Design Of Low Supply Voltage Variable Gain Amplifier

Low power consumption is a basic tendency of the wireless mobile terminal development and the research on decreasing dissipation of the variable gain amplifier,which is a key block of wireless radio frequency receiver,for example,the GPS receiver,has currently been becoming a popular issue.Decreasing the voltage of power,however,is the most effective method to reduce the power dissipation.The research and design on low voltage variable gain amplifier have a prime theory significance and application value.The thesis designed a low voltage variable gain amplifier,which can apply to GPS receiver.In order to acquire a proper dynamic gain range,the combination of coarse and fine gain structure was adopted.The coarse gain consisted of four fixed gain amplifiers,which can bias themselves in a direct coupling method.Whereas the fine gain stage employed an open loop of source degeneration structure,which was suitable in low voltage applications and at the time of simplifying circuit construction,the power consumption also reduced.After the simulation and verification of tape-out,the test results showed that the circuit worked steadily to achieve the original requirement,amplifying in an adjustable way and a high level,at 0.7V.The power consumption of the entire amplifier is 0.84mW and the maximum gain,at least,is above 76dB and the sensitivity of the receiver chain is-95dBm.Nevertheless,there was a common mode voltage shifting which was about 220mV and a saturated square wave with a low frequency at output nodes.After the analysis on the test result,the optimization and improvement were carried out and a low voltage variable gain amplifier circuit and layout,based on master-slave structure,were proposed.Certainly,the simulation was proceeded too.The common mode rejection brought from the tail current source of coarse gain stage improved and so did the voltage margin and output swing.At the time of achieving a high resolution of gain adjustment,the optimized circuit increased the stability of traditional close-loop structure and meanwhile,the gain unwarp phenomenon caused by the conventional source degeneration had been relieved.The results showed the optimized construction improved the reliability and stability.The common mode rejection of the coarse gain stage had increased by 48.6dB.The ability to restrain a small signal,in low frequency,is about-60dB and the variation amplitude of common mode voltage caused by process corner(TT/FF/SS)was ±1mV.The VGA had a dynamic gain range from 44.73dB to 81.6dB and its gain step is 5dB;gain step error is less than 0.5dB;-0.5dB bandwidth is 4.79MHz;noise figure is 28.6dB and the total power consumption is 1.2mW at 0.7V,which means that the primary demand achieved.