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In this paper is discussed a class of Automatic Gain Control circuitry (AGC´s) for conditioning of complex modulated signals, considering the variation of the contour of the analog data frame (envelope) for a wide dynamic range. Some specific data media uses sensors (i.e. magnetic and optical) to read the signals with codified information, and require a special control loop regarding the signal frequency response. To do this control loop, the information used is the rate of change of the curve formed by the outline of analog data frame. Moreover, for complex modulating signals, as it is in some codified data media, the response is depending of the frequency and/or phase, thus requiring an adaptive loop´s control. This paper presents and discusses theoretical analysis and the experimental results using as test vehicle an adaptive AGC circuit having an input with 60dB of dynamic range. The circuitry was implemented in a process CMOS 0.35μm.

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