Method and apparatus for isolation in a data access arrangement using analog encoded pulse signaling

A method for transferring information from a telephone line pair across a capacitive isolation barrier, the method comprising the steps of:

• receiving an analog receive data signal from the telephone line pair;
• pulse-width-modulation (PWM) encoding the received analog receive data signal to a PWM encoded data signal that directly represents the received analog data signal;
• driving the PWM encoded data signal across the capacitive isolation barrier;
• receiving the PWM encoded data signal across the capacitive isolation barrier;
• and decoding the received PWM encoded data signal,
• where the step of pulse-width-modulation (PWM) encoding the received analog receive data signal further comprises PWM encoding the received analog data signal to a PWM encoded data signal in an off-hook state and the method further includes the steps of:
• converting the received analog receive data signal to a frequency encoded data signal in an on-hook state;
• receiving the frequency encoded data signal across the capacitive isolation barrier;
• and
• decoding the received frequency encoded data signal into a digital count value during the on-hook state.

An isolation circuit, the circuit comprising:

• a single-ended driver, the driver having an input terminal for receiving a first data signal and an output terminal for outputting the first data signal to a first terminal of a first isolation capacitor, the driver being disposed in a line side circuit and configured to operate from a line side supply voltage, wherein the driver has another input terminal for receiving a reference voltage that is substantially half of the line side supply voltage;
• a hysteresis amplifier, the hysteresis amplifier having a non-inverting input terminal, an inverting terminal, and an output terminal, the hysteresis amplifier being disposed in a modem side circuit and configured to operate from a modem side supply voltage, where the non-inverting terminal is configured to receive the first data signal from a second terminal of the first isolation capacitor, and where the inverting terminal is configured to be coupled to a first terminal of a second isolation capacitor;
• a first resistor coupled between the non-inverting input terminal of the hysteresis amplifier and a reference circuit node configured to receive a modem side reference voltage;
• a second resistor coupled between the inverting input terminal of the hysteresis amplifier and the reference circuit node;
• and
• a third resistor configured to be coupled between a second terminal of the second isolation capacitor and another circuit node configured to receive a line side reference voltage.

An isolation circuit, the circuit comprising:

• a single-ended driver, the driver having an input terminal for receiving a data signal from a line pair and an output terminal for outputting the data signal to a first terminal of an isolation capacitor, the driver being configured to operate from a first power supply voltage obtained from the line pair, wherein the driver has another input terminal for receiving a reference voltage that is substantially half of the first power supply voltage;
• a hysteresis amplifier having a non-inverting and an inverting input terminal and an output terminal, where the non-inverting input terminal of the amplifier is configured to be coupled to a second terminal of the isolation capacitor, the amplifier being configured to operate from a second power supply voltage;
• a first resistor coupled between the inverting input terminal of the amplifier and a circuit node configured to receive a reference voltage;
• and
• a second resistor coupled between the non-inverting input terminal of the amplifier and the circuit node configured to receive a reference voltage.

An isolation circuit, the circuit comprising:

• a driver, the driver having an input terminal for receiving a data signal from a line pair and an output terminal for outputting the data signal to a first terminal of an isolation capacitor, the driver being configured to operate from a first power supply voltage obtained from the line pair;
• a hysteresis amplifier having a non-inverting and an inverting input terminal and an output terminal, where the non-inverting input terminal of the amplifier is configured to be coupled to a second terminal of the isolation capacitor, the amplifier being configured to operate from a second power supply voltage;
• a first resistor coupled between the inverting input terminal of the amplifier and a circuit node configured to receive a reference voltage;
• a second resistor coupled between the non-inverting input terminal of the amplifier and the circuit node configured to receive a reference voltage;
• a pulse-width-modulation (PWM) encoder disposed between the line pair and the driver for PWM encoding the data signal to produce a PWM encoded data signal for input to the driver, the PWM encoder having an input terminal for receiving the data signal and an output terminal coupled to the input terminal of the driver for outputting the PWM encoded data signal to the driver;
• a PWM decoder for decoding the PWM encoded data signal and output the data signal, the PWM decoder having an input terminal for receiving the PWM encoded data signal from the output terminal of the amplifier and an output terminal for outputting the data signal;
• a voltage-to-frequency converter (VFC) disposed between the line pair and the driver and configured to convert the data signal to a frequency encoded signal;
• a VFC decoder configured to receive the frequency encoded signal and decode the frequency encoded signal to generate a digital count value;
• and
• a processor for receiving the digital count value and performing at least one of ring detection, on-hook call monitoring, on-hook line voltage measurement, off-hook holding circuits, off-hook 2–4 wire hybrid, off-hook transmit and receive audio, and hook control.