Squelch circuit

• US 5,003,556 A
• Filed: 06/30/1989
• Issued: 03/26/1991
• Est. Priority Date: 06/30/1989
• Status: Expired due to Term

• Current Assignee: Enterasys Networks Incorporated (Extreme Networks, Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Curtis, Robert A., Mallard, William C. Jr.
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US07/375,036
• Time in Patent Office: 634 Days
• Field of Search: 375/94, 375/106, 375/76, 375/104, 455/223, 455/218, 455/22 X, 455/303, 455/304, 307/358, 328/108, 328/109
• US Class Current: 375/351
• CPC Class Codes: H03G 3/345 Muting during a short period of time when noise pulses are detected, i.e. blanking H03G3/348 takes precedence
• CPC Class Codes: H03K 5/125 Discriminating pulses measuring characteristics of individual pulses G01R29/02; separation of synchronising signals in television systems H04N5/08
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04L 25/069 by detecting edges or zero crossings
• CPC Class Codes: H04L 7/046 using a dotting sequence

Abstract

A squelch circuit is disclosed that distinguishes between noise impulses and valid packets of data transmitted over a transmission line such as a twisted pair media within a local area network. The squelch circuit converts supplied data into a stream of positive and negative pulses and detects a sequence of positive and negative pulses quantified in time based on prior knowledge of the characteristics of a valid packet of data and permits the supplied data to pass if it has the characteristics of a valid packet of data or prohibits the supplied data from passing if it does not have the characteristics of a valid packet of data.

Claims

1. A squelch circuit for receiving the transmission of data over a data transmission line and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble and providing an enable signal; and

logic means for receiving said transmission and responsive to said enable signal for passing said transmission.

2. The squelch circuit of claim 1, wherein said data transmission line is twisted pair media.

3. A squelch circuit for receiving the transmission of data over a twisted pair media and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble and providing an enable signal;

said indication means preventing the generation of said enable signal when said first output signal comprises consecutive positive pulses or when said second output signal comprises consecutive negative pulses;

logic means for receiving said transmission and responsive to said enable signal from said indication means for passing said transmission;

third sensing means connected to said first and second sensing means for detecting the absence of both positive pulses of at least a predetermined positive threshold voltage level and negative pulses of at least a predetermined negative threshold voltage level for a third predetermined duration, and providing a reset signal indicative of the absence of said predetermined sequence to said indication means to prevent the generation of said enable signal;

fourth sensing means connected to said first sensing means for detecting positive pulses of at least a predetermined positive threshold voltage level and continuing for a fourth predetermined duration, and providing a reset signal indicative of the absence of said predetermined sequence to said indication means to prevent the generation of said enable signal; and

fifth sensing means connected to said second sensing means for detecting negative pulses of at least a predetermined negative threshold voltage level and continuing for a fifth predetermined duration, and providing a reset signal indicative of the absence of said predetermined sequence to said indication means to prevent the generation of said enable signal.

4. A method of distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting said noise, said data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said data transmission line;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for at least a first predetermined duration;

providing a first output signal when said positive pulses are detected;

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for at least a second predetermined duration;

providing a second output signal when said negative pulses are detected;

providing an enable signal when said first and second output signals are present in the same sequence as said predetermined sequence of positive and negative pulses indicative of the presence of said data stream preamble; and

passing said received transmission when said enable signal is present.

5. A method for distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting the passage of said noise, said data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said balanced line;

detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration;

providing a first output signal indicative of the presence of said positive pulses;

detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration;

providing a second output signal indicative of the presence of said negative pulses;

determining the presence of said first and second output signals and providing an enable signal indicative of the presence of said data stream preamble to pass said received transmission;

detecting the absence of both said positive pulses of at least a predetermined positive threshold voltage level and said negative pulses of at least a predetermined negative threshold voltage level for a third predetermined duration, and providing a disable signal indicative of the absence of said data stream preamble to inhibit the passage, of said received transmission;

detecting positive pulses of at least a predetermined positive threshold voltage level and continuing for a fourth predetermined duration, and providing said disable signal indicative of the absence of said data stream preamble to inhibit the passage of said received transmission;

detecting negative pulses of at least a predetermined negative threshold voltage level and continuing for a fifth predetermined duration, and providing said disable signal indicative of the absence of said data stream preamble to inhibit the passage of said received transmission; and

detecting said first output signal comprising consecutive positive pulses or said second output signal comprising consecutive negative pulses and providing said disable signal indicative of the absence of said data stream preamble to inhibit passage of said received transmission.

