Abstract
This paper presents the analysis and design of the harmonic rejection (HR) low-noise amplifier (LNA) with the fully passive source degeneration notch filter. The proposed HR LNA provides the rejection for the strong harmonics ( 3 r d ) of the local oscillator (LO) frequencies, where the HR mixer does not provide sufficient HR performance. The proposed 3 r d harmonic notch filter modulates the source degeneration factor and the impedance matching performance thereafter. This effect further helps the blocking of the harmonic signal. The proposed LNA provides 11 dB gain at the fundamental frequency (2.1 GHz) while rejecting the 3rd harmonic component by 37 dBc. Compared to the conventional LNA, the 3rd harmonic notch performance is improved by 23 dB. Additionally, the LNA achieves a minimum noise figure of 3.1 dB, third order input intercept point ( I I P 3 ) of 0.5 dBm, input reflection (S 11 ) below −10 dB from 1.8 GHz–2.3 GHz operational frequency range, and consumed 19 mW of power from a 1.2 V supply.
Highlights
The switching mixer down-converts the harmonics of the local oscillator (LO) signal and corrupts the desired signal in RF receivers
A frequency translation can be achieved by breaking the linear time-invariant (LTI) property and the linear time-varying switching mixer is the norm for modern RF receivers due to its superior performance in terms of the conversion gain and noise figure [1,2,3]
The novelty of the proposed HR low-noise amplifier (LNA) is due to features which include: (1) the harmonic filtering occurs before the current to voltage conversion in the load of the LNA and the desensitization due to the strong blockers is prevented in the first stage of the receiver chain; (2) the harmonic rejection requirement on the HR mixer is significantly relaxed with the help of HR LNA; (3) the proposed source degeneration notch filter is fully passive and incurs no additional current consumption, and; (4) the source degeneration factor is modulated for the rejection of 3rd harmonic and the blockers around 3ωo of the LNA is reflected across the antenna-LNA interface
Summary
The switching mixer down-converts the harmonics of the local oscillator (LO) signal and corrupts the desired signal in RF receivers. The switching mixer, on the other hand, is notorious for harmonic spurious issue, where the square-wave-like local oscillator LO signal down-converts the interferences at the harmonics of the LO fundamental frequency (ωo ) [4]. This harmonic alias is a serious problem for broadband radio, where the larger blockers are passed upon the receiver without any pre-filtering (attenuation) and harmonic rejection (HR) mixer has to be used, albeit with a circuit complexity and an in-sufficient HR performance [5,6]. The novelty of the proposed HR LNA is due to features which include: (1) the harmonic filtering occurs before the current to voltage conversion in the load of the LNA and the desensitization due to the strong blockers is prevented in the first stage of the receiver chain; (2) the harmonic rejection requirement on the HR mixer is significantly relaxed with the help of HR LNA; (3) the proposed source degeneration notch filter is fully passive and incurs no additional current consumption, and; (4) the source degeneration factor is modulated for the rejection of 3rd harmonic and the blockers around 3ωo of the LNA is reflected across the antenna-LNA interface
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