention relates to voice and data communication systems, and more particularly to interface circuits for coupling a combination of telephone and high speed data communication functions to a two wire telephone line.

BACKGROUND OF THE INVENTION As the Internet becomes more and more popular, there is a demand for corresponding high-speed digital transmission to local subscriber lines of telephone companies. The line is a twisted pair copper telephone line. Lines have different distances, diameters, life spans, and transmission characteristics depending on the network. These lines have natural conduits (nat) to provide high-speed digital communication services due to the already existing large-scale facility infrastructure.
ural coduit). Digital transmission systems on these lines typically use AD
It includes asymmetric, symmetric, high speed and very high speed digital subscriber lines, known as SL, SDSL, HDSL and VDSL, respectively. These and other similar protocols are commonly known as xDSL.

Among these xDSL types, ADSL is intended to coexist with traditional voice services by using different frequency spectra on the line.
In the future, multiple different transmission schemes will be used in different frequency bands on the same line, but these transmission schemes will include traditional analog voice services as well as current and emerging forms of xDSL. Let's do it. In today's ADSL systems, the plain old telephone service (POTS) is 0 and 4 kHz for data over telephone lines.
, And ADSL uses a frequency spectrum between 30 kHz and 1.1 MHz. This is schematically shown in FIG. ADSL also transmits the frequency spectrum upstream (subscriber to CO) transmission in the low frequency band, typically 30 kHz to 138 kHz, and typically 138 kHz to 550 kHz.
Alternatively, it is divided into downstream transmissions in the higher frequency band of 1.1 MHz. ADSL is
It uses a discrete multitone (DMT) multicarrier technique that divides the available bandwidth into subchannels of approximately 4 kHz.

The architecture, interfaces and protocols for a telecommunications network incorporating an ADSL modem are shown in FIG. 1 (b). The elements are
The central office side 4 is equipped with a plurality of ATU-C2 or ADSL modems. ATU
-C2 can be integrated in the access node 6, which is the confluence point for the wideband data 8 and the narrowband data 10. Wideband and narrowband in this context refer to switching systems for data rates above 1 Mbps and switching systems for data rates below 1 Mbps, respectively. The access node 6 can be located at a central office or at a remote location. The remote access node is also delimited from the central access node. The plurality of ATU-C 2 are coupled to the telephone line 14 via the splitter 12. Customer line 14 is also coupled to telephone line 14 via splitter 12. The customer line 14 is coupled via a splitter 12 to a customer ATU-R 16 or ADSL modem which can be integrated into a device (SM) which is a device performing the terminal adaptation function. Examples are set top boxes, PC interfaces or LAN routers. PSTN (Public Switched Telephone Network) 18 for subscriber telephone 20
The line 14 is shared via a splitter 12 that isolates the TS from the ADSL modem.

As shown in FIG. 2, the analog splitter 24 provides the filtering needed to separate the POTS and ADSL bands before they are input to their respective transceivers. Typically, the splitter 34 comprises a low pass filter 36 between the telephone and the line and a high pass filter between the ADSL transceiver and the line. The low frequency components output from the LPF are sent to a normal telephone line card. These analog signals are converted into digital signals by A / D and CODEC and encoded as PCM signals. These signals are then sent to other P's.
It may be combined with the CM signal and sent to other central offices or switching networks. Splitters are usually very large and expensive components. Several solutions have been proposed so far to eliminate the splitter. For example, US Pat. No. 5,757,803 describes an improved splitter, US Pat.
89856 is an integrated ADSL line with digital splitter
The card is listed.

It is generally believed that the function of a POTS splitter is to separate different frequency bands and send them to individual transceivers. The actual function is more complex, addressing the need to provide the correct impedance at different frequencies in order to allow the signal to propagate properly and meet the relevant specifications. Conventional POTS splitters cannot eliminate or reduce the effects of interference from POTS and ADSL equipment, but a properly designed interface eliminates these problems by adding low-pass or high-pass filters in the signal path. be able to.

