Automatic Gain Control Stress Measurement For Digital Carriers

• US 20090086804A1
• Filed: 09/30/2008
• Published: 04/02/2009
• Est. Priority Date: 10/01/2007
• Status: Active Grant

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Acterna LLC (Lumentum Holdings Inc.)
• Inventors: Chappell, Daniel K., Miller, Walter, Shi, Pingnan
• Granted Patent: US 8,184,684 B2
• Time in Patent Office: Days
• US Class Current: 375/228
• CPC Class Codes: H03G 3/3078 Circuits generating control signals for digitally modulated signals

Abstract

The testing equipment of the present invention calculates a single “AGC stress” value, which provides an indication of the stability of the level of a digital carrier based on the change in gain required to stabilize the power of an incoming cable signal over time. Ideally the AGC stress value is rated on a scale, e.g. 1 to 10 or 0 to 5, and is fed into the DQI measurement system as a new data model.

Claims

1. A method for determining the stability of a modulated carrier signal comprising:

a) receiving said modulated carrier signal in a device, including input circuitry with an automatic gain control system therein; and

b) measuring a degree to which said automatic gain control system is compensating for instability in said modulated carrier signal; and

c) providing a visual indication of the degree to which said automatic gain control system is compensating for instability in said modulated carrier signal.

2. The method according to claim 1, wherein step b) includes determining gain fluctuations required by the automatic gain control system.

3. The method according to claim 1, wherein step b) includes determining a change in the percentage of available gain from the automatic gain control system was utilized to compensate the modulated carrier signal from one time period to another time period.

4. The method according to claim 1, wherein step b) includes obtaining a minimum and a maximum value from an integrator register of the automatic gain control system for a predetermined number of samples over a predetermined update period;

and determining a stress index value based on the minimum and maximum values, which represents the degree to which said automatic gain control system is compensating for instability in said modulated carrier signal.

5. The method according to claim 4, further comprising comparing the index stress value to a threshold value, and providing a visual indication if the index stress value exceeded the threshold value.

6. The method according to claim 4, further comprising determining a relative value of the index stress value on a predetermined scale, which ranges from a first value corresponding to relatively no fluctuation to a second value corresponding to a threshold fluctuation value.

7. The method according to claim 4, wherein the update period is between 0.5 and 2 seconds.

8. The method according to claim 4, wherein the predetermined number of samples is greater than 100.

9. A testing device comprising:

an input port for receiving an input RF cable television signal channel;

a demodulator chip for demodulating the input RF cable television signal channel into a bit stream of data, the demodulator chip including an automatic gain control system comprised of a programmable gain amplifier and an automatic gain control loop for controlling the programmable gain amplifier;

a controller for determining a stress index value corresponding to a degree to which said automatic gain control system is compensating for instability in said cable television signal channel; and

a user interface for providing an indication of the stress index.

10. The testing device according to claim 9, wherein the controller is capable of determining gain fluctuations in the programmable gain amplifier required to compensate the input RF cable television signal channel over a predetermined time period, whereby the stress index value is based on the gain fluctuations.

11. The testing device according to claim 9, wherein the controller is capable of determining a change in the percentage of available gain from the programmable gain amplifier was utilized to compensate the input RF cable television signal channel from one time period to another time period, whereby the stress index value is based on the change in the percentage of available gain utilized.

12. The testing device according to claim 9, wherein the controller is capable of obtaining the minimum and maximum values from an integrator register of the programmable gain amplifier over a predetermined update period;

whereby the stress index value is based on the minimum and maximum values.

13. The testing device according to claim 9, wherein the controller is capable of comparing the stress index value to a threshold value, and providing a visual indication if the index value exceeded the threshold value.

14. The testing device according to claim 9, wherein the controller is capable determining a relative value of the index value on a predetermined scale, which ranges from a first value corresponding to relatively no fluctuation to a second value corresponding to a threshold fluctuation value.

15. The testing device according to claim 12, wherein the update period is between 0.5 and 2 seconds.

16. The testing device according to claim 12, wherein the predetermined number of samples is greater than 100.