6. A squelch circuit for distinguishing between noise and a data stream in a transmission in a data processing network over twisted pair media, said data stream having a predetermined sequence of positive and negative pulses, comprising:

means for receiving said transmission and generating a series of positive and negative pulses;

first amplitude detection means for recognizing negative pulses of at least a first predetermined negative threshold voltage level and providing a first intermediate output signal;

second amplitude detection means for recognizing positive pulses of at least a predetermined positive threshold voltage level and providing a second intermediate output signal;

first duration detecting means for receiving said first intermediate output signal and detecting the continuance of said first intermediate output signal for a first predetermined duration, and providing a first output signal;

second duration detecting means for receiving said second intermediate output signal and detecting the continuance of said second intermediate output signal for a second predetermined duration, and providing a second output signal; and

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses and providing an enable signal to pass said received transmission.

7. The squelch circuit of claim 6 further comprising means responsive to said first and second intermediate output signals for recognizing an absence of both said positive and said negative pulses for a third predetermined duration, and providing a disable signal to said indication means to inhibit the passage of said received transmission.

8. The squelch circuit of claim 7 further comprising means responsive to said first intermediate output signal for recognizing negative pulses continuing for a fourth predetermined duration and providing a disable signal to said indication means to inhibit the passage of said received transmission.

9. The squelch circuit of claim 8 further comprising means responsive to said second intermediate output signal for recognizing positive pulses continuing for a fifth predetermined duration and providing a disable signal to said indication means to inhibit the passage of said received transmission.

10. The squelch circuit of claim 9 wherein said indication means inhibits the passage of said received transmission if said first output signal comprises consecutive positive pulses or if said second output signal comprises consecutive negative pulses.

11. The squelch circuit of claim of claim 6 further comprising means responsive to said first intermediate output signal for recognizing negative pulses of a third predetermined duration and providing a disable signal to said indication means to inhibit the passage of said received transmission.

12. The squelch circuit of claim 11 further comprising means responsive to said second intermediate output signal for recognizing positive pulses of a fourth selected duration and providing a disable signal to said indication means to inhibit the passage of said received transmission.

13. The squelch circuit of claim 12 wherein said indication means inhibits the passage of said received transmission if said first output signal comprises consecutive positive pulses or if said second output signal comprises consecutive negative pulses.

14. The squelch circuit of claim 16 further comprising means responsive to said second intermediate output signal for recognizing positive pulses of a third selected duration and providing a disable signal to said indication means to inhibit the passage of said received transmission.

15. The squelch circuit of claim 14 wherein said indication means inhibits the passage of said received transmission if said first output signal comprises consecutive positive pulses or if said second output signal comprises consecutive negative pulses.

16. The squelch circuit of claim 6 wherein said indication means inhibits the passage of said received transmission if said first output signal comprises consecutive positive pulses or if said second output signal comprises consecutive negative pulses.

17. The squelch circuit of claim 6 wherein said squelch circuit is located at one node of a plurality of nodes in said network and further comprises:

means for generating a transmit signal indicative of the concurrent transmission by said one node and at least one other node of said network;

said indication means responsive to said transmit signal for altering the duration of said predetermined sequence of positive and negative pulses.

18. A squelch circuit located at one node of a plurality of nodes in a data processing network for distinguishing between noise and a data stream in a transmission in said data processing network over twisted pair media, said data stream having a predetermined sequence of positive and negative pulses, comprising:

means for receiving said transmission and generating a series of positive and negative pulses;

first amplitude detection means for recognizing negative pulses of at least a first predetermined negative threshold voltage level and providing a first intermediate output signal;

second amplitude detection means for recognizing positive pulses of at least a predetermined positive threshold voltage level and providing a second intermediate output signal;

first duration detecting means for receiving said first intermediate output signal and detecting the continuance of said first intermediate output signal for a first predetermined duration, and providing a first output signal;

second duration detecting means for receiving said second intermediate output signal for a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses and providing an enable signal to pass said received transmission;

said indication means inhibiting the passage of said received transmission when said first output signal comprises consecutive positive pulses or said second output signal comprises consecutive negative pulses;

means responsive to said first and second output signals for recognizing the absence of both said positive and negative pulses for a third predetermined duration, and providing a disable signal to said indication means to inhibit the passage of said received transmission;

means responsive to said first intermediate output signal for recognizing negative pulses continuing for a fourth predetermined duration and providing a disable signal to said indication means to inhibit said passage of said received transmission;

means responsive to said second intermediate output signal for recognizing negative pulses continuing for a fifth predetermined duration and providing a disable signal to said indication means to inhibit said passage of said received transmission; and

means for generating a transmit signal indicative of the concurrent transmissions by said one node and at least one other node of said network;

said indication means responsive to said transmit signal for altering the duration of said predetermined sequence of positive and negative pulses.

