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Recently, few topologies implementing noise cancellation techniques have been re-
ported. The thermal noise cancellation technique which uses resistive feed forward CS
configuration was implemented for an LNA operating below 2 GHz [6]. However, this
technique was extended to higher frequencies by using inductive peaking which shows
reduction in noise figure in 3.1-10.6 GHz frequency range [7]. In addition, various
other noise cancellation techniques has been reported in literature such as simultaneous
noise and third order distortion cancellation technique in CG-CS cascade LNA operat-
ing till 2.1 GHz [8] and resistive feed forward noise cancellation technique in two stage
differential transconductance LNA operating till 4.5 GHz [9]. Hence it is evident that
noise cancellation techniques usually do not consider much about gain improvement.
In this work, we propose a noise cancellation technique which not only reduces the
noise but also improves the gain and is novel to best of our knowledge. In order to
cancel the dominant noise, we analyzed the noise contributions from both active and
passive components in CG UWB LNA reported in ref. [10]. The input matching device
viz. first CG transistor was identified as the most dominant noise source. The technique
is based on combining two paths one with reversed phase noise signal and the other
with non-reversed phase noise signal, simultaneously the RF signals in the two paths
will be in phase. The two parallel paths were designed by symmetrical cascade combi-
nation of CG-CS and CS-CG stages. Theoretical model of noise cancellation is pre-
sented along with the derived equation of overall noise figure and implementation is
done using TSMC 0.18 µ m CMOSRF technology on Cadence Spectre RF tool.
2
Noise Analysis
A three stage UWB LNA as shown in Fig. 1 is taken for detailed analysis of noise
sources [10]. First stage is a CG stage followed by cascode CS stage and resistive
feed forward cascode CS stage with a buffer at the output. Major noise contribution of
this UWB LNA is from the CG transistor (M1) which is approximately 42% over the
entire range of 3.1-10.6 GHz shown in Fig. 2, extracted from noise simulation results.
Second stage CS transistor (M2) contributes 22% for the entire range and its noise
contribution is more near the corner frequencies. This is due to the restriction of nar-
row band characteristics of CS amplifier while CG amplifier shows WB characteris-
tics and its noise contribution is almost equal (2.8 ± 0.3) dB for the entire range of
UWB as shown in Fig. 3. Third stage noise contribution is negligible as it receives
the amplified signal from the earlier two stages. Therefore, it is desirable to suppress
the noise contribution of M1.
Fig. 1.
UWB LNA without noise cancellation
