Modem with digital isolation

• US 5,369,666 A
• Filed: 06/09/1992
• Issued: 11/29/1994
• Est. Priority Date: 06/09/1992
• Status: Expired due to Term

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Rockwell International Corporation
• Inventors: Rahamim, Raphael, Folwell, Dale E.
• Primary Examiner(s): Dwyer, James L.
• Assistant Examiner(s): WEAVER, SCOTT LOUIS
• Application Number:
  US07/895,968
• Time in Patent Office: 903 Days
• Field of Search: 379/95, 379/98, 379/412, 379/410, 375/8, 375/34, 370/85.1, 370/94.1, 370/56, 361/413, 378/110
• US Class Current: 375/222
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors

Abstract

The MODEM WITH DIGITAL ISOLATION removes the relatively large heavy isolation transformer from the Data Access Arrangement and substitutes two tiny pulse transformers between the Integrated Analog and Digital Signal Processor with multiplexers and demultiplexers to eliminate analog distortion and multiple leads, and to accommodate Lap Top/Palm Top computers, while enhancing data speeds. The combination with surge protection enables both uncommon and common mode protection.

Claims

1. A modem without a conventional isolation transformer, comprising in combination:

a transformerless data access arrangement in communication with a telephone line system;

an integrated analog device;

a digital signal processor;

a microprocessor;

the integrated analog device connected to the data access arrangement and the microprocessor connected to the digital signal processor; and

,

pulse transformer means connected between the integrated analog device and the digital signal processor.

2. The modem of claim 1, wherein:

each of said integrated analog device and said digital signal processor comprising multiplexers and demultiplexers to insure that only digital signals are applied to said pulse transformer means, thereby eliminating analog distortion.

3. The modem of claim 1 wherein:

said pulse transformer means comprises a plurality of pulse transformers;

said plurality of pulse transformers each comprise a printed circuit board portion having a pair of spaced apart holes and a few turns of etched metal encircling each hole, thereby forming a coil around such hole;

a pair of U-shaped bars having legs on each end disposed across the spaced apart holes respectively on opposite sides of the printed circuit board with their legs respectively abutting in the holes to provide a magnetic gap path for the coil.

4. The method of eliminating a conventional transformer from a modem having a first section for receiving signals from, and transmitting signals to, a telephone line system, a second section for changing received signals from analog to digital and transmitted signals from digital to analog, a third section for processing digital signal and a fourth microprocessor section, comprising the steps of:

(a) introducing pulse transformers between the second and third sections for digital received and transmitted signals in lieu of the conventional transformer in the first section;

(b) multiplexing, in the second section, the received signals converted to digital form in the second section for application to at least one pulse transformer and demultiplexing said digital signals in the third section; and

(c) multiplexing, in the third section, the third section digital signals for transmission and applying them to at least one different pulse transformer and demultiplexing the digital signals for transmission in the second section, thereby eliminating any necessity for the conventional transformer from the first section, whereby distortion produced by the conventional transformer is eliminated.

5. The method of minimizing analog distortion in a modem connected to a telephone line system which comprises the steps of:

eliminating a conventional isolation transformer from a data access arrangement section;

changing a signal isolation from analog signal isolation to digital signal isolation by using one of magnetic and optical isolation; and

accomplishing said digital signal isolation between an integrated analog section and a digital signal processor section.

6. The method of claim 5, further comprising the step of:

converting an incoming analog signal from the telephone line system to a first serial stream of digital data prior to the digital isolation, and converting an outgoing digital signal into a second serial stream of digital data prior to digital isolation.

7. The method of claim 6, further comprising the step of:

providing the digital isolation by using at least one pulse transformer for each stream of data.

8. The method of surge protecting and achieving isolation in a digital portion of a modem which obviates a conventional isolation transformer, comprising the steps of:

establishing a path for analog signals from a telephone line system to a digital interface;

changing the analog signals to digital signals at the digital interface and passing the digital signals to a modem microprocessor;

establishing a digital signal path from the microprocessor to the digital interface;

passing the digital signals from the microprocessor through the digital interface;

changing the digital signals from the digital interface to analog signals and passing the analog signals to the telephone line system;

disposing a FET in one incoming telephone line for opening and closing said incoming telephone line;

sensing a surge voltage;

preventing said FET from conducting current when said surge voltage is sensed; and

,

maintained the preventing until the surge voltage has passed.

