Vol.32,No.7 Journal of Semiconductors July 2011 A wideband CMOS VGLNA based on single-to-differential stage and resistive attenuator for TV tuners* Han Kefeng(韩科锋)，Tan Xi(谈熙)t,Tang Zhangwen(唐长文)，and Min Hao(闵昊) State Key Laboratory of ASIC&System,Fudan University,Shanghai 201203,China Abstract:A wideband CMOS variable gain low noise amplifier(VGLNA)based on a single-to-differential(S2D) stage and resistive attenuator is presented for TV tuner applications.Detailed analysis of input matching,noise figure(NF)and linearity for S2D is given.A highly linear passive resistive attenuator is proposed to provide 6 dB attenuation and input matching for each gain stage.The chip was fabricated by a 0.18 um 1P6M CMOS process, and the measurements show that the VGLNA covers a gain range over 36.4 dB and achieves a maximum gain of 21.3 dB,a minimum NF of 3.0 dB,an IIP3 of 0.9 dBm and an IIP2 of 26.3 dBm at high gain mode with a power consumption less than 10 mA from a 1.8 V supply. Key words:S2D;VGLNA;TV tuner;attenuator;wideband;noise canceling D0:10.1088/1674-4926/32/7/075003 EEACC:1220 1.Introduction drawn a lot of attention recently.With the proposal of a noise canceling technique in wideband LNAs,S2D is predicted to The frequency plan of a DVB-T poses a great challenge to- be a wideband low noise amplifier owing to noise cancella- wards the design of a LNA over such a wideband of frequency tion4.S2D is also very linear because of distortion cancella- (50-860 MHz)because a traditional narrow band LNA can- tion[4.71.As a result,this topology is well studied and adopted not cover the full band and the frequency of 50 MHz is also in some wideband receivers[8].The well-known S2D(also a nightmare in realizing an on-chip LC tank.A tunable LNA called balun-LNA or active balun)is composed of a common suffers from the same problem.As a result,a wideband LNA gate (CG)stage with a common source(CS)stage,as shown shows its superiority over other solutions.With the technique in Fig.1. of noise canceling proposed in 20031,the NF can be lowered to 2 dB,thus it is more practical to implement a wideband low 2.1.Input impedance noise receiver,such as a TV tunerl2]or SDR receiver[31. Designing a LNA for a TV tuner pose three problems.The The impedance of the S2D seen from the input can be cal- first one is the wideband requirement,which is no more a prob- culated as lem with the scaling property of CMOS technology-the mea- sured 3 dB bandwidth of LNA can be up to several giga hertzl7. CG C1 However,flicker noise is a problem at 50 MHz for CMOS tech- Cgs1 +CG nology.The second is a linearity problem because the input sig- nal without filtering contains more than 100 channels allocated Here,CG is the capacitor(not shown here)connected to to the received band.so the 2nd and 3rd inter-modulation dis- M1 for AC grounding and gmi is the transconductance of CG. tortions are much more serious than for narrow band receivers Assuming CG>Cgsi and C1>Ces2,then Zin is given as (e.g.GSM)[5,121.The last one is that the input signal level can be up to 0 dBm when receiving all of the channels each with CG stage (A F)CS stage (A,.F) S2D=CG+CS (A.FSaD) a strong power,so an attenuation strategy is generally consid- ered(2.6,14] This paper presents a highly linear,low-noise wideband VGLNA based on a S2D and resistive attenuator for TV tuner applications9.A new insight into noise in S2D is given.An attenuator employing an RF switch with fewer parasitics and M2 better linearity is presented. 2.Single-to-differential stage The S2D stage with a history of over 20 years[iol has Fig.1.CG and CS stages form a noise canceling S2D stage. Project supported by the National Science Funding of China(No.60876019),the National S&T Major Project of China(No.2009ZX0131- 002-003-02),the Shanghai Rising-Star Program,China (No.09QA1400300),the National Scientists and Engineers Service for Enterprise Program,China (No.2009GJC00046),and the ASIC State-Key Laboratory Funding.China (No.09MS007). Corresponding author.Email:tanxi@fudan.edu.cn Received 19 December 2010,revised manuscript received 2 March 2011 C2011 Chinese Institute of Electronics 075003-1Vol. 32, No. 7 Journal of Semiconductors July 