A differential automatic gain control （AGC） circuit is presented. The AGC architecture contains twostage variable gain amplifiers （VGAs） which are implemented with a Gilbert cell, a peak detector （PD）, a low pass filter, an operational amplifier, and two voltage to current （V-I） convertors. One stage VGA achieves 30 dB gain due to the use of active load. The AGC circuit is implemented in UMC 0.18-um single-poly six-metal CMOS process technology. Measurement results show that the final differential output swing of the 2nd stage VGA is about 0.9-Vpp; the total gain of the two VGAs can be varied linearly from -10 to 50 dB when the control voltage varies from 0.3 to 0.9 V. The final circuit （containing output buffers and a band-gap reference） consumes 37 mA from single 1.8 V voltage supply. For a 50 mV amplitude 60% modulation depth input AM signal it needs 100 us to stabilize the output. The frequency response of the circuit has almost a constant -3 dB bandwidth of 2.2 MHz. Its OIP3 result is at 19 dBm.
提出了一种应用于超高频(Ultra high frequency,UHF)射频识别(Radio frequency identification,RFID)标签芯片的射频测试技术。针对UHF RFID标签芯片射频电路的特殊工作方式,该技术可对芯片的输入阻抗和灵敏度进行准确测量,并同时完成芯片功能验证。与传统的RFID标签芯片射频测试技术相比,文中的方案利用商用阅读器和可调衰减器代替了高端或RFID专用测试设备,因此极大降低了测试成本。利用该测试方案,对已开发的UHF RFID标签芯片进行了测试与验证,并利用测试结果完成了折叠偶极子天线设计以实现芯片与天线之间的阻抗匹配。将芯片与天线组装成无源标签,其灵敏度可达-10.5 dBm。实验结果证明了该方案的正确性。
