Programmable network tester with data formatter

• US 4,525,789 A
• Filed: 07/16/1982
• Issued: 06/25/1985
• Est. Priority Date: 07/16/1982
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Rubin, Harvey, Kemper, Kyran B.
• Primary Examiner(s): Krass, Errol A.
• Assistant Examiner(s): Teska, Kevin J.
• Application Number:
  US06/399,184
• Time in Patent Office: 1,075 Days
• Field of Search: 364/481, 364/550, 364/551, 364/571, 371/25, 371/26, 179/175.3 F, 179/175.3 R, 370/15, 324/73 AT, 324/73 R, 330/278
• US Class Current: 702/117
• CPC Class Codes: H04M 3/30 for subscriber's lines , for the local loop

Abstract

A mechanized system distributing the access, test and communication functions to the point of testing, typically the centralized switching facility serving the telephone loops and equipment to be tested. Computer (200) stores information about each subscriber loop in the geographical area served by a system. Front-end computers (220,221) interact with computer (200) to retrieve pertinent data regarding loops to be tested. Each switching facility in an area includes a loop testing system (e.g., 160) that implements the required functions. The communication functions residing in front-end computers (220,221) and loop testing systems (160,161) are coupled via a data communication network (140) in a manner that allows any front-end computer to communicate with any loop testing system. Users of the system control access and test from consoles having the capability of establishing independent communication paths over the national dial network for interactive tests on loops accessed through standard test trunks. Microprocessor-based circuitry is utilized for numerous system tasks such as signal generation, digital signal processing and controlling sensitive analog measurements. Signal generation includes digital generation of analog waveforms. Signal processing techniques incorporate various digital filters to analyze sample sequences derived from, for example, dial pulses and coin telephone signals. Sensitive analog measurements of loop characteristics are effected with a magnetic current detector that operates over broad current and frequency ranges. Frequency dependent measurements are converted to DC using synchronous demodulation techniques to enhance resolution.

Claims

1. A method for producing a digital word indicative of electrical characteristics of a circuit under test comprising the steps of applying a source signal to a port of said circuit and detecting a resultant signal produced at said port in response to said source, said method further comprising the steps of

generating a demodulating signal equal in frequency to said source signal,

frequency-shifting said resultant signal by demodulating said resultant signal with said demodulating signal and low-pass filtering to produce a baseband signal,

converting said baseband signal with analog-to-digital (A/D) means into a first encoded data sample represented by a plurality of bits,

determining the number of consecutive zeros in the most significant bit positions of said first encoded sample to obtain a gain factor,

amplifying said baseband signal in proportion to said gain factor to produce an amplified baseband signal,

converting said amplified signal into a second encoded data sample with said A/D means, and

forming said digital word by storing said second encoded sample in locations of said word.

2. A method for producing a digital word indicative of electrical characteristics of a circuit under test comprising the steps of

generating a source signal and a corresponding demodulating signal,

applying said source signal to a port of said circuit,

detecting a resultant signal produced at said port in response to said source signal,

multiplying said resultant signal by said demodulating signal to produce a received signal,

filtering said received signal with low-pass filter means to provide a baseband signal,

converting said baseband signal with high-speed analog-to-digital (A/D) means into a first encoded data sample represented by a plurality of bits,

determining the number of consecutive zeros in the most significant bit positions of said first encoded sample to obtain a gain factor,

amplifying said baseband signal in proportion to said gain factor to produce an amplified baseband signal,

converting said amplified baseband signal into a second encoded data sample with said A/D means, and

forming said digital word by storing said second encoded sample in locations of said word.

3. The method as recited in claim 2 wherein the step of forming said digital word by storing said second encoded sample in locations of said word further includes the steps of

filling a number of the least significant of said locations, in proportion to said gain factor, with zeros,

reversing the order of the bits of said second encoded sample and placing the reversed bits adjacent to said zeros, and

filling the remaining ones of said locations with bits representative of the polarity of said amplified baseband signal.