Matching the line interface card to the line is not very complicated in the low frequency band. Various circuits for achieving such matching are described in US Pat.
515433. However, these circuits are limited when broadband matching is required. The present invention is therefore aimed at alleviating some of the above-mentioned drawbacks.

SUMMARY OF THE INVENTION The present invention provides a solution to the common problems required for POTS splitters in integrated line interface modules, especially in central offices or "head ends". Is intended. An advantage of the present invention is that telephones and data or different types of data use different frequency spectra on a two-wire communication line, between telephones and digital subscriber line ("DSL") services or other communication systems. May be used for combinations.

Another advantage of the present invention is that it eliminates the conventional POTS splitter and frequency dependent impedance synthesis is implemented by highly integrated circuits using either digital, analog or a combination of digital and analog means. To provide broadband line drivers and terminations that enable Another advantage of the present invention is that it minimizes power, cost and size to carry integrated voice and data.

According to the present invention, a transformer having a primary winding coupled to the subscriber line and a secondary winding coupled to the interface circuit, and a predetermined impedance matching between the interface circuit and the line is provided for the circuit. A drive circuit is provided that includes a feedback circuit that couples the primary winding to the secondary winding to provide over a frequency band.

These and other features of the preferred embodiments of the present invention will become more apparent in the following detailed description, in which reference is made to the accompanying drawings.

[0012]     (Description of preferred embodiments)   In the description below, like numerals refer to like structures in the figures.

According to the prior art, referring to FIG. 2, a DSL central office system is designated by the numeral 20. The system comprises an ADSL transceiver 21 for processing digital data, a POTS splitter 34 and a POTS transceiver incorporating a SLIC (subscriber line interface circuit) 26 and a CODEC 22 for processing voice data. Separate the audio signal and send it to SLIC and COD
A POTS splitter 24, which supplies the EC 22 and high frequency data signals to the ADSL transceiver 21, is coupled to a subscriber line 28. The ADSL transceiver includes a DSL baseband circuit 31, DS coupled to a wideband data path.
It includes a DSL analog front end (AFE) 33 powered from L baseband circuitry and coupled to splitter 24 via a line driver. ADSL transceivers provide bidirectional communication between wideband data paths and lines. Digital processing circuits provide digital signal processing functions such as modulation, echo cancellation and equalization. AFEs typically include both transmit and receive channels. The transmit channel includes a wideband data bus, a digital-to-analog converter (D / A) coupled to the transmit filter, followed by a line driver coupled to the splitter through a hybrid. The receive channel includes a hybridly coupled receive filter, a programmable gain amplifier driving an analog-to-digital converter that outputs the digital signal to a digital processing unit on a wideband data path. Both the transmit and receive channels are coupled to a splitter which is coupled to the line by a transformer.

As mentioned in the background of the invention, there are many drawbacks with this arrangement.

The present invention uses a common line driver 46 for voice / audio, as schematically illustrated in FIG.
It includes a modification to this conventional configuration by integrating a data analog front end (AFE) 42 and a voice / data baseband 44. Therefore,
The integrated unit provides bidirectional communication between the line and the system bus or system buses carrying ADSL and PCM data. If this integrated approach is taken, the frequency dependent termination in each frequency band is
2, must be synthesized by baseband 44 or a combination of the two. Moreover, the line driver must provide a fairly flat response over the entire range of frequencies, which would be 200 kHz to 1.1 MHz in integrated POTS and ADSL applications.

Referring to FIG. 5, for voice and data requests according to an embodiment of the present invention,
The integrated line interface module 40 of FIG.
level) block diagram is shown in detail. The AFE 42 may include a line driver 52 coupled to the line, impedance combining, and includes a wideband AFE 54 coupled to the line driver 52 and an A / D and D / A converter 56. As such, the AFE may provide bidirectional communication between the line and the digital processing unit 44, and may provide frequency dependent impedance synthesis in whole or in part.

The digital processing section 44 may include a digital impedance combining unit coupled to the AFE 42. The unit provides either the total or partial impedance synthesis required for the complex system and provides frequency dependent filtering and equalization. Composite signal is voice CODEC
60 and an ADSL modem 62 coupled to a baseband processing unit that comprises one or more DSP-based processing elements. The baseband processing unit is coupled to one or more system buses that carry high speed ADSL data and PCM voice signals.

