Chapter 3 Design of Low-Power Current-Reused CMOS VCO
3.3 VCO Simulation and Measurements For L-Band System
3.5.3 WiMAX FWA VCO Measurement Characteristics
In this section, The Measurement results demonstrate that central oscillation signal of 3.2 GHz with the 500 MHz turning range, 2.82 to 3.35 GHz but in this case. We got some VCO steady problem in phase-noise. we will discuss late, About power-consumption which we trade-off between power-consumption and phase-noise. Usually we hope to get as low phase-noise as possible. So we expense some power-consumption to get lower phase-noise and the VCO core is about 6.15 mW.
(a)
(b)
Figure 3.28 Measurement result of WiMAX FWA current-reused VCO spectrum (a) Normal state (b) frequency per 2 by divider
Show illustration 3.28 (a) (b) and 3.29, we can see very dirty spectrum in Figure 3.28(a) (b) that occurred acute of signal frequency and the target frequency variation form
0.5M~1MHz. So we can’t get stable frequency to Measurement phase-noise during our Measurement. By above reason, we conjecture that due to we used too long-length
interconnect to connect body to Vbody PAD(ref. figure 3.26) which pass through and too close inductance , signal output line and inductance Guard.-Ring that made much noise-signal coupling to capacitor to MOS’s body and direct influence circuits. Show Figure.3.29 that result to show no frequency locked and instrument can’t find real center carrier frequency to plot normal tendency of phase-noise.
Figure 3.29 Measurement phase-noise-instable result of WiMAX FWA current-reused VCO
Figure 3.30 Measurement turning range result of WiMAX FWA current-reused VCO
Figure 3.31 Measurement Vtune V.S. current result of WiMAX FWA current-reused VCO
Figure 3.32 Measurement output power result of WiMAX FWA current-reused VCO
Show Figure 3.31 and 3.32 VCO Vtune V.S. current /output power (dBm) respectively that had very close result with simulation.
Table 3.15 Simulation and Measurement results of WiMAX FWA VCO
Simulation Measurement
Spec. Result
Voltage
1.5 V 1.5V
Current(core)
3.96mA 4.1mA
Frequency
3.341~3.912GHz 2.82G-3.35G
Output
power_Pout.(dBm)
-8.37dBm -8 ~ -10dBm
Power consumption
(total)
5.53mW 6.15mW
Turning Range
15.74% 16.73%
Phase-Noise@100KHz
-101.17 - X (instable)
Phase-Noise@1MHz
-123.46 - X(instable)
FOM
-187.56_1M_3.91G
-186.19_1M_3.34G - X(instable)
Die Size 1.13 X 1.05 mm
3.6 Discussion and Summary
Two different bands Current-Reused Configuration of VCO are introduced in this chapter. In above sections, the Current-Reused Configuration can use one path current to get half power-consumed that difference than convention VCO [6] two path currents. In the phase-noise characteristic, we optimize inductance Q factor and find the maximum value that
not only can got most sharp spectrum but also got good phase-noise. The Low-Power CMOS Voltage-controlled oscillator (VCO) had built by current-reused configuration with Output-Buffer fabricate by TSMC 0.18μm mixed signal/RF 1P6M process. A Good performance was Measurement with this design. The VCO circuit resonator was application on 1.24G~1.46G and 2.82G-3.35G 2.21~2.39 GHz respectively, the turning voltage two VCO both bias voltage between 0 to 1.8 V, Output power -3.37dBm and -8dBm and phase-noise -125.35 dBc/Hz at 1-MHz offset frequency(L-band). The power consumption of the VCO (core) only 1.8mW at 1.2V and 6.15mW at 1.5V voltage supply.
Figure 3.33 Discusser layout of WiMAX FWA current-reused VCO MOS body
Interconnect line of Vbody
1
2
3
Three fail reasons are shown in Figure 3.33. The fail resins we conclude are unsuitable position of interconnection line. In our comment, that reason 1(square_no.1): VCO output signal coupling to Vbody interconnect line and noise pass through into P-MOS capacitor.
Reason 2(square_no.2): The inductance Guard-Ring connects to ground not average in this case and Guard-Ring is use M1 connect to ground, our body interconnect line also the same that. So noise very easy coupling to there. Reason 3(square_no.3): This is M1 to M6 coupling capacitance. In this case, we neglect that effect in parasite extraction at EM-simulation and that by reason 1 and 2 maybe output signal and guard-ring noise also coupling to LC resonator. Form above reasons, instable and shift frequency maybe by that.
