Comparative investigation between a single ended and a balanced IF VGA

Variable gain IF amplifier (VGA) based on single ended and Gilbert Cell topology have been designed and characterized. A comparative investigation has been carried out between the two topologies. The source feedback topology has been used for the single ended VGA and for the Gilbert Cell VGA, the gain is controlled by steering the drain current. Overall dynamic gain variation range is 13 dB with a maximum gain of 13 dB for the single ended VGA whereas for the Gilbert cell VGA, it is 16 dB and 10 dB, respectively. The -3 dB bandwidth is 4 GHz and the maximum value of 1 dB output compression is -6.2 dBm for the single ended VGA. The measured IP3 is 8.2 dBm referred to the output. DC power consumption is 75 mW. For the Gilbert Cell VGA, the -3 dB bandwidth is 2.25 GHz and maximum dissipated DC power is 100 mW. Maximum value of 1 dB compression point and IP3, both referred to the output, are 2 dBm and 9.87 dBm, respectively. Both the circuits were implemented on 0.15mum GaAs pHEMT technology. The active circuit area of Gilbert Cell VGA is 1.7 mm times 1.6 mm and the single ended VGA is 1.3 mm times 1.3 mm