A feature of the present architecture is a wideband line driver circuit that enables the integration of complex impedance combining functions into highly integrated digital or analog circuits. In a preferred embodiment, the line driver has a DC power supply capability of up to 100 mA, a flat or near flat frequency response between 200 Hz and 1.1 MHz or higher, an AC signal swing up to 22 V peak, and low power consumption. And provide.

One technique in the prior art is wideband SLIC implemented with high voltage integrated circuit technology.
Is to use. In this approach, the SLIC must carry both DC line current, low frequency audio signals and high frequency data signals. This approach suffers from a variety of problems including excessive power consumption due to the large signal current and signal voltage headroom required for driver amplifiers, difficulty in implementing in silicon technology, and limited line range due to 48V battery power. There is.

One preferred approach is to use a transformer-based drive circuit that couples the integrated voice / xDSL unit to the line. The main difficulty when using a transformer-based solution is caused by transformer roll-off at low and high frequencies due to the combination of primary inductance, leakage inductance and interwinding capacitance and core limitations.

Referring to FIGS. 6 (a) -6 (f), various transformer-based drive circuits for coupling an integrated voice / xDSL unit to a line are shown. By using feedback techniques to linearize circuit performance in this application, everything is aimed at avoiding problems caused by transformer limitations.

FIG. 6 (b) shows a transformer configuration with a feedback loop that overdrives the input. In Figure 6 (c), the transformer pair comprises a high frequency feedforward on the second transformer. FIG. 6 (d) is a modification of the configuration of FIG. 6 (c) with high frequency feedforward with capacitors. Finally, as shown in FIG.
), Two transformers are provided with separate drives for each.

7 (a) -7 (f), the broadband transformer has a split primary with primary and secondary windings having the polarities shown. The transformer has a single secondary winding 104. In this specification, the primary side is the line side of the line-fed transformer,
The secondary side refers to the voice / xDSL modem side of the transformer. The primary to secondary turns ratio of the transformer is preferably about 1: 1 but other ratios are possible. Typically, the line transformer, which must carry a magnetizing inductance of 100mH to 2H while carrying 20mA to 100mA in the primary winding, is 1: 1. Normal AC voltage amplitude is 22 volts peak, and impedance seen on the line is about 900 in the voice band
ohms, about 100 ohms in the ADSL band.

Referring to FIG. 7 (a), an interface circuit (not shown) typically inputs V to a driver circuit 180 coupled to a twisted pair telephone line having TIP and RING conductors extending between the central office and the customer premises. supply _i . The drive circuit is
It includes a transformer with a pair of primary windings respectively coupled to the TIP and RING lines by respective line feed elements R _feed , which are typically 50 ohms. The other end of the primary winding is connected to a respective battery return or TIP DC and a talk battery or RING DC. On the secondary side of the transformer, the input voltage V _i is supplied to the respective ends of the secondary via respective inverting operational amplifiers.

In FIG. 7 (a), the primary winding 106 is coupled at one end to a feed resistor 107 that is coupled to one of the line conductors TIP, and the secondary winding 108 is a second line conductor RIN.
It is coupled to the feed resistor 110 which is coupled to G.

In FIG. 7B, the differential voltage on the primary side is detected and fed back to the secondary side. Feedback circuit, the primary side of the transformer, senses the differential output voltage V _o, by comparing the differential output voltage V _o and the desired output voltage V _i, the error signal to generate a feedback signal V _f Multiply with high gain and drive the secondary with signal V _f to provide enhanced drive for the transformer.

In FIG. 7C, the differential voltage on the primary side is detected and fed back to the secondary side. The feedback circuit senses the differential output voltage V _o at the primary side of the transformer, the differential output voltage V _o is compared with the desired output voltage V _i, a high gain error signal to produce a feedback signal V _f Drive the primary side of the transformer with V _f through a capacitor. The secondary side of the transformer is driven by the desired input voltage V _i .

