| 摘要 |
A variable gain amplifier having a decibel(dB) linear characteristic is provided to implement a cubic polynomial approximated to an exponential function through a CMOS element by representing the cubic polynomial as an inverse proportional term, a second term, and a constant term. A variable gain amplifier(40) having a decibel linear characteristic includes the steps of: approximating a variable gain which is represented as an exponential function of a control voltage to a ratio of a denominator and a nominator of a cubic polynomial of a control voltage, and generating a denominator current and a nominator current corresponding to the denominator and the denominator; and amplifying an input voltage to a voltage gain represented as a ratio of the denominator current and the nominator current, and generating a dB linear output voltage for the input voltage. The step of generating the denominator current and the nominator current includes the step of converting the cubic polynomial of the denominator and the nominator to have an inverse first term, a second term, and a first term of the control voltage, and generating currents corresponding to each converted term.
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