王春华-湖大信息科学与工程学院.pdf

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS Int. J. Circ. Theor. Appl. 2015; 43:1794–1800 Published online 10 October 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cta.2028 LETTER Design and simulation of novel ampliﬁer-based mixer for ISM band wireless applications Jie Jin1,2, Chunhua Wang1,*†, Jingru Sun1 and Sichun Du1 1 College of Computer Science and Electronic Engineering, Hunan University, Changsha 410082, PR China 2 College of Information Science and Engineering, Jishou University, Jishou 416000, PR China SUMMARY This letter describes a low-voltage low-power (LV-LP) 2.4-GHz mixer for Industrial, Scientiﬁc and Medical (ISM) band wireless applications. The approach is based on a two-stage ampliﬁer, and the Gilbert switch stage is inserted between the two ampliﬁer stages. The proposed ampliﬁer-based mixer delivers a remarkable conversion gain of 13 dB with a local oscillator (LO) power of 7 dBm, while consuming only 1.05-mW DC power from a 0.8-V supply voltage. The input-referred third-order intercept point (IIP3) of the mixer is 3.82 dBm, and the chip area is only 0.429 mm2. The results indicate that this mixer is suitable for the low-voltage low-power applications. Copyright © 2014 John Wiley & Sons, Ltd. Received 16 December 2013; Revised 3 August 2014; Accepted 1 September 2014 KEY WORDS: CMOS; low voltage low power; ampliﬁer; mixer 1. INTRODUCTION Due to the limitations of battery capacity, the low-voltage low-power and highly integrated circuits are required in the radio frequency (RF) wireless communication systems, such as the IEEE 802.11b WLAN and the Bluetooth technologies working at 2.4-GHz industrial, scientiﬁc and medical (ISM) band. Mixer is one of the most important analog blocks in the wireless communication system. Typically, the Gilbert active mixers [1–10] are widely used in the wireless communication systems for their superior conversion gain and port to port isolation. However, conventional Gilbert active mixers generally consume a signiﬁcant portion of the power of the transceiver, and the LV–LP mixers have received considerable attentions in recent years. Several techniques have been reported to decrease the supply voltage and the power consumption of the mixers, such as folded technique [11–14] and current reuse technique [15, 16]. In the folded technique, the RF stage is separated from the LO stage, which reduces the number of stacked transistors, and the supply voltage is decreased. However, because of the increased branch currents of the RF stage, the total power consumption does not reduce signiﬁcantly. In the current reuse technique, the dissipated current in any stage is reused in other stages, but the stacked transistors are not reduced, and the supply voltage is not decreased. In this work, an ampliﬁer-based mixer is presented. The ampliﬁer consists of a resistor feedback stage and a common source stage with LC loads. The number of stacked transistors of the ampliﬁer is only one, which makes the supply voltage relatively low. The Gilbert switches are inserted between the two ampliﬁer stages, and the Gilbert switches are turned on and off by the LO signals. *Correspondence to: Chunhua Wang, College of Computer Science and Electronic Engineering, Hunan University, Changsha 410082, PR China. † E-mail: 124900808@qq.com Copyright © 2014 John Wiley & Sons, Ltd. CMOS, LOW-VOLTAGE LOW-POWER, AMPLIFIER, MIXER 1795 The second stage of the ampliﬁer works only when the Gilbert switches are opened by the LO signals, which further reduces the power consumption of the mixer. There are three fundamental issues discussed in this letter: First, novel ampliﬁer-based mixer architecture is presented; second, because the novel mixer is realized based on a two-stage ampliﬁer, and the conversion gain of the mixer is relatively large; the last, the number of stacked transistors of the mixer is one, and the supply voltage is reduced to 0.8 V. Moreover, the turning on and off the second section of the ampliﬁer is controlled by the Gilbert switches, which reduces the power consumption of the mixer. The Cadence IC Design Tools 5.1.41 post-layout simulation results are included to conﬁrm all the theory. 