In FIG. 7D, the differential voltage on the primary side is detected and fed back to the secondary side. The feedback circuit senses the differential output voltage V _o at the primary side of the transformer, the differential output voltage V _o is compared with the desired output voltage V _i, a high gain error signal to produce a feedback signal V _f And drive the primary side of the transformer with the complementary signal V _f through the respective capacitors. The secondary side of the transformer is also driven by the feedback signal V _f .

In FIG. 7E, the differential voltage on the primary side is detected and fed back to the secondary side. The feedback circuit senses the differential output voltage V _o at the primary side of the transformer, the differential output voltage V _o is compared with the desired output voltage V _i, a high gain error signal to produce a feedback signal V _f And drives the primary side of a second transformer coupled through a capacitor. The signal V _f drives the secondary of the second transformer, the secondary winding of the second transformer being capacitively coupled to the output signal V _o . The secondary side of the first transformer is driven by the desired input voltage V _i .

In FIG. 7F, the differential voltage on the primary side is detected and fed back to the secondary side. The feedback circuit senses the differential output voltage V _o at the primary side of the transformer, the differential output voltage V _o is compared with the desired output voltage V _i, a high gain error signal to produce a feedback signal V _f And drives the primary side of a second transformer coupled through a capacitor. The signal V _f drives the secondary of the second transformer, the secondary winding of the second transformer being capacitively coupled to the output signal V _o . The secondary side of the first transformer is driven by the output signal V _f .

FIG. 7 (g) is the same as FIG. 8 (f) except that an impedance is added between the next winding of the first transformer and the output voltage V _o . In this configuration, the two transformers can be configured to have a crossover frequency determined by the impedance in series with the two transformers and provide driving power in different frequency bands.

While the invention has been described with reference to certain specific embodiments, various modifications thereof can be made without departing from the spirit and scope of the invention as outlined in the claims appended hereto. It will be apparent to those skilled in the art.

[Brief description of drawings]

Figure 1a   It is a figure which shows the frequency spectrum of an ADSL system.

Figure 1b   1 is a schematic diagram of an ADSL system architecture.

[Fig. 2]   1 is a schematic diagram of a prior art ADSL modem.

[Figure 3]   1 is a schematic diagram of a prior art DSL transceiver.

[Figure 4]   1 is a schematic diagram of an ADSL modem according to an embodiment of the present invention.

[Figure 5]   FIG. 3 is a schematic block diagram of an ADSL modem according to an embodiment of the present invention.

FIG. 6a

FIG. 6f   3 is a schematic diagram of a drive circuit according to an embodiment of the present invention. FIG.

[Fig. 7a]

FIG. 7f   FIG. 7 is a detailed schematic circuit diagram of the circuits of FIGS. 6 (a) to 6 (f).

[Procedure amendment]

[Submission date] February 5, 2002 (2002.2.5)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Contents of correction]

Referring to FIGS. 6 (a) -6 ( e ), various transformer-based drive circuits for coupling an integrated voice / xDSL unit to a line are shown. By using feedback techniques to linearize circuit performance in this application, everything is aimed at avoiding problems caused by transformer limitations.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Contents of correction]

Referring to FIG. 7 (a), the interface circuit (not shown) typically inputs V to a driver circuit 180 coupled to a twisted pair telephone line having a tip and ring conductor extending between the central office and the customer premises. supply _i . Drive circuit is generally the respective line feeding element R _feed is 50ohm, comprises a transformer having a pair of primary windings coupled respectively to the chip and-ring conductor. The other end of the primary winding is connected to the respective battery return or chip DC and talk.
k) -Connected to battery or ring DC. On the secondary side of the transformer, the input voltage V _i is supplied to the respective ends of the secondary via respective inverting operational amplifiers.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Contents of correction]

In FIG. 7A, a primary winding 106 is coupled at one end to a feed resistor 107 that is coupled to one of the line conductor chips , and a secondary winding 108 is coupled to the second line conductor ring . Is connected to the power supply resistor 110 that is connected.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Contents of correction]

FIG. 7 (g) is the same as FIG. 7 (f) except that an impedance is added between the next winding of the first transformer and the output voltage V _o . In this configuration, the two transformers can be configured to have a crossover frequency determined by the impedance in series with the two transformers and provide driving power in different frequency bands.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Contents of correction]

[Brief description of drawings]

Figure 1a   It is a figure which shows the frequency spectrum of an ADSL system.

