A Low Noise Variable Gain Amplifier With Low Phase Error for X- and Ku-Band Phased Arrays

In this article, we present a detailed analysis of current steering, wideband, low noise, variable gain amplifier (VGA) and a novel method to decrease its phase and amplitude errors. A low noise VGA (LNVGA) has been designed using this innovative method in IHP's 0.13 $\mu$ m SiGe BiCMOS technology. In this proposed method, a high impedance seen from the base of the current steering transistor replaces a low impedance to reduce the loading of the current steering device and phase variations, eventually. The operating frequency spans from 8 to 18 GHz. The measurements indicate that the maximum gain is 12.4 dB, and the minimum noise figure (NF) is 1.93 dB at the reference state. The minimum measured root-mean-square (rms) phase and amplitude errors are 0.8 $^{\circ}$ and 0.04 dB, respectively, for a 0.5 dB step size and 16 dB attenuation range. The attenuation range can be increased by up to 30 dB, albeit at the cost of accruing additional phase and amplitude errors. The dc power consumption of the design is 24 mW, and the maximum input 1-dB compression point is 3.9 dBm. The overall dimensions of the chip is 0.58 mm $^2$ including pads.