A Low Distortion and Low Noise Differential Amplifier Suitable for 3G LTE Applications Using the Even- and Odd-Mode Impedance Differences of a Bias Circuit

Toshifumi NAKATANI  Koichi OGAWA  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.6   pp.844-853
Publication Date: 2008/06/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.6.844
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuits and Related SoC Integration Technologies)
Category: 
Keyword: 
3rd order intermodulation,  noise figure,  differential amplifier,  2-tone difference frequency,  even- and odd-mode impedance difference,  input bias circuit,  3rd generation long term evolution,  

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Summary: 
A low distortion and low noise differential amplifier using the difference between the even- and odd-mode impedances is proposed. In order to realize an amplifier with high OIP3 and low NF characteristics, the impedance of the bias circuit should be low (<300 Ω) at the difference frequency and high (>4 kΩ) at the carrier frequency. Although the frequency response of the bias circuit impedance can only meet these conditions with difficulty, owing to the 20 MHz Tx signal bandwidth for 3G LTE, the proposed amplifier can achieve the impedance difference using the properties of a differential configuration where the difference frequency signal is the even-mode and the carrier frequency is the odd-mode. It has been demonstrated that the NF of the proposed amplifier, which has been fabricated in 0.18 µm SiGe BiCMOS technology operating at 2.14 GHz, can be kept to 1.6 dB or less and an OIP3 of 9.0 dBm can be achieved, which is 3 dB higher than that of a conventional amplifier, in the condition where the power gain is greater than 18 dB.