Research And Design On A Wide Dynamic Range Of Open Loop Variable Gain Amplifier

Due to the impact of a variety of unpredictable disturbance factors exist in thenature of the air, so the strength of the receiver received external signal will be different.In order to improve the reception, general communications receiving system will havean AGC, and the VGA is a core part of the AGC. The next stage circuit of the VGA isADC. A variable gain amplifier is needed to meet the performance requirements of theADC. We can find that the performance of variable gain amplifiers has a great impacton the performance of the communication receiver system.Firstly, this paper analyzes the wireless receiver system ADC dynamic indicators,and VGA indicators for the relationship between the ADC and VGA, and thus gives theVGA indicators specific requirements. This paper introduces several commontraditional VGA’s structures. Especially for the open-ring structure VGA do a detaileddescription. This paper highlight introduces the gain dB linear control of open-loopstructure.Secondly, this paper starting from the ADC performance requirements of the radioreceiving system, VGA is designed to meet the excellent dynamic performance ADCrequires. In depth analysis the past VGA circuit structures and control characteristics,VGA built the exponential function control characteristics based on curve fitting. Thispaper is to design a60dB dynamic range variable gain amplifier, the operatingfrequency of the input signal from10MHz to70MHz. VGA using the open-loop sourcenegative feedback circuit structure. In order to make the gain of the VGA independenceenvironment, the current circuit of the constant transconductance provides currentsources to VGA, thus ensuring the stability of the gain value. High-pass filter connectedin series in VGA, not only to reduce the impact of low-frequency noise, more conduciveto the connection of the front and rear two stages VGAs.Finally, based on the3.3V0.13μm CMOS process simulation, the input signalfrequency is30MHz, and in order to make the output rail-to-rail input signal amplitudeis determined by gain value. The external effective voltage control range is0.5V to2.1V and bandwidth is71.94MHz to94.684MHz within the effective voltage control range. The minimum bandwidth is about1MHz due to the limitations of the high-passfilter. Total harmonic distortion is less than-63dB when the input signal frequency is30MHz. Noise figure is11.838dB to15.794dB. The noise spectral density is5.3312nV/sqrtHz at the maximum gain value. The noise spectral density is98.625nV/sqrtHz at the minimum gain value. The gain dynamic range is6.36dB to67.08dB. Gain value and voltage signal is approximately the dB linear relationship. Theaverage power consumption of VGA is27.77625mW.The simulation results show that the VGA designed in this paper can be used for12bit100MSPS ADC, and provide some reference to design wide dynamic range andhigh-speed high-precision VGA.