Pulse or digital communications – Receivers – Automatic gain control
Reexamination Certificate
1998-02-05
2001-06-19
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Automatic gain control
C375S316000, C375S344000
Reexamination Certificate
active
06249554
ABSTRACT:
BACKGROUND OF THE INVENTION
The demodulation scheme described in application Ser. No. 09/114,948 (Farrow 31-29-3-7-2) provides for the receipt of quadrature amplitude modulated (QAM) analog signals. These analog signals are converted to digital representations by an analog-to-digital converter and demodulated to yield digital representations of in-phase and quadrature components of the analog QAM signal application Ser. No. 09/114,948 (Farrow 31-29-3-7-2) also describes the interpolation of the digital representations to create a sample stream having a frequency related to a desired baud rate. After decimation and filtering, these samples are provided, at the desired baud rate, to an equalizer. The samples provided to the equalizer are in the form of multibit samples, such as, for example, 10-bit samples.
It is preferable that the 10-bit samples provided to the equalizer cover most of the dynamic range of the equalizer. If some of the samples have a value outside the dynamic range of the equalizer, saturation will occur, resulting in a loss of information. Conversely, if the samples consistently have values less than the dynamic range of the equalizer, then the resolution is not optimized.
SUMMARY OF THE INVENTION
In a receiver, a digital automatic gain control circuit receives a series of digital samples representing at least one of an in-phase component and a quadrature component of a received signal, and provides scaled in-phase components and scaled quadrature components to an equalizer. The digital automatic gain control circuit includes a gain updating unit that receives a value representing at least one of an in-phase component and a quadrature component, receives a target reference value, and updates a gain value based on a difference therebetween. The digital automatic gain control circuit also includes a scalar that scales the received signal based on the updated gain value.
A method of controlling a gain of a stream of quadrature amplitude modulated digital values includes the steps of determining an average input power over a series of the digital values, comparing the average input power to a reference power to create a difference value, updating a gain value based on the difference value, and using the updated gain value to scale the stream of digital values.
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Mobin Mohammad Shafiul
Sufi Akkas T.
Agere Systems Guardian Corp.
Bayard Emmanuel
Pham Chi
Veschi John P.
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