Therefore, above Noise Current experiment prove our problem point at this issue.It is shown in Figure 3.34. It is injected 50
μ
A current noise into body pad.Figure 3.34 Noise Current experiment for proving instable oscillation
The simulation results can refer to Figure 3.36 and normal state shown in Figure 3.35.
Normal State
Figure 3.35 Noise Current experiment for proving instable oscillation-normal state Noise Injected (Noise_50
μ A)
Figure 3.36 Noise Current experiment for proving instable oscillation-noise injected Shown in Figure 3.35 .The turning range is from 3.85GHz to 3.25GHz and has regular output spectrum at no-noise injected state. We can refer to Figure 3.36 when has been
3.61G
3.85G
injected 50
μ
A noise current which influence circuit regular oscillation, turning range became form 3.61GHz to 3.24GHz and has deformed spectrum maybe is reason of instable which the difference in frequency between the normal and the noise injected there is 240MHz and has 150MHz frequency inaccuracy in our substrate. In above proved to result between simulation and Measurement.Chapter 4
Design of Low-Power Current-Reused with Balance Resistors CMOS VCO
4.1 Induction of Current-Reused VCO with Balance Resistors Structure
Figure. 4.1 shown the architecture of Current-Reused Configuration with balance resistors Included Output-Buffer VCO.Figure.4.1 The Current-Reused Configuration with balance resistors topology. Rbr
(balance resistors topology negative impedance) could be derived as equation (4.1) [7] and assume gmp equal gmn could be derived as equation (4.2).
Figure.4.1 Schematic of the Current-Reused Configuration with balance resistors Include Output-Buffer VCO
( 1/ ) ( 1/ )
This replace resistor makes NMOS direct-connect to ground which is not only remove the body effect but also enhance negative feed-back. In other way, the balance resistors can balance MOS on/off-time status. The buffer use common-Source stage to make sure output is 50-Ohm match and quarantines DC current leak out.
4.2 Design of Current-Reused VCO with Balance Resistors for WiMAX WSC System
The WiMAX (Mobile worldwide interoperability for microwave access) is a wireless standard that introduces orthogonal frequency division multiple access (OFDMA) and other key features to enable mobile broadband services at a vehicular speed of up to 120 km/h.
WiMAX complements the and competes with wireless local area networks (WLANs) and the third generation (3G) wireless standards on coverage and data rate. The WiMAX standard supports both fixed and mobile broadband data services[18]. That means have a much larger market in this field.
4.3 Current-Reused VCO with Balance Resistors VCO Simulation and Measurement
In this section, a 1.2V Low-Power CMOS Voltage-controlled oscillator (VCO) build by current-reused configuration with Output-Buffer and two drain resistors used in order to improve magnitude symmetry of output signals for IEEE 802.16e, by TSMC 0.18μm mixed signal/RF process. A Good performance was measured with this design. The VCO circuit resonator was applied between 2.21~2.39 GHz under the turning voltage between 0 to 1.2 V 、 Output power -4.2dBm and phase-noise -121dBc/Hz at 1-MHz offset frequency. The power consumption of the VCO only 3.96mW at 1.2V voltage supply with buffer included.
4.3.1 Design of Structure
The relate of product will present the Mobile WiMAX standard. In this Paper The VCO application in IEEE 802.16e WMAX Wireless Communication Services (WCS) under 2.21~2.39 GHz coverage 2.305-2.320GHz, 2.345-2.360GHz of WCS.
In mobile and portable communication equipment the supply voltage should be as low as possible. To increase equipment operating time, this shows how importance of low-power circuits. A voltage controlled oscillator (VCO) is an important block among the blocks of any transceiver that applied in mobile and portable equipments.
In wireless transceivers, VCO the power mostly consume the power mostly. VCOs implemented in silicon-based technologies are mainly realized as differential cross-coupled topologies due to the poor substrate isolation properties of silicon based technologies. In this paper, the proposed VCO uses P-MOS and N-MOS transistors in the cross-connected pair.
The P and N-MOS can be reduced by half supply current and two drain resistors not only improve magnitude symmetry of output signals but also improving negative conductance. It can be improved better than degeneration source resistors [7].
Figure.4.2 Schematic of the Current-Reused Configuration with balance resistors Include Output-Buffer VCO, design by ADS
4.3.2 WiMAX WSC System VCO Simulation Characteristics
The study of circuit simulated, analyzed and extract layout parasitic by Agilent-ADS software. The VCO core operates voltage, current, power-consumed, 1.2V and 360uA, 0.43mW respectively, output power is -4.55dBm, operation frequency 2.264~2.74GHz and Phase-noise -124 dBc/Hz offset frequency at 1M. The Goal is low power-consumed.