2. CIRCUIT DESCRIPTION 2.1. The conventional gilbert cell mixer Figure 1 is the circuit schematic of conventional Gilbert mixer. The Gilbert mixer has the advantages of low even order distortion and good port to port isolation. However, there are three stacked transistors in the Gilbert mixer, and the supply voltage is relatively high. Moreover, all the transistors in the Gilbert mixer operate in the saturation region, and the power consumption is high. The conversion gain of the conventional Gilbert cell mixer is [17]: 2 AV ¼ gm1 RL π (1) 2.2. The two-stage ampliﬁer Figure 2 is the two-stage ampliﬁer with the Gilbert switch. This ampliﬁer consists of a resistor feedback stage and a common source stage with LC load. M1, R1 and Rf constitute the ﬁrst resistor feedback stage. A routine circuit analysis reveals that the voltage gain of the ﬁrst stage is: AV 1 ≈ gm1 • R1 ==Rf (2) where gm1 is the transconductance of the transistor M1. Figure 1. Circuit schematic of the conventional Gilbert cell mixer. Copyright © 2014 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. 2015; 43:1794–1800 DOI: 10.1002/cta 1796 J. JIN ET AL. Figure 2. The two-stage ampliﬁer with the Gilbert switch. M7, L3 and C3 constitute the second common source stage. Similarly, the voltage gain of the second stage is: 1 (3) AV2 ¼ gm7 • ro7 == jωL1 þ jωC3 where gm7 is the transconductance of the transistor M7, and ro7 is the output resistance of M7. The paralleled resonant load (L1 and C3) is chosen to be resonated at 2.4 GHz, and the voltage gain of the second stage at 2.4 GHz could be expressed as: AV2 ≈ gm7 ro7 (4) From equations (2) and (4), it is clear that, the voltage gain of the two-stage ampliﬁer could be expressed as: AV ¼ AV1 •AV2 ≈gm1 gm7 • R1 ==Rf •r o7 (5) The Gilbert switch is inserted between the two ampliﬁer stages. When the switch is turned off, the working conditions of the transistor M7 are not satisﬁed, and the second stage of the ampliﬁer will not work. When the switch is turned on, M7 will operate in the saturation region. In other words, the second stage of the ampliﬁer only works when the switch is turned on, which reduces the power consumption of the ampliﬁer. 2.3. The proposed ampliﬁer-based mixer The proposed ampliﬁer-based mixer is presented in Figure 3. From Figure 3, it is clear that, the number of stacked transistors of the ampliﬁer-based mixer is only one, which makes the supply voltage relatively low. M1, M2, R1, R2 and Rf constitute the ﬁrst ampliﬁer stage of the mixer. M3–M6 are the Gilbert switches, and the turning on and off the switches is controlled by the LO signals. Figure 4 is the relationship between the switches and the LO signals. In Figure 4, t0 to t5 is a period of the LO signal, From t1 to t2, and t3 to t4, (vLO+ + Vbs) > Vth or (vLO- + Vbs) > Vth, the transistors M3 and M6 or M4 and M5 are opened, the transistors M6 and M7 work in the saturation region and the whole mixer works properly. From t0 to t1, t2 to t3 and t4 to t5, when the Gilbert switches are closed, and the transistors M6 and M7 stop working, which could reduce the power consumption of the mixer. Copyright © 2014 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. 2015; 43:1794–1800 DOI: 10.1002/cta CMOS, LOW-VOLTAGE LOW-POWER, AMPLIFIER, MIXER 1797 Figure 3. The proposed ampliﬁer-based mixer. Figure 4. The relations between the switches and the LO signals. M7, M8, L1, L2, C3 and C4 constitute the second ampliﬁer stage of the mixer. L1 and C3, L2 and C4 are the two paralleled LC loads, and they resonate at 2.4 GHz. Although the signals get distortion in the time span, t0 to t1, t2 to t3 and t4 to t5, just like the power ampliﬁers, the use of paralleled LC loads resonating at 2.4 GHz reshapes the output signal and rejects the unexpected interference signals, and the undistorted output waveforms could be obtained. Moreover, from equations (1) and (5), it is clear that, under the same conditions, the conversion gain of the ampliﬁer-based mixer is larger than the conventional Gilbert mixer. 