9. The method of surge protecting and minimizing analog distortion in a modem connected to a telephone line system which comprises the steps of:

eliminating a conventional isolation transformer from a data access arrangement, and;

changing signal isolation from analog signal isolation to digital signal isolation;

disposing a FET in a incoming telephone line for opening and closing said incoming telephone line;

sensing a surge voltage;

preventing said FET from conducting current when said surge voltage is sensed; and

,

maintaining the preventing until the surge voltage has passed.

10. The method of claim 9, wherein said digital signal isolation is accomplished by using one of magnetic and optical isolation.

11. The method of claim 10, further comprising the step of:

accomplishing said digital signal isolation between an integrated analog section and a digital signal processor section.

12. The method of claim 11, further comprising the step of:

converting a telephone line incoming analog signal to a first serial stream of digital data prior to the digital signal isolation, and converting an outgoing digital signal into a second serial stream of digital data prior to the digital signal isolation.

13. The method of claim 12, further comprising the step of:

providing said digital signal isolation by using at least one pulse transformer for each stream of data.

14. A modem without a conventional isolation transformer, comprising in combination:

a transformerless data access arrangement in communication with a telephone line system;

an integrated analog device;

a digital signal processor;

a microprocessor;

the integrated analog device connected to the data access arrangement and the microprocessor connected to the digital signal processor;

pulse transformer means connected between the integrated analog device and the digital signal processor;

TIP and RING leads for communicating between the telephone line system and the modem;

a FET connected to open and close one of said TIP and RING leads;

an ON/OFF HOOK circuit for supplying operating voltage to said FET when in an OFF HOOK mode;

a first circuit and a second circuit;

a flip-flop circuit for activating said first circuit in one condition and said second circuit in a second condition;

sensing means connected across said leads for activating said flip-flop circuit to said one condition upon sensing a surge voltage;

said first circuit preventing said FET from conducting current when said first circuit is activated; and

,

said second circuit resetting the flip-flop circuit after a predetermined time.

15. The modem of claim 14, further comprising:

multiplexer means in the integrated analog device for a received signal and demultiplexer means in the digital signal processor for the received signal;

further multiplexer means in the digital signal processor for a transmitted signal and further demultiplexer means in the integrated analog device for the transmitted signal, all of said transmitted signals and received signals passing through said pulse transformer means and being digital whereby analog signal distortion is avoided.

16. The modem of claim 15, further comprising:

clamp means for clamping a gate of said FET to ground in response to a surge voltage to prevent charge build-up on the gate.

17. The modem of claim 16, further comprising:

a first transistor connected to said flip-flop circuit to saturate when the flip-flop circuit is clocked;

a second transistor connected to the first transistor to turn on rapidly by the second transistor conducting; and

,

a shorting pathway closed by said first and second transistors from the RING lead to ground to discharge stray capacitance including any FET capacitance.

18. The modem of claim 17, further comprising:

a rectifier bridge circuit connected between the TIP and RING leads to insure positive voltage to a drain of the FET.

19. The modem of claim 18, further comprising:

a resistor-capacitor series circuit connected across the TIP and RING leads to serve as a dummy load for a RING signal.

20. The modem of claim 19 further comprising:

an electronic inductor for said modem including said first and second transistors and a parallel resistor-capacitor circuit.

21. The modem of claim 14, wherein:

said sensing means comprises a series circuit comprising of a capacitor and two resistors with a common point to both resistors being connected to a clock input of said flip-flop circuit, relative values of said resistors determining a point in the surge voltage which activates the flip-flop circuit.

22. The modem of claim 14 wherein:

said first circuit comprises a clamping transistor having its base connected to a Q output of the flip-flop circuit and being connected across a source-gate of said FET to ground a gate of the FET when the flip-flop circuit is clocked.

23. The modem of claim 14, wherein:

said second circuit comprises a resistor-capacitor network connected to a Q bar output of the flip-flop circuit the capacitor, and connected to a CLEAR input of the flip-flop circuit for discharging when the flip-flop circuit is clocked to maintain a gate grounding of the FET until after the surge voltage has disappeared.