Shown in Figure 4.3 oscillation frequency at 2.44 Ghz and has -17.04 dBm 2nd harmonic error value. Figure 4.4 turning range is from 2.36 GHz to 2.72 Ghz. The phase noise 100 KHz and 1MHz offset are -103.42 dBc/Hz and -124.02 dBc/Hz respectively. The total specifications are shown in Table 4.1.
In Table 4.2 and 4.3 are manufacture process and temperature variation respectively.
The simulation are little variation results that can be accepted.
Shown in Figure 4.8 oscillation frequency at 2.42 Ghz and has -16.32 dBm 2nd harmonic error value. Figure 4.4 turning range is from 2.36 GHz to 2.72 Ghz. The phase noise 100 KHz and 1MHz offset are -99.14 dBc/hz and -120.49 dBc/hz respectively. The total specifications are shown in Table 4.4
The post/pre simulation specifications are shown in Table 4.5 and Table 4.6 reference of VCO compare. Shown In Figure 4.11 and 4.12 are layout and microphotograph of VCO respectively.
( No manufacture process variation and interconnect effect )
Transient Characteristics
Figure.4.3 Transient simulation of WiMAX WSC current-reused VCO
Harmonic Characteristics Turning Range
Figure.4.4 Turning range simulation of WiMAX WSC current-reused VCO
Phase-noise ：
Figure 4.5 Phase-noise simulation of WiMAX WSC current-reused VCO
Table 4.1 WiMAX WSC current-reused VCO of simulation specifications
Operation Voltage 1.2 V
Operating Frequency 2.36GHz ~2.72GHz
Turning Range 14.18%
Power consumption
(core) 0.432mW#
Power consumption
(Buffer) 1mWPout.(dBm) -4.5
Phase-Noise@100KHz (dBc/Hz) -103
Phase-Noise@1MHz(dBc/Hz) -124
(#) Power consumption(Buffer) Total of two side buffer power-consumed
(Manufacture process variation)
Table 4.2 Manufacture process variation of WiMAX WSC current-reused VCO
Manufacture process variation results (#) Power consumption(Buffer) Total of two side buffer power-consumed
(Temperature variation)
Table 4.3 Temperature variation of WiMAX WSC current-reused VCO
Temperature variation results
(#)
Power consumption(Buffer) Total of two side buffer power-consumed(With interconnect line effect - Post Simulation)
Figure 4.6 Interconnect lines extraction of WiMAX WSC current-reused VCO
Figure 4.7 Interconnect lines extraction of WiMAX WSC current-reused VCO for layout
Post-simulation result:
Transient Characteristics
Figure 4.8 Transient post-simulation of WiMAX WSC current-reused VCO
Harmonic Characteristics Turning Range
Figure 4.9 Turning range post-simulation of WiMAX WSC current-reused VCO
Phase-Noise
Figure 4.10 Phase-noise post-simulation of WiMAX WSC current-reused VCO
Table 4.4 Temperature variation of WiMAX WSC current-reused VCO
Operation Voltage 1.2 V
Operating Frequency 2.364GHz ~2.724GHz
Turning Range 14.18%
Power consumption
(core) 0.418mW#
Power consumption
(Buffer) 0.99mWPout.(dBm) -4.6
Phase-Noise@100KHz (dBc/Hz) -99
Phase-Noise@1MHz(dBc/Hz) -120
(#) Power consumption(Buffer) Total of two side buffer power-consumed
Table 4.5 WiMAX WSC current-reused VCO Results of Post-simulation and pre-simulation
Post-simulation Pre- simulation
Operation Voltage 1.2 V 1.2 V
Operating Frequency 2.36GHz ~2.72GHz 2.26GHz ~2.74GHz
Turning Range 14.18% 18.51%
Power consumption
(core) 0.418mW 0.432mW#
Power consumption
(Buffer) 0.99mW 1mWPout.(dBm) -4.6 -4.5
Phase-Noise@100KHz
(dBc/Hz) -99 -103
Phase-Noise@1MHz(dBc/Hz) -120 -124
(#) Power consumption(Buffer) Total of two side buffer power-consumed
Table 4.6 reference of WiMAX WSC current-reused VCO Results compare
PDC Pout.
