As 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. Finally, 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.
This application is a continuation of U.S. patent application Ser. No. 08/837,702, filed Apr. 22, 1997, which became U.S. Pat. No. 5,870,046 on Feb. 9, 1999, and a continuation of U.S. Ser. No. 09/226,253 filed Jan. 7, 1999.
A sigma-delta analog-to-digital (A/D) converter comprising an input terminal, an adder, an integrator, a comparator and a flip flop circuit connected in series, with an output signal of the flip flop circuit being provided at an output terminal, and being fed back to the adder through a digital-to-analog (D/A) converter, so that the A/D converter provides a pulse density signal corresponding to a given input signal, wherein the comparator output is isolated from the input terminal of the flip flop circuit, and the output of the flip flop circuit is isolated from the D/A converter input terminal thereby achieving reduction of current consumption. The invention is useful in two wire vortex flowmeters, for example.
A bi-directional isolation scheme is described in which digital data, including clock information, may be communicated bi-directionally across a single isolation barrier without requiring a phase locked loop (PLL) based clock recovery procedure. In this way, the lead-time needed by the receiving circuit to recover the data clock signal may be reduced and the polarity (or 180.degree. phase) ambiguities often associated with PLL-based methods may be avoided.
A bi-directional isolation scheme is described in which digital data, including clock information, may be communicated bi-directionally across a single isolation barrier without requiring a phase locked loop (PLL) based clock recovery procedure. In this way, the lead-time needed by the receiving circuit to recover the data clock signal may be reduced and the polarity (or 180.degree. phase) ambiguities often associated with PLL-based methods may be avoided.
The present invention is directed toward a method and apparatus for transferring data across an isolation barrier using high speed analog encoded signals. A line side circuit interfaces with tip and ring contacts on one side of a capacitive isolation barrier that isolates the line side circuit from a modem side circuit. During an on-hook state, the line side circuit converts an analog line side voltage signal to a frequency signal and then encodes the frequency signal into a high frequency pulse-width-modulated (PWM) signal. The high frequency PWM signal is transmitted across the capacitive isolation barrier to the modem side circuit. During an off-hook state, the analog line side voltage is again encoded into a high frequency pulse-width-modulated (PWM) signal for transmission across the isolation barrier. The modem side circuit recovers the transmitted PWM signal and converts it into a digital count value that represents the amplitude of the analog voltage observed at the tip and ring. The digital count value may be directly processed by a processor on the modem side or may be converted back to an analog signal.
An improved line interface device and an improved xDSL modem for use in connecting data communications equipment to a xDSL line is disclosed. The line interface device provides the required isolation between the xDSL line and the communications equipment using optical isolation or capacitive techniques, as well as provides the power necessary to produce the transmit signal levels required by the communications services by utilizing a switching power supply deriving its power from a source isolated from the line, and including a transformer for isolating the source from the xDSL line. By switching at high frequencies the size of the transformer can be sufficiently small so that the interface device and supply can be provided in accordance with small form factor requirements.
