tailieunhanh - Advanced Microwave Circuits and Systems Part 8

Tham khảo tài liệu 'advanced microwave circuits and systems part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 204 Advanced Microwave Circuits and Systems 1 1 -------7 --------7 Z Vx g m1 sCds gm2 sCgs ln Ix 1 sCgd - g m1 sCgd - gm2 g m1 sCds gm 2 sCgs 2 If the transistors size are the same we can assume that gm1 gm2 gm and Cgs Cds for microwave range in simplified calculation with small dimension device 12 . The Eq. 2 becomes as following 2 Z - gm 2sCgd sCds 3 If s jữ is used then Eq. 3 can be written as following Zn -2gm - . 2 2Cgd Cds gro2 2 2Cgd Cds gw2 2 2Cgd Cds 4 If Eq. 4 Zln Ra - jCa then Ra and Ca can be expressed as R -2 gm__ C 2a 2Cgd Cds a gm2 ữ 2 2Cgd Cds 2 a gm2 2 2Cgd Cs 2 where Ra is the real part and Ca is the imaginary part respectively. And the parameters of active device are represented in Fig. 7. Fig. 7. Parallel LC oscillator model Implementation of Low Phase Noise Wide-Band VCO with Digital Switching Capacitors 205 When the parasitic is ignored the traditional negative resistance of the input port is indicated by -2 gm. Although the complementary topology has more devices than the NMOS pair the differential voltage swing is larger for the same current consumption resulting in reduce phase noise. The M1 M4 transistors of a complementary cross-coupled pair are shown in Fig. 4 which yield 9 9 a a s s. go mn o mp J negative resistance to compensate the passive element loss of LC tank. It can be achieved to start up for oscillation 13 and output signals of the circuit are differential. Switching tail current The circuit with a tail current can improve the effect of various noise sources and supply sensitivity 11 and some researchers discovered that a square wave cycling a MOS transistor from strong inversion to accumulation reduces its intrinsic 1 f noise 14 . Therefore switched biasing can be useful in many circuits to reduce the up-conversion of noise 1 f 15 . The flicker noise from tail current source especially in MOSFET transistors makes a great deal of phase noise. Gradually switching tail transistors can release trapped .