Publication: Design of variable amplifier for phone ic
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Date
2008-05-01
Authors
Lai, Yoong Yoong
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Abstract
In this project, it will involve designing a speech circuit for the phone IC. The objective of this speech circuit is to have a variable amplifier to control the audio level of the human voice. Simply said, the objective of this project is to come out with a variable and high gain multistage amplifier. Other specifications such as the gain bandwidth, phase margin, common mode input range and maximum output range will be considered in the design. The project will first start with the design of a single open loop amplifier with a gain of around 60dB. Then it will be used as a closed loop amplifier with a gain of 20dB. The reason for using a closed loop amplifier compare to open loop amplifier is to achieve a much more stable amplifier. These closed loop amplifier will then be cascaded in 3 stages to provide a gain of 60dB. Lastly, a gain control circuit is added to the multistage amplifier to control and vary the gain. Throughout the project, the open loop gain obtained from the single amplifier is 53.05dB. Besides, the closed loop gain resulted from the inverting amplifier and non-inverting amplifier obtained is 19.75dB and 19.78dB each. The maximum gain obtained for the design of the variable amplifier altogether is 58.93dB.