19. A squelch circuit for receiving the transmission of data over a data transmission line and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble and providing an enable signal;

third sensing means connected to said first and second sensing means for detecting the absence of both positive pulses of at least a predetermined positive threshold voltage level and negative pulses of at least a predetermined negative threshold voltage level for a third predetermined duration, and providing a reset signal output to said indication means to prevent the generation of said enable signal; and

logic means for receiving said transmission and responsive to said enable signal for passing said transmission.

20. The squelch circuit of claim 19 further comprising fourth sensing means connected to said first sensing means for detecting positive pulses of at least a predetermined positive threshold voltage level and continuing for a fourth predetermined duration, and providing a reset signal output to said indication means to prevent the generation of said enable signal.

21. The squelch circuit of claim 20 further comprising fifth sensing means connected to said second sensing means for detecting negative pulses of at least a predetermined negative threshold voltage level and continuing for a fifth predetermined duration, and providing a reset signal output of said indication means to prevent the generation of said enable signal.

22. The squelch circuit of claim 21 wherein said indication means prevents the generation of said enable signal when said first output signal comprises consecutive positive pulses or when said second output signal comprises consecutive negative pulses.

32. The method of claim 21 further comprising the steps of:

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for a fifth predetermined duration, and providing a disable signal when said negative pulses continuing for a fifth predetermined duration are detected; and

,

inhibiting the passage of said received transmission when said disable signal is present.

33. The method of claim 32 further comprising the steps of:

detecting when said first output signal comprising consecutive positive pulses is present, or when said second output signal comprising consecutive negative pulses is present and providing said disable signal when either said first output signal or said second output signal is detected; and

inhibiting the passage of said received transmission when said disable signal is present.

23. A squelch circuit for receiving the transmission of data over a data transmission line and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble and providing an enable signal;

third sensing means connected to said first sensing means for detecting positive pulses of at least a predetermined positive threshold voltage level and continuing for a third predetermined duration, and providing a reset signal output to said indication means to prevent the generation of said enable signal; and

logic means for receiving said transmission and responsive to said enable signal for passing said transmission.

24. The squelch circuit of claim 23 further comprising fourth sensing means connected to said second sensing means for detecting negative pulses of at least a predetermined negative threshold voltage level and continuing for a fourth predetermined duration, and providing a reset signal output to said indication means to prevent the generation of said enable signal.

25. The squelch circuit of claim 24 wherein said indication means prevent the generation of said enable signal if said first output signal comprises consecutive positive pulses or if said second output signal comprises consecutive negative pulses.

26. A squelch circuit for receiving the transmission of data over a data transmission line and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble and providing an enable signal;

third sensing means connected to said second sensing means for detecting negative pulses of at least a predetermined negative threshold voltage level and continuing for a third predetermined duration, and providing a reset signal output to said indication means to prevent the generation of said enable signal; and

logic means for receiving said transmission and responsive to said enable signal for passing said transmission.

27. The squelch circuit of claim 26 wherein said indication means prevents the generation of said enable signal when said first output signal comprises consecutive positive pulses or when said second output signal comprises consecutive negative pulses.

28. A squelch circuit for receiving the transmission of data over a data transmission line and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble and providing an enable signal, said indication means preventing the generation of said enable signal when said first output signal comprises consecutive positive pulses or when said second output signal comprises consecutive negative pulses; and

logic means for receiving said transmission and responsive to said enable signal for passing said transmission.

29. A squelch circuit located at one node of a plurality of nodes in a data transmission network, for receiving the transmission of data over a data transmission line in said network and detecting a predetermined sequence of positive and negative pulses indicative of a preamble of a data stream, the circuit comprising:

first sensing means for receiving said transmission and detecting the presence of positive pulses of at least a predetermined positive threshold voltage level and continuing for at least a first predetermined duration, and providing a first output signal;

second sensing means for receiving said transmission and detecting the presence of negative pulses of at least a predetermined negative threshold voltage level and continuing for at least a second predetermined duration, and providing a second output signal;

means for generating a transmit signal indicative of the concurrent transmission by said one node and at least one other node of said network;

indication means responsive to said first and second output signals for detecting said predetermined sequence of positive and negative pulses indicative of said preamble, said indication means further responsive to said transmit signal for altering the duration of said predetermined sequence of positive and negative pulse and providing an enable signal; and

logic means for receiving said transmission and responsive to said enable signal for passing said transmission.