2011 A wideband CMOS VGLNA based on single-to-differential stage and resistive attenuator for TV tuners Han Kefeng(韩科锋), Tan Xi(谈熙) Ž , Tang Zhangwen(唐长文), and Min Hao(闵昊) State Key Laboratory of ASIC & System, Fudan University, Shanghai 201203, China Abstract: A wideband CMOS variable gain low noise amplifier (VGLNA) based on a single-to-differential (S2D) stage and resistive attenuator is presented for TV tuner applications. Detailed analysis of input matching, noise figure (NF) and linearity for S2D is given. A highly linear passive resistive attenuator is proposed to provide 6 dB attenuation and input matching for each gain stage. The chip was fabricated by a 0.18 m 1P6M CMOS process, and the measurements show that the VGLNA covers a gain range over 36.4 dB and achieves a maximum gain of 21.3 dB, a minimum NF of 3.0 dB, an IIP3 of 0.9 dBm and an IIP2 of 26.3 dBm at high gain mode with a power consumption less than 10 mA from a 1.8 V supply. Key words: S2D; VGLNA; TV tuner; attenuator; wideband; noise canceling DOI: 10.1088/1674-4926/32/7/075003 EEACC: 1220 1. Introduction The frequency plan of a DVB-T poses a great challenge to￾wards the design of a LNA over such a wideband of frequency (50–860 MHz) because a traditional narrow band LNA can￾not cover the full band and the frequency of 50 MHz is also a nightmare in realizing an on-chip LC tank. A tunable LNA suffers from the same problem. As a result, a wideband LNA shows its superiority over other solutions. With the technique of noise canceling proposed in 2003Œ1, the NF can be lowered to 2 dB, thus it is more practical to implement a wideband low noise receiver, such as a TV tunerŒ2 or SDR receiverŒ3 . Designing a LNA for a TV tuner pose three problems. The first one is the wideband requirement, which is no more a prob￾lem with the scaling property of CMOS technology — the mea￾sured 3 dB bandwidth of LNA can be up to several giga hertzŒ7 . However, flicker noise is a problem at 50 MHz for CMOS tech￾nology. The second is a linearity problem because the input sig￾nal without filtering contains more than 100 channels allocated to the received band, so the 2nd and 3rd inter-modulation dis￾tortions are much more serious than for narrow band receivers (e.g. GSM)Œ5; 12. The last one is that the input signal level can be up to 0 dBm when receiving all of the channels each with a strong power, so an attenuation strategy is generally consid￾eredŒ2; 6; 14 . This paper presents a highly linear, low-noise wideband VGLNA based on a S2D and resistive attenuator for TV tuner applicationsŒ9. A new insight into noise in S2D is given. An attenuator employing an RF switch with fewer parasitics and better linearity is presented. 2. Single-to-differential stage The S2D stage with a history of over 20 yearsŒ10 has drawn a lot of attention recently. With the proposal of a noise canceling technique in wideband LNAs, S2D is predicted to be a wideband low noise amplifier owing to noise cancella￾tionŒ4. S2D is also very linear because of distortion cancella￾tionŒ4; 7. As a result, this topology is well studied and adopted in some wideband receiversŒ8. The well-known S2D (also called balun-LNA or active balun) is composed of a common gate (CG) stage with a common source (CS) stage, as shown in Fig. 1. 2.1. Input impedance The impedance of the S2D seen from the input can be cal￾culated as Zin D  CG Cgs1 C CG ￾ gm1 C sCgs1
C C1 Cgs2 C C1 sCgs2￾1 : (1) Here, CG is the capacitor (not shown here) connected to M1 for AC grounding and gm1 is the transconductance of CG. Assuming CG  Cgs1 and C1  Cgs2, then Zin is given as Fig. 1. CG and CS stages form a noise canceling S2D stage. * Project supported by the National Science Funding of China (No. 60876019), the National S&T Major Project of China (No. 2009ZX0131- 002-003-02), the Shanghai Rising-Star Program, China (No. 09QA1400300), the National Scientists and Engineers Service for Enterprise Program, China (No. 2009GJC00046), and the ASIC State-Key Laboratory Funding, China (No. 09MS007). Ž Corresponding author. Email: tanxi@fudan.edu.cn Received 19 December 2010, revised manuscript received 2 March 2011 c 2011 Chinese Institute of Electronics 075003-1