Ref. supply
voltage Technol. Freq. Turning Range
Measurement 1.2V CMOS
90-nm 5.6 Ghz 9.50% 0.52mW -3 N/A -112
Figure 4.11 Layout of WiMAX WSC current-reused VCO
Figure 4.12 Microphotograph of WiMAX WSC current-reused VCO
4.3.3 WiMAX WSC System VCO Measurement Characteristics
In this section, we will discuss measurement results. The measurement results demonstrate the central oscillation signal of 2.29 GHz to be associated with the 180 MHz turning range, 2.2 to 2.39 GHz and -120 dBc/Hz phase noise at 1 MHz offset. The power consumption of the VCO core is only 3.96 mW. The measurement result evaluated by means of a figure of merit factor is -180.87 dBc/Hz by equation (3.2).
.
Figure 4.13 Measurement Phase-noise result of WiMAX WSC current-reused VCO
Figure 4.14 Measurement current result of WiMAX WSC current-reused VCO
Figure 4.15 Measurement turning range result of WiMAX WSC current-reused VCO
Figure 4.16 Measurement spectrum result of WiMAX WSC current-reused VCO
Figure 4.17 Microphotograph of wire bounding VCO
Figure 4.18 CPW transmission line structure layout
Figure 4.19Measurement result of WiMAX WSC current-reused VCO waveform
Using CPW transmission line structure layout is shown in Figure 4.18, Figure 4.17 wire bounding on FR4 PCB and Figure 4.18 is measurement result for waveform by Agilent 54855A Oscilloscope which very well phase only 0.7 degree inaccurately.
Table 4.7 Simulation and measurement of WiMAX WSC Results
Simulation Measurement
Frequency 2.661GHz ~2.37GHz 2.39~2.2GHz
Output-power P
out.(dBm) -5 dBm -3.4dBm~-4.2dBm
Power consumption (total) 0.432mW, 1.85mW
(core, with buffer) 3.96~4.668mW
Turning Range 11.57% 7.86%
Phase-Noise@100KHz -99 -91~-83
Phase-Noise@1MHz -120 -117~-120
FOM (power with buffer) -184.82(1.836mW)@1M -180.87(3.96mW)@1M
Die Size 1.24 X 1.11 mm
4.4 Discussion and Summary
We introduced a Current-Reused Configuration with balance resistors Included Output-Buffer VCO Circuit techniques. In above sections, we knew that VCO has very simple structure and good performance in measurement results. But that has some performance limitation that maybe can fix by other techniques like relate of ISF fix techniques, custom inductance (High Q factor) and new VCO structures overcome
A 1.2V Low-Power CMOS Voltage-controlled oscillator (VCO) had built by current-reused configuration with Output-Buffer and two drain resistors used in order to improve magnitude symmetry of output signals for IEEE 802.16e, by TSMC 0.18μm mixed signal/RF process. A Good performance was measured with this design. The VCO circuit resonator was applied between 2.21~2.39 GHz under the turning voltage between 0 to 1.2 V , Output power -4.2dBm and phase-noise -120dBc/Hz at 1-MHz offset frequency. The power consumption of the VCO only 3.96mW at 1.2V voltage supply with buffer included.
Chapter 5
Conclusions and Future works
5.1 Conclusions
Three chips of low power integrated CMOS VCO has been designed using in L-band, WiMAX application respectively. Those VCO are based on a low power-consumption architecture using a TSMC 0.18um RF mixed signal 1P6M CMOS process. The first types are 1.8V/1.5V standard current reused topology and second type is current reused with two balance resistors topology VCO. Those topologies have low power-consumption characteristic.
In this thesis, the VCO was designed based on current reused topology. We had finished three chips, that L-band, WiMAX WSC and WiMAX FWA which those are work well except WiMAX FWA chip that has very serious frequency shift problem and it had been discussed in above section. Those chip have good performance which output signal power -4.2 / -8~-10 dBm, power-consumed 1.85mW/3.3mW(with buffer)/6.15mW respectively and under -120 dBc/Hz phase-noise.
5.2 Future Work
Generally, the substrate parameter is major cause of frequency shift problem. In our study, we can make sure 0.1GHz shift at last fitting substrate parameter version but maybe layout skill also influence frequency shift in WiMAX FWA, which is very important and must be considered carefully in related layout.
The Q factor is key parameter of inductance in the design VCO about phase-noise characteristic. For example, the parameter QFWA is Shown in Figure 5.1. The Q factor has been optimized which had good represented on phase noise in chapter 3.The Customize inductor or transformer is different requirement for any different applications.
Figure.5.1 Inductance Q Factor of three Chip
For example, with 4 port and 6 port transform can reduce area and can be used for higher frequency application up to 20GHz. By the way, high Q inductance can be used for filter or VCO. The high Q is the key parameter in the design of VCO circuits. Without a high Q value for the inductor, the circuit performance cannot be improved significantly. Therefore, the design of high quality inductors is a major task for RF application.
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