Figure 1b   1 is a schematic diagram of an ADSL system architecture.

[Fig. 2]   1 is a schematic diagram of a prior art ADSL modem.

[Figure 3]   1 is a schematic diagram of a prior art DSL transceiver.

[Figure 4]   1 is a schematic diagram of an ADSL modem according to an embodiment of the present invention.

[Figure 5]   FIG. 3 is a schematic block diagram of an ADSL modem according to an embodiment of the present invention.

FIG. 6a

FIG. 6e   3 is a schematic diagram of a drive circuit according to an embodiment of the present invention. FIG.

[Fig. 7a]

7f is a detailed schematic circuit diagram of the circuit of FIGS. 6 (a) -6 ( e ). FIG.

[Procedure correction 6]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Contents of correction]

Figure 1a

Figure 1b

[Fig. 2]

[Figure 3]

[Figure 4]

[Figure 5]

FIG. 6a

FIG. 6b

FIG. 6c

FIG. 6d

FIG. 6e

FIG. 7a

FIG. 7b

FIG. 7c

FIG. 7d

[Fig. 7e]

FIG. 7f

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, MZ, SD, SL, SZ, TZ, UG , ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, C H, CN, CR, CU, CZ, DE, DK, DM, DZ , EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, K G, KP, KR, KZ, LC, LK, LR, LS, LT , LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, RU, S D, SE, SG, SI, SK, SL, TJ, TM, TR , TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (18)

[Claims] 1. A transformer having (a) a primary winding coupled to a subscriber line and a secondary winding coupled to an interface circuit; and (b) a predetermined impedance matching between the interface circuit and the line. A feedback circuit that couples the primary winding to the secondary winding to provide over a predetermined frequency band of the circuit. 2. The interface circuit is a POTS protocol and xDS.
The driver of claim 1, which provides the L protocol. 3. The feedback circuit converts a differential output voltage V _o on the line to an input voltage V _o from the interface circuit to generate an error signal V _f that drives the primary winding of the transformer. The driver of claim 1 including a comparator that compares with _i . 4. The driver according to claim 1, wherein the predetermined frequency band includes a high frequency band for data communication and a low frequency band for voice communication. 5. The driver circuit of claim 1, wherein the transformer includes first and second transformers driving first and second type signals on the line from a common feed point, respectively. 6. The driver of claim 5, wherein the first type of signal comprises a POTS signal and the second type of signal comprises a DSL signal. 7. The driver of claim 1, wherein the feedback circuit provides compensation for transformer roll off. 8. A feedback circuit compares the differential output voltage on the line with an input voltage V _i to produce a feedback signal V _f, and a DC isolation circuit coupling the feedback signal to the line. The driver of claim 1, including: 9. The driver according to claim 8, wherein the DC isolation circuit is a capacitor. 10. The driver of claim 8, wherein the DC isolation circuit couples the feedback signal V _f to the secondary side of the transformer. 11. The driver of claim 8, wherein the DC isolation circuit is a third transformer. 12. The driver of claim 11, wherein the third transformer is capacitively coupled to the line. 13. The driver of claim 11 including a line impedance element coupled between the secondary winding and the line. 14. The driver of claim 11, wherein the third transformer couples a feedback signal V _f to the secondary winding of the first transformer. 15. The driver of claim 14, wherein the third transformer is also capacitively coupled to the line. 16. The driver of claim 14 including a line impedance element coupled between the primary winding and the line. 17. The driver of claim 1, wherein the interface circuit is an integrated line card providing telephone and DSL. 18. The driver of claim 17, wherein the integrated line card includes an impedance combiner circuit that produces a desired termination impedance in each frequency band in which the card operates.