Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Logarithmic
Reexamination Certificate
2000-03-23
2001-05-08
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Logarithmic
C327S359000
Reexamination Certificate
active
06229374
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of variable gain amplifiers.
2. Prior Art
Amplifiers having a gain control capability are commonly used in wireless cell phone and other analog circuit applications. In the cell phone case, a signal is received on an antenna, with the strength of the received signal varying to a very large degree as the cell phone moves with respect to the base station (transmitted signal). A simple fixed gain receiver would amplify the variation to provide a widely varying signal to the analog-to-digital conversion circuitry within the cell phone that converts the signal to a digital signal for further processing. Such a wide variation in signal strength would result in an unacceptable error when converted to digital form by the analog-to-digital converter circuitry.
To avoid these problems, a variable gain amplifier is used to adjust the gain in the path of the received signal so that the full available range of the analog-to-digital converter circuitry may be used. In such applications, it is desired to provide a variable gain receive path amplification that produces a logarithmic characteristic in the gain path with a gain control signal such that the decibels of gain is linearly related to the gain control signal VAGC controlling the amplifier stage(s).
BRIEF SUMMARY OF THE INVENTION
Variable gain amplifiers and methods having a logarithmic gain control function are disclosed. The variable gain amplifiers have a first inverse hyperbolic tangent stage having a current input responsive to a gain control signal, a second inverse hyperbolic tangent stage responsive to the output of the first hyperbolic tangent stage, and a Gilbert cell providing an amplifier output responsive to an amplifier input with a gain responsive to the output of the second inverse hyperbolic stage. The inverse hyperbolic gain response is altered to closely approximate the desired logarithmic characteristic by including a circuit responsive to the gain control signal to provide a current input to the first inverse hyperbolic stage which is nonlinear with respect to the gain control signal.
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Blakely , Sokoloff, Taylor & Zafman LLP
International Business Machines - Corporation
Tran Toan
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