3. POST-LAYOUT SIMULATION RESULTS The proposed ampliﬁer-based mixer is realized using Cadence IC Design Tools 5.1.41 Spectre with standard chartered 0.18-μm RF CMOS technology. According to the 0.18 μm MOSFET Model, the threshold voltage of the NMOS is VthN = 0.42 V, and the threshold voltage of the PMOS is VthP = 0.49 V. The supply voltage of the mixer is 0.8 V, the mixer consumes 1.3137 mA from the 0.8 V supply voltage and the power consumption of the ampliﬁer-based mixer is 1.05 mW. The input IF signal is 20 dBm, and its frequency is 10 MHz; the LO signal is 7 dBm, and its frequency is 2.39 GHz. Figure 5 is the chip layout of the proposed mixer, and it takes a compact chip area of 0.429 mm2 including the testing pads. Based on the layout in Figure 5 and considering the parasitics extracted from the chip layout, the post-layout simulation results are presented in Figures 6–9. Figure 6 is the input third-order intercept point (IIP3) of the proposed mixer, and the IIP3 of the mixer is about 3.82724 dBm. Obviously, from Figure 6, it is clear that the proposed mixer could achieve relatively high linearity. Copyright © 2014 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. 2015; 43:1794–1800 DOI: 10.1002/cta 1798 J. JIN ET AL. Figure 5. The layout of the proposed mixer (0.650 × 0.66 mm2). Figure 6. The IIP3 of the proposed mixer. Figure 7. The transient analysis of the proposed mixer. Copyright © 2014 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. 2015; 43:1794–1800 DOI: 10.1002/cta CMOS, LOW-VOLTAGE LOW-POWER, AMPLIFIER, MIXER 1799 Figure 8. The output spectrum of the proposed mixer. Figure 9. The voltage conversion gain of the mixer. Figure 7 is the transient analysis of the proposed ampliﬁer-based mixer. The input IF signal is chosen as 10 MHz, and its signal level is 20 dBm. The signal in Figure 7 is the output RF signal (VRF = VRF+ VRF), and its frequency is 2.4 GHz. Figure 8 is the output spectrum of the proposed mixer. From Figure 8, it is clear that, the magnitude of the output spectrum of the proposed mixer is 27.79 dB. From Figure 8, it is clear that the output power of the mixer is concentrated at 2.4 GHz, and the other interference signals are relatively smaller. Figure 9 is the voltage conversion gain versus LO power of the proposed ampliﬁer-based mixer. From Figure 9, it is clear that the proposed ampliﬁer-based mixer could provide a relatively large voltage conversion gain when the input LO power changed from 5 to 9 dBm, especially, the ampliﬁer-based mixer could provide 13-dB voltage conversion gain when the LO power is 7 dBm. 4. CONCLUSION A low-voltage low-power 2.4-GHz mixer for ISM band wireless applications is presented in this letter. By inserting the Gilbert switches in the ampliﬁer, a novel LV–LP mixer is achieved. The number of Copyright © 2014 John Wiley & Sons, Ltd. Int. J. Circ. Theor. Appl. 2015; 43:1794–1800 DOI: 10.1002/cta 1800 J. JIN ET AL. stacked transistors of the mixer is one, and the supply voltage is reduced to 0.8 V; The turning on and off the second section of the ampliﬁer is controlled by the Gilbert switches, which reduces the power consumption of the mixer; moreover, the gain of the ampliﬁer is large, and the conversion gain of the ampliﬁer-based mixer is also relatively large. The Cadence IC Design Tools 5.1.41 post-layout simulation results show that the voltage conversion gain of proposed ampliﬁer-based mixer is 13 dB with a LO power of 7 dBm; the supply voltage is 0.8 V, and the power consumption is only 1.05 mW; the whole chip area is only 0.429 mm2. ACKNOWLEDGEMENTS The authors would like to thank Dr. Prof. Angel Rodríguez-Vázquez, Dr. Prof. Mohamad Sawan and the anonymous reviewers for providing valuable comments which helped in improving this manuscript. Engineers Guorong Shen and Yuan Cai in Integrated Circuit Technology and Industry Promotion Center in Shanghai are acknowledged for providing valuable suggestion and discussion of the proposed mixer. The authors would also like to thank Mr. Tomas James Czaban and Mrs. Shanshan Xu in College of Foreign Language of Jishou University for the English improvements of this paper. This work was supported by the National Natural Science Foundation of China (No. 61274020), Science and Technology Planning Project of Hunan Province, China (2014GK3021) and the Research Innovation Project for Graduate in Hunan Province (CX2013B141), China. REFERENCES 1. Alvarado U, Berenguer R, Adin I, Mayordomo I, Vaz A, Bistue G. Low-frequency noise analysis and minimization in Gilbert-cell-based mixers for direct-conversion (zero-IF) low-power front-ends. International Journal of Circuit Theory and Applications 2010; 38(2):123–129. 2. Murad SAZ, Mohamad Shahimin M, Pokharel RK, Kanaya H, Yoshida K. 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