30. A method for distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting said noise, said data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said data transmission line;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for at least a first predetermined duration;

providing a first output signal when said positive pulses are detected;

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for at least a second predetermined duration;

providing a second output signal when said negative pulses are detected;

providing an enable signal when said first and second output signals are present in the same sequence as said predetermined sequence of positive and negative pulses indicative of the presence of said data stream preamble;

providing a disable signal when both said positive pulses of at least a predetermined positive threshold voltage level and said negative pulses of at least a predetermined negative threshold voltage level are absent for a third predetermined duration;

passing said received transmission when said enable signal is present; and

,

inhibiting the passage of said received transmission when said disable signal is present.

31. The method of claim 30 further providing the steps of:

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for a fourth predetermined duration, and providing a disable signal when said positive pulses continuing for a fourth duration are detected; and

,

inhibiting the passage of said received transmission when said disable signal is present.

34. A method for distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting said noise, said data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said data transmission line;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for at least a first predetermined duration;

providing a first output signal when said positive pulses are detected;

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for at least a second predetermined duration;

providing a second output signal when said negative pulses are detected;

providing an enable signal when said first and second output signals are present in the same sequence as said predetermined sequence of positive and negative pulses indicative of the presence of said data stream preamble;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for a third predetermined duration, and providing a disable signal when said positive pulses continuing for a third duration are detected;

passing said received transmission when enable signal is present; and

,

inhibiting the passage of said received transmission when said disable signal is present.

35. The method of claim 34 further comprising the steps of:

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for a fourth predetermined duration, and providing a disable signal when said negative pulses continuing for a fourth duration are detected; and

,

inhibiting the passage of said received transmission when said disable signal is present.

36. The method of claim 35 further comprising the steps of:

detecting when said first output signal comprising consecutive positive pulses is present, or when said second output signal comprising consecutive negative pulses is present and providing said disable signal when either said first output signal or said second output signal is detected; and

inhibiting the passage of said received transmission when said disable signal is present.

37. A method for distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting said noise, said data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said data transmission line;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for at least a first predetermined duration;

providing a first output signal when said positive pulses are detected;

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for at least a second predetermined duration;

providing a second output signal when said negative pulses are detected;

providing an enable signal when said first and second output signals are present in the same sequence as said predetermined sequence of positive and negative pulses indicative of the presence of said data stream preamble; and

,

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for a third predetermined duration, and providing a disable signal when said negative pulses continuing for a third duration are detected;

passing said received transmission when said enable signal is present; and

,

inhibiting the passage of said received transmission when said disable signal is present.

38. The method of claim 37 further comprising the steps of:

detecting when said first output signal comprising consecutive positive pulses is present, or when said second output signal comprising consecutive negative pulses is present and providing said disable signal when either said first output signal or said second output signal comprising consecutive pulses is detected; and

inhibiting the passage of said received transmission when said disable signal is present.

39. A method for distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting said noise, and data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said data transmission line;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for at least a first predetermined duration;

providing a first output signal when said positive pulses are detected;

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for at least a second predetermined duration;

providing a second output signal when said negative pulses are detected;

providing an enable signal when said first and second output signals are present in the same sequence as said predetermined sequence of positive and negative pulses indicative of the presence of said data stream preamble;

detecting when said first output signal comprising consecutive positive pulses is present, or said second output signal comprising consecutive negative pulses is present and providing a disable signal when either said first output signal or said second output signal comprising consecutive pulses is detected;

passing said received transmission when said enable signal is present; and

,

inhibiting the passage of said received transmission when said disable signal is present.

40. A method for distinguishing between a data stream and noise transmitted over a data transmission line in a network and for passing said data stream and inhibiting said noise, said data stream having a preamble with a predetermined sequence of positive and negative pulses, comprising the steps of:

receiving said transmission over said data transmission line;

generating a transmit signal when concurrent transmission is received over said data transmission line;

altering the duration of said predetermined sequence of positive and negative pulses when said transmit signal is present;

detecting when positive pulses of at least a predetermined positive threshold voltage level are present and continuing for at least a first predetermined duration;

providing a first output signal when said positive pulses are detected;

detecting when negative pulses of at least a predetermined negative threshold voltage level are present and continuing for at least a second predetermined duration;

providing a second output signal when said negative pulses are detected;

providing an enable signal when said first and second output signals are present in the same sequence as said predetermined sequence of positive and negative pulses indicative of the presence of said data stream preamble; and

passing said received transmission when said enable signal is present.