Design and Analysis of 28 GHz CMOS LNA and VGA Using Gain-Linearity-Boosting and Body Floating Techniques

We report the design and analysis of a 28 GHz CMOS low-noise amplifier (LNA) and variable-gain amplifier (VGA1) using coupled-transmission-line (CTL)-feedback technique, and another VGA (VGA2) without CTL-feedback for contrast. The CTL in conjunction with a coupling capacitance (<inline-formula> <tex-math notation="LaTeX">$C_{\text {ctl}}$ </tex-math></inline-formula>) contributes an in-phase gain at the output of the input stage. Over 21.9–29.1 GHz, 0.6–2.4 dB boosting in <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula> and 0.42–1.17 dB reduction in noise figure (NF) are achieved. The body-floating technique is used for NF reduction due to effective suppression of the substrate noise. An auxiliary-gain-linearity-enhancement (AGLE) stage is included in parallel with the output stage for gain and linearity boosting since it contributes an in-phase gain and exhibits better linearity [due to higher drain-source voltage (<inline-formula> <tex-math notation="LaTeX">$V_{\text {DS}}$ </tex-math></inline-formula>)]. For VGA1 and VGA2, an analog current-steering switch transistor <inline-formula> <tex-math notation="LaTeX">$M_{{5}}$ </tex-math></inline-formula> is in parallel with the output stage to tune its overdrive and <inline-formula> <tex-math notation="LaTeX">$V_{\text {DS}}$ </tex-math></inline-formula> for fine tuning of <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula>. Digital switch transistor <inline-formula> <tex-math notation="LaTeX">$M_{{6}}$ </tex-math></inline-formula> (in conjunction with the coupling capacitance <inline-formula> <tex-math notation="LaTeX">$C_{{3}}$ </tex-math></inline-formula> and resonant inductance <inline-formula> <tex-math notation="LaTeX">$L_{\text {res}}$ </tex-math></inline-formula>) is in parallel with the gain stage to control its ac <inline-formula> <tex-math notation="LaTeX">$V_{\text {DS}}$ </tex-math></inline-formula> for coarse tuning of <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula>. VGA1 adopts DTMOS-with-<inline-formula> <tex-math notation="LaTeX">$R_{B}$ </tex-math></inline-formula> switch for lower on-state (<inline-formula> <tex-math notation="LaTeX">$R_{\text {ch,on}}$ </tex-math></inline-formula>) and higher off-state channel resistance (<inline-formula> <tex-math notation="LaTeX">$R_{\text {ch,off}}$ </tex-math></inline-formula>). This leads to <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula> tuning range boosting. The LNA consumes 9.5 mW and achieves <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">$21.8~\pm ~1.5$ </tex-math></inline-formula> dB for 21.9–29.1 GHz (<inline-formula> <tex-math notation="LaTeX">$f_{\text {3dB}} =7.2$ </tex-math></inline-formula> GHz), minimum NF (NF<inline-formula> <tex-math notation="LaTeX">$_{\min }$ </tex-math></inline-formula>) of 1.98 dB, and average NF (NF<inline-formula> <tex-math notation="LaTeX">$_{\text {avg}}$ </tex-math></inline-formula>) of 2.32 dB, and figure-of-merit (FOM<inline-formula> <tex-math notation="LaTeX">$_{{2}}$ </tex-math></inline-formula>) of 74.1 nm<inline-formula> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>GHz<inline-formula> <tex-math notation="LaTeX">$^{\text {2/3}}$ </tex-math></inline-formula>/mW<inline-formula> <tex-math notation="LaTeX">$^{\text {1/3}}$ </tex-math></inline-formula>. VGA1 consumes 13.2 mW and achieves <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">$20.1~\pm ~1.5$ </tex-math></inline-formula> dB for 20.5–27.6 GHz (<inline-formula> <tex-math notation="LaTeX">$f_{\text {3dB}} =7.1$ </tex-math></inline-formula> GHz), <inline-formula> <tex-math notation="LaTeX">$S_{{21}}$ </tex-math></inline-formula> tuning range of 36.8 dB, NFmin of 1.74 dB, NFavg of 2.1 dB, and FOM2 of 66.5 nm<inline-formula> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>GHz<inline-formula> <tex-math notation="LaTeX">$^{\text {2/3}}$ </tex-math></inline-formula>/mW<inline-formula> <tex-math notation="LaTeX">$^{\text {1/3}}$ </tex-math></inline-formula>. The NFavg and FOM2 are one of the best results ever reported for LNAs and VGAs with <inline-formula> <tex-math notation="LaTeX">$f_{\text {3dB}}$ </tex-math></inline-formula> greater than 5 GHz and power dissipation lower than 15 mW.