Direct digital access arrangement circuitry and method for connecting DSL circuitry to phone lines

Abstract

An isolation system is provided that is suitable for use in telephony, medical instrumentation, industrial process control and other applications. Preferred embodiments of the invention comprise a capacitive isolation barrier across which a digital signal is communicated. The system provides a means of communication across the isolation barrier that is highly immune to amplitude and phase noise interference. Clock recovery circuitry may be employed on one side of the isolation barrier to extract timing information from the digital signal communicated across the barrier, and to filter the effects of phase noise introduced at the barrier. Delta-sigma converters may be disposed on both sides of the isolation barrier to convert signals between analog and digital domains. An isolated power supply may also be provided on the isolated side of the barrier, whereby direct current is generated in response to the digital data received across the isolation barrier. A bidirectional isolation system is provided whereby bidirectional communication of digital signals is accomplished using a single pair of isolation capacitors. In preferred embodiments, the digital data communicated across the barrier consists of digital delta-sigma data signals multiplexed in time with other digital control, signaling and framing information. Finally, the isolation system may include a pulse transformer to accommodate ADSL circuitry, whereby power is transmitted through the pulse transformer.

Description

[0001] This is a continuation-in-part of U.S. Ser. No. 09 / 035,175 filed on Mar. 4, 1998 which is a continuation-in-part of U.S. Ser. Nos. 08 / 841,409, 08 / 837,702 and 08 / 837,714 all filed on Apr. 22, 1997. Further, the following U.S. patent applications filed Mar. 4, 1998, Ser. No. 09 / 034,687, entitled “Digital Isolation System With Data Scrambling” by George Tyson Tuttle et al; Ser. No. 09 / 034,456, entitled “Digital Isolation With ADC Offset Calibration; by Andrew W. Krone et al.; Ser. No. 09 / 034,455, entitled “Ring-Detect Interface Circuitry and Method for a Communication System” by Timothy J. Dupuis et al.; Ser. No. 09 / 035,779, entitled “Call Progress Monitor Circuitry and Method for a Communication System” by Timothy J. Dupuis et al.; Ser. No. 09 / 034,683, entitled “External Resistor and Method to Minimize Power Dissipation in DC Holding Circuitry for a Communication System” by Jeffrey W. Scott et al.; Ser. No. 09 / 034,620, entitled “Caller ID Circuit Powered Through Hookswitch Devi...

AI Technical Summary

Benefits of technology

[0013] The above-referenced deficiencies in the prior art are addressed by the present invention, which provides a reliable, inexpensive, lightweight isolation system that is substantially immune to noise that affects the timing and / or amplitude of the signal that is transmitted across the isolating element, thus permitting an input signal to be accurately reproduced at the output of the isolation system.

Problems solved by technology

However, analog signal communication through a transformer is subject to low frequency bandwidth limitations, as well as distortion caused by core nonlinearities.

Further disadvantages of transformers are their size, weight and cost.

However, two separate pulse transformers are disclosed for bidirectional communication with this technique, resulting in a cost disadvantage.

Another disadvantage of transformer coupling is that additional isolation elements, such as relays and opto-isolators, are typically required to transfer control signal information, such as phone line hookswitch control and ring detect, across the isolation barrier, further increasing the cost and size of transformer-based isolation solutions.

The disadvantage of this technique is that the analog communication, although differential, is not robust.

Mismatches in the differential components allow noise signals, which can capacitively couple into the isolation barrier, to easily corrupt both the amplitude and timing (or phase) of the analog modulated signal, resulting in unreliable communication across the barrier.

This scheme also requires separate isolation components for control signals, such as hookswitch control and ring detect, which increase the cost and complexity of the solution.

Furthermore, since capacitively coupled noise can cause timing (or phase) errors of voltage transitions in addition to amplitude errors, these modulation schemes remain sensitive to noise interference at the isolation barrier.

Consequently one disadvantage of this approach is that noise capacitively coupled at the isolation barrier can cause clock signal timing errors known as jitter, which corrupts the recovered analog signal and results in unreliable communication across the isolation barrier.

Reliable signal communication is further compromised by the sensitivity of the single ended signal transfer to voltages that exist between the isolated circuit sections.

Further disadvantages of the method described in this data sheet are the extra costs and board space associated with other required isolating elements, including a separate high voltage isolation capacitor for the clock signal, another separate isolation capacitor for bidirectional communication, and opto-isolators and relays for communicating control information across the isolation barrier.

As described, the modulation scheme encodes the signal information into on / off transitions of the LED at precise moments in time, thereby becoming susceptible to the same jitter (transition timing) sensitivity as the capacitive isolation amplifier modulation schemes.

In either case, no mechanism is provided for jitter insensitive communication of the ADC clock, which is required for reliable signal reconstruction, across the isolation barrier.

Some further disadvantages of optical isolation are that opto-isolators are typically more expensive than high voltage isolation capacitors, and they are unidirectional in nature, thereby requiring a plurality of opto-isolators to implement bidirectional communication.

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