4. A method for producing first and second digital words indicative of electrical characteristics of a circuit under test, said method comprising the steps of

generating a source signal and corrsponding first and second demodulating signals,

applying said source signal to a port of said circuit,

detecting a resultant signal produced at said port in response to said source signal,

multiplying said resultant signal by said first demodulating signal to produce a first received signal,

filtering said first received signal with first low-pass filter means to provide a first baseband signal,

converting said first baseband signal with high-speed analog-to-digital (A/D) means into a first encoded data sample represented by a plurality of bits,

determining the number of consecutive zeros in the most significant bit positions of said first encoded sample to provide a first gain factor,

amplifying said first baseband signal in proportion to said first gain factor to produce a first amplified baseband signal,

converting said first amplified baseband signal into a second encoded data sample with said A/D means,

forming said first digital word by storing said second encoded sample in locations of said first word,

multiplying said resultant signal by said second demodulating signal to produce a second received signal,

filtering said second received signal with second low-pass filter means to provide a second baseband signal,

converting said second baseband signal with said A/D means into a third encoded data sample represented by a plurality of bits,

determining the number of consecutive zeros in the most significant bit positions of said third encoded sample to provide a second gain factor,

amplifying said second baseband signal in proportion to said second gain factor to produce a second amplified baseband signal,

converting said second amplified baseband signal into a fourth encoded data sample with said A/D means, and

forming said second digital word by storing said fourth encoded sample in locations of said second word.

6. The method as recited in claims 4 or 5 wherein the step of generating a source signal and corresponding first and second demodulating signals includes the step of supplying a cosinusoidal signal as said source signal and generating said first and second demodulating signals in in-phase and in quadrature relation, respectively, to said cosinusoidal signal.

5. A method for producing first and second digital words indicative of electrical characteristics of a circuit under test, said method comprising the steps of

generating a source signal and corresponding first and second demodulating signals,

applying said source signal to a port of said circuit,

detecting a resultant signal produced at said port in response to said source signal,

multiplying said resultant signal by said first and second demodulating signals to produce first and second received signals,

filtering said first and second received signals with first and second low-pass filter means, respectively, to produce first and second baseband signals,

converting said first baseband signal with high-speed analog-to-digital (A/D) means into a first encoded data sample represented by a plurality of bits,

determining the number of consecutive zeros in the most significant bit positions of said first encoded sample to provide a first gain factor,

amplifying said first baseband signal in proportion to said first gain factor to produce a first amplified baseband signal,

converting said first amplified baseband signal into a second encoded data sample with said A/D means,

forming said first digital word by storing said second encoded sample in locations of said first word,

converting said second baseband signal with said A/D means into a third encoded data sample represented by a plurality of bits,

determining the number of consecutive zeros in the most significant bit positions of said third encoded sample to provide a second gain factor,

amplifying said second baseband signal in proportion to said second gain factor to produce a second amplified baseband signal,

converting said second amplified baseband signal into a fourth encoded sample with said A/D means, and

forming said second digital word by storing said fourth encoded sample in locations of said second word by said second gain factor.

7. A method for producing a series of digital words for digital processing to determine electrical characteristics of a circuit under test, said method comprising the steps of

(i) generating a source signal and a corresponding demodulating signal,

(ii) applying said source signal to a port of said circuit,

(iii) detecting a resultant signal produced at said port in response to said source signal,

(iv) multiplying said resultant signal by said demodulating signal to produce a received signal,

(v) filtering said received signal with low-pass filter means to provide a baseband signal,

(vi) converting said baseband signal with high-speed analog-to-digital (A/D) means into a first encoded data sample represented by a plurality of bits,

(vii) determining the number of consecutive zeros in the most significant bit positions of said first encoded sample to obtain a gain factor,

(viii) amplifying said baseband signal in proportion to said gain factor to produce an amplified baseband signal,

(ix) converting said amplified baseband signal into a second encoded data sample with said A/D means,

(x) forming one word in said series of digital words by storing said second encoded sample in locations of said one word displaced by a number of positions corresponding to said number of consecutive zeroes, and

(xi) repeating steps (vi)-(xi) to generate said series of digital words.