DSP based SLIC architecture with current-sensing voltage synthesis impedance matching and DC feed control

A method of interfacing a telephony device to a communication medium comprising outputting signals to a telephony line with a composite differential MOSFET-bipolar driver stage, each side of the composite differential MOSFET-bipolar driver stage comprising:

• a MOSFET output driver;
• at least one first bipolar transistor coupled to the MOSFET output driver;
• a feedback path coupled between the first bipolar transistor and an output of the MOSFET;
• and
• a diode-connected second bipolar transistor coupled to a base of the first bipolar transistor, the diode-connected second bipolar transistor biasing the first bipolar transistor,
• wherein the first bipolar transistor biases the MOSFET to output a current, the feedback path provides an indication of the current from the MOSFET to the first bipolar transistor, and the first bipolar transistor adjusts the bias in response to the indication.

A telephony line interface circuit comprising a SLIC including a tip amplifier to drive a tip signal of a telephony line, and a ring amplifier to drive a ring signal of the telephony line, each of the tip and ring amplifiers comprising a composite differential MOSFET-bipolar driver stage with local feedback for bias stabilization, each side of the composite differential MOSFET-bipolar driver stage comprising:

• an input terminal;
• an output terminal;
• a feedback resistance coupled between the output terminal and a first node;
• a MOSFET current source coupled between the first node and the input terminal;
• at least one bipolar transistor coupled between the input terminal and the MOSFET current source, and coupled to the feedback resistance;
• and
• at least one diode coupled to the input terminal,
• wherein the at least one diode and the at least one bipolar transistor bias are coupled to the MOSFET to provide a current to the output terminal through the feedback resistance, thereby generating a feedback voltage across the feedback resistance, and
• wherein the at least one bipolar transistor adjusts the bias to the MOSFET in response to the feedback voltage.

A telephony line interface circuit, comprising:

• a SLIC including an operational amplifier having a composite differential MOSFET-bipolar symmetry complimentary driver stage with local feedback for bias stabilization, the driver stage comprising:
• first and second input terminals;
• at least one diode coupled between the first and second input terminals;
• an output terminal;
• a first feedback resistance coupled to the output terminal;
• a first MOSFET current source coupled to the first feedback resistance;
• a first set of one or more bipolar transistors coup led between the first input terminal and the first MOSFET;
• a second feedback resistance coupled to the output terminal;
• a second MOSFET current source coupled to the second feedback resistance;
• a second set of one or more bipolar transistors coupled between the second input terminal and the second MOSFET,
• wherein the at least one diode and the first and second sets of at least one bipolar transistor bias the first and second MOSFET current sources in response to first and second signals provided to the first and second input terminals, respectively, to provide current to the output terminal through the first and second feedback resistance, thereby generating first and second feedback voltages across the first and second feedback resistances, and
• wherein the first and second sets of at least one bipolar transistor adjust the bias to the first and second MOSFET current sources, respectively, in response to the feedback voltages;
• and
• a CODEC coupled to the SLIC.

A method of interfacing a telephony line to a communications medium, comprising:

• converting digital data from the communications medium to analog signals;
• and
• outputting the analog signals to the telephony line with a composite differential MOSFET-bipolar driver stage, the composite MOSFET-bipolar driver stage including:
• a MOSFET output driver;
• at least one first bipolar transistor coupled to the MOSFET output driver;
• a feedback path coupled between the first bipolar transistor and an output of the MOSFET;
• and
• a diode-connected second bipolar transistor coupled to a base of the first bipolar transistor, the diode-connected second bipolar transistor biasing the first bipolar transistor,
• wherein the first bipolar transistor biases the MOSFET to output a current, the feedback path provides an indication of the current from the MOSFET to the first bipolar transistor, and the first bipolar transistor adjusts the bias in response to the indication.