High Gain and Balanced Output Balun–LNA Employing Positive Feedback Technique for Tuner of Digital Televisions

High gain Balun-low-noise-amplifier (LNA) is proposed for tuner of digital televisions (DTVs). The proposed Balun-LNA is based on CS-CG (common-source-common-gate) structure. To improve the isolasion and frequency response, Balun-LNA has cascode transistors before load resistors. Balun-LNA uses current-bleeding circuit to increasie transconductance of CS transistor, so that current-bleeding transistor has transconductance of N-۱ times larger than transconductance of cascode transistor. Thereby, transconductance and current of CS transistor are increased N times, as N-۱ times of current pass to current-bleeding transistor. Therefore current of CG and CS stages stay identical. Also, Balun-LNA employs a positive feedback to satisfy input impedance matching and CG transistor has higher transconductance. By increasing transconductance of CS and CG transistors, the proposed Balun-LNA achieves to high voltage gain. Accordingly, CG and CS tansistors have symmetrical currents and loads at the differential output of the proposed Balun-LNA. Symmetrical loads cause the balanced differential outputs. This proposed Balun-LNA is designed in ۹۰-nm CMOS technology and covers the frequency range of ۴۰ MHz to ۱GHz. This Balun-LNA achieves the voltage gain of ۲۲.۶ dB, S۱۱ of less than -۱۰ dB and the Minimum NF of ۵ dB. This Balun-LNA operates at the nominal supply voltage of ۲.۲v.

Keywords:

Balun-LNA , High Gain , Noise Cancelling , Positive Feedback , Symmetrical Loads , Tuner of Digital Televisions