tailieunhanh - Ultra Wideband Part 7

Tham khảo tài liệu 'ultra wideband part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 174 Ultra Wideband Q roL Ì eq 1- r2 c L - ro 2L C eq eq eq eq eq I Req _ . . . 2 . 1 R G 1 roL R eq eq eq eq 13 zm Req jaLeq eq eq 1 ReqGeq - LeqCeq Ì ReqCeq LeqGeq 14 Clearly with decreasing Req the quality factor is improved. Note that in conventional TAI topology Vb constant see Figure 16 a . As can be seen from equations 10 11 and 13 active resistor has direct effect on increasing Leq and Req. However this increase in Req will degrade the quality factor. To overcome this problem Vb can be utilized as the extra tuning voltage to control the gds of transistor M2. Thus the required inductance and quality factor are achieved by controlling Vtune and Vb simultaneously. For further enhancement of quality factor and inductance one can utilize the transistor M5 in parallel with feedback resistance Rf as shown in Figure 17 b 18 . This transistor which operates in the cut-off region exhibits a frequency dependent capacitance as shown in Figure 17 c . Using a CMOS technology a tunable resistance from 100 to kfí may be achieved 18 for Vtune to Vtune as illustrated in Figure 17 a . 0 2 4 6 8 10 12 14 16 freq GHz . _ c 17. a Variation of effective resistance versus tuning voltages b Proposed active resistance with parallel MOSFET c Variation of capacitance in proposed active resistance versus frequency. Fig. The values of each component of equivalent circuit model are expressed below Cp is equivalent capacitance of M5 r _r 2 ữC pReff g ds 2 Rejfgds 2 1 Reff C p P effSds 2 2 g ds 2 C C ---------------------------------------------------------------------- eq gs 3 C- 2 Reff 2 15 Ultra wideband oscillators 175 Req Leq 2aCpReffgds 2 Reffgds2 1j Reffgds2 2gds 2 G ------------------ -------------------- eq 2 gm1gds2gds3 ro gm2Cgs1 Cgs1Cgs2 1 2 o C 2 Ref2 gm1CpCgs1Reff gds2 n n n gm1 1 -------------- d . 2 - 2 2 gm1 I 2 - 2 2 1 Cp Reff I 1 Cp Reff 2 2 2 gm1 gm2gm3 gm2gm3Cgs1 gm1gm2Cgs1 ro Cgs1Cgs2 gm1CpReff gds2 -1 2 2 2 gm1Cgs1 1 Cp R eff M - Reffgds2 1 1a. .