Research Of Wide Swing CMOS Programmable Gain Amplifier

For the CCD image processing system, the variable gain amplifier(VGA) is an important component in the analog front end(AFE) circuit. CMOS-based VGA can be used to set different gain values in different environments, adjust the input signal dynamic range and stabilize output signal power, providing a constant output swing signal to analog-to-digital converter(ADC). VGA lies in the front-end of CCD systems and deals with a wide swing input signal, so wide swing and high linearity are the important design specifications of the thesis. Additionally, AGC system requires a dB-linear gain VGA, so a wide range gain variation range is another important indicator of this thesis.For CCD application, this work proposed a wide swing CMOS programmable gain amplifier, which can be configured to amplify 0-2V discrete signal or continuous signal to 2V full swing resulting in 15 bit ENOB for the ADC stage. The PGA is mainly composed of four parts: a voltage clamp circuit, a source follower circuit, an R-2R attenuation network and a fixed gain amplifier. The design difficulty mainly focuses on the stability of the high performance gain amplifier with three-stage. We introduces two compensation methods of common source cascade compensation and current mirror compensation to compensate the op-amp.The PGA is fabricated in SMIC 0.18?m 1P6 M CMOS technology, and shows a 42 dB range with linearity error of less than ±0.4dB with the supply voltage of 3V. The range of gain variation can be controlled from-1.08 to 41.06 dB, the step of the gain is 6.02 dB, and the-3dB bandwidth is 114.58 MHz.For AGC loop, VGA needs to be dB-linear gain control characteristics. This work proposed an open-loop VGA, which is characterized by a wide range gain variation. The VGA is mainly composed of three parts: the control circuit, the variable gain circuit and the common-mode feedback circuit. The control circuit is constructed by a new approximated exponential function, which can provide a wide dB-linear variation. The variable gain circuit is adopted by the variation of trans-conductance and loads. The VGA is fabricated in SMIC 0.18?m 1P6 M CMOS technology and shows a 62-dB linear range with linearity error of less than ±3dB with the supply voltage of 3V. The range of gain variation can be controlled from-30 to 32 dB.The input IP1 dB varies from-20.79 to 8.72 dBm and the-3dB bandwidth is from 269.6MHz(at maximum gain of 32 dB) to 2.609GHz(at minimum gain of-30 dB).