Design And Implementation Of Programmable Gain Amplifier (PGA) For IMT-A

In wireless communication systems, the transmission rate required is increasing; the modulation is more and more complex; longer and longer continuous communication time is required, and system sensitivity needs to be increased. All of these made the requirements of the variable gain amplifier's bandwidth, linearity, power consumption, noise and other performance indexes harder. Furthermore, with the using of deep sub-micron CMOS technology, the low voltage makes the design of VGA face many challenges in compromising between these performance indexes.In this paper, based on Cadence EDA platform, using TSMC 0.18μm process, a programmable gain amplifier for the IMT-A application is designed and implemented. For application in zero-IF architecture receiver, this paper designs and implements the DC offset cancellation circuit (DCOC). To reduce the power consumed, an AB-class output buffer is designed, making the maximum quiescent current of the whole circuit be 17mA. With the same main function of a general source follower, the AB-class output buffer consumes 7mA less current, and has smaller attenuation of the signal. The die area of the whole chip (including all PAD) is 800*700um2.According to testing, with 1.8V supply voltage, and the differential load impedance of 100Ω, the gain dynamic range of PGA is up to 63dB. Using a binary control, the gain step is 1dB, and the step error is within±0.38dB. Even with about 6dB attenuation of the buffer for test, the maximum gain of the overall circuit is 55dB, meanwhile the -3dB bandwidth is 92MHz. IIP3 in low gain mode is up to 17.5dBm, and the 1dB compression point up to 5.7dBm. According to simulation, with the high gain mode, at 10MHz the input referred noise (IRN) is about 6nV/Hz1/2.The programmable gain amplifier (PGA) designed and implemented in this paper is broadband, with large dynamic gain range and high linearity. It meets the design requirements of the application for IMT-A well, and lays a good foundation for the research of the other circuit blocks of IMT-A RF front-end.