A Sub-0.75RMS-Phase-Error Differentially-Tuned Fractional-M Synthesizer with On-Chip LDO Regulator and Analog-Enhanced AFC Technique Lei Lu,Lingbu Meng,Liang Zou, Hao Min and Zhangwen Tang Fudan University,Shanghai,China
A Sub-0.75°RMS-Phase-Error Differentially-Tuned Fractional-N Synthesizer with On-Chip LDO Regulator and Analog-Enhanced AFC Technique Lei Lu, Lingbu Meng, Liang Zou, Hao Min and Zhangwen Tang Fudan University, Shanghai, China
Outline 。Motivation ·System Architecture Level Shifter for Symmetrical Tuning Curves High-PSR LDO Regulator Digital AFC with Monitor 。Measured Results 。Conclusions 2
2 Outline • Motivation • System Architecture • Level Shifter for Symmetrical Tuning Curves • High-PSR LDO Regulator • Digital AFC with Monitor • Measured Results • Conclusions
Motivation Symmetrical tuning curves Level Shifters eliminate threshold voltage Large noise from power supply deteriorates VCO severely High-PSR LDO Regulator Frequency drift due to temperature variation Control Voltage monitor to restart AFC 3
3 Motivation • Symmetrical tuning curves – Level Shifters eliminate threshold voltage • Large noise from power supply deteriorates VCO severely – High-PSR LDO Regulator • Frequency drift due to temperature variation – Control Voltage monitor to restart AFC
Single-Ended Tuned Synthesizer ZF(s) Kvco=△fvcol△Ve PFD Charge Pump Filter Divider DSM IcpZF(S)Kvco open-loop gain三 2TTN Advantage:Single-ended CP and VCO Disadvantage:Susceptible to CM noise, large LPF area
4 Single-Ended Tuned Synthesizer • Advantage: Single-ended CP and VCO • Disadvantage: Susceptible to CM noise, large LPF area Divider PFD Charge Pump DSM fref fvco Icp Kvco =Δ fvco/Δ Vc Loop Vc Filter Z F(s) N 2 π N open-loop gain Icp Z F(s) Kvco VCO
Differentially Tuned Synthesizer 0.5lcp ZF(s) Loop KvCo=AfvCoA(Vcp-Vcn) Charge Filter cp PFD Pump cn Filter -0.5Icp Divider DSM open-loop gain I0.51cp（-0.5p】☑(s)Kvco 2TTN Advantage:Immune to CM noise,small LPF area (differential LPF) Disadvantage:differential CP and VCO 5
5 Differentially Tuned Synthesizer Kvco = Δ fvco/Δ ( Vcp – Vcn ) Divider PFD Charge Pump DSM fref fvco Vcp Z F(s) N Loop Filter Loop Filter Vcn 0.5 Icp –0.5 Icp Z F(s) [0.5 Icp–(–0.5 Icp)] ZF(s) Kvco 2 π N open-loop gain VCO • Advantage: Immune to CM noise, small LPF area (differential LPF) • Disadvantage: differential CP and VCO
Synthesizer Block Diagram 8 Digital AFC Band Shift Level Shift cpo re Voltage /co PFD div Monitor C: /CO R Level cno S2 Shift Differential LPF cn Differential CP Divider DSM 6
6 Synthesizer Block Diagram Differential LPF PFD Digital AFC fref R1 R1 C1/2 C2 C2 R3 R3 C 3 C 3 Vref s1 s1 s 2 s 2 Differential CP up upb dn dnb Level Shift Vref s1 s1 Vcp Vcn Vcpo Vcno Divider DSM N fvco 8 Band Shift VCO LDO fdiv Voltage Monitor Level Shift
Simplified differential LC-tank Differential tuning of VCO -Inversion MOS transistors as varactors n-type /-MOS varactors p-type /-MOS varactors fixed capacitors 7
7 Simplified differential LC-tank • Differential tuning of VCO – Inversion MOS transistors as varactors Vop L Von Vcn Vcp n-type I-MOS varactors p-type I-MOS varactors fixed capacitors
Conventional Differentially Tuned Techniques Vocm=(Vop+Von)/2 p Vthn Vecm=(Vep+Ven)/2 ocm Vocm=(Vop+Von )2 好 op Vocm 8
8 Conventional Differentially Tuned Techniques Vccm=( Vcp + Vcn)/2 Vthn Vthn Vop Von Vcn Vcn Cn Vocm Vthn |Vthp| Vop Von Vcp Vcp Cp |Vthp| Vocm |Vthp| Vocm=( Vop + Von)/2 Vocm=( Vop + Von )/2
Asymmetrical Tuning Curves Inversion MOS varactors have both p- type and n-type Better choice in differentially tuned VCO than accumulation transistors Lead to asymmetrical tuning curves even if Vccm is equal to Vocm [See Soltanian,et al.,CICC'06] The middle point of tuning curves deviates from Vocm by Vthn+|Vthpl
9 Asymmetrical Tuning Curves • Inversion MOS varactors have both ptype and n-type – Better choice in differentially tuned VCO than accumulation transistors • Lead to asymmetrical tuning curves even if Vccm is equal to Vocm [See Soltanian, et al., CICC’06] • The middle point of tuning curves deviates from Vocm by Vthn+| Vthp|
Proposed Differentially Tuned Techniques with Level Shifters Vocm-Vthn+Vgsn=Vccm Level Shifter ocm-V thn+Vgsn cn Cp 个Vocm+|Vthpl Vgspli三Vccm Vocm+Vihpl-Vgspl Vep 10
10 Proposed Differentially Tuned Techniques with Level Shifters Vcn Vthn Vthn Vop Vcno Von Vgsn |Vthp| Vop Von Vcpo |Vthp| Vcp |Vgsp | Level Shifter Vcn C n Vocm–Vthn+Vgsn Vcp C p Vocm +|Vthp|–|Vgsp | Vocm–Vthn+Vgsn=Vccm Vocm +|Vthp|–|Vgsp|=Vccm