Implementation of Low Phase Noise Wide-Band VCO with Digital Switching Capacitors
ABSTRACT This VCO presents a technique of operating narrowband into wideband, employs switching tail current technique and maintains the good phase noise performance. The switching capacitor modules offered multi-channels can enhance oscillator frequency range and the KVCO is still small. This VCO operated from 3.64 to 5.37 GHz with 38% tuning range. The power consumption is 13.7 mW by a 1.8 V supply voltage and measured phase noise in all tuning range is less than -122 dBc/Hz at 1 MHz offset.
Conference Proceeding: A 1.3-2.8 GHz Wide Range CMOS LC-VCO Using Variable Inductor[show abstract] [hide abstract]
ABSTRACT: This paper proposes a novel wide-range tunable CMOS voltage controlled oscillator (VCO). VCO uses an on-chip variable inductor and switched capacitors as variable elements. The VCO was fabricated using a standard 0.18mum CMOS process with five metal layers. The oscillation frequency can be tuned from 1.28 GHz to 2.75 GHz with tuning range of 72%. The proposed VCO operates with low phase noise, and it achieves high FOM<sub>T</sub> -205.9 dBc/HzAsian Solid-State Circuits Conference, 2005; 12/2005
Conference Proceeding: A 0.8 V 5.9 GHz wide tuning range CMOS VCO using inversion-mode bandswitching varactors.International Symposium on Circuits and Systems (ISCAS 2005), 23-26 May 2005, Kobe, Japan; 01/2005
- [show abstract] [hide abstract]
ABSTRACT: In this paper, a 1-V 3.8 - 5.7-GHz wide-band voltage-controlled oscillator (VCO) in a 0.13-μm silicon-on-insulator (SOI) CMOS process is presented. This VCO features differentially tuned accumulation MOS varactors that: 1) provide 40% frequency tuning when biased between 0 - 1 V and 2) diminish the adverse effect of high varactor sensitivity through rejection of common-mode noise. This paper shows that, for differential LC VCOs, all low-frequency noise such as flicker noise can be considered to be common-mode noise, and differentially tuned varactors can be used to suppress common-mode noise from being upconverted to the carrier frequency. The noise rejection mechanism is explained, and the technological advantages of SOI over bulk CMOS in this regard is discussed. At 1-MHz offset, the measured phase noise is -121.67 dBc/Hz at 3.8 GHz, and -111.67 dBc/Hz at 5.7 GHz. The power dissipation is between 2.3 - 2.7-mW, depending on the center frequency, and the buffered output power is -9 dBm. Due to the noise rejection, the VCO is able to operate at very low voltage and low power. At a supply voltage of 0.75 V, the VCO only dissipates 0.8 mW at 5.5 GHz.IEEE Transactions on Microwave Theory and Techniques 09/2003; · 2.23 Impact Factor
Implementation of Low Phase Noise Wide-Band VCO with Digital Switching Capacitors 199
Implementation of Low Phase Noise
Wide-Band VCO with Digital
Meng-Ting Hsu, Chien-Ta Chiu and Shiao-Hui Chen
Microwave Communication and Radio Frequency Integrated Circuit Lab
National Yunlin University of Science and Technology,
Department of Electronic Engineering
Yunlin, Taiwan, Republic of China
In present fast-growing wireless communications, requires wide bandwidth, low-power and
low-cost RF circuits . In Fig. 1, it is a simple super-heterodyne transceiver , and in this
diagram, VCO (voltage-controlled oscillator) is one of the most important building blocks in
the wireless communication system. An optimum performance VCO should include low
phase noise and wide bandwidth to support several communication standards of wireless
transceiver, and low power design technique to enhance the battery lifetime. Recently, the
standard CMOS process technology is better choice to overcome low-cost challenge. The
choice is also favored by the possibility of system-on-chip integration with digital parts,
which should save the total chip area and cost. The VCO with multi-band and wideband are
the current trend  - . The methods of increasing tuning range are classified as follows,
switching inductors or variable inductor , switching capacitor modules , , varactors
in parallel ,  and capacitive source degeneration . It is a well-known fact that the
Lesson's model of the single-sideband power spectral density is given by :
Where FKT is the effective thermal noise with the multiplicative factor F , Boltzmann's
constant K, the absolute temperature T; PS is the average power dissipated in the resistive
part of the tank; Aft is the offset frequency; QL is the effective quality factor of the tank and
is dominated by quality factor of spiral inductor;
is the center frequency and
the corner frequency of the flicker noise. The model describes well the shape of the
spectrum, and realizes that many parameters affect phase noise performance. Circuit design
tradeoff of the device parameters is required.
Advanced Microwave Circuits and Systems200
Fig. 1. Building blocks of super-heterodyne transceiver 
2. VCO Design
VCO must be designed carefully, its performance affects the stability of the VCO in the
transceiver. This section studies how to optimize the circuit design and establish the design
procedure for a voltage-controlled oscillator (VCO) in the front end of a transceiver. It
promotes the better quality of communication by decreasing the power dissipation and
phase noise. This VCO has good data performance between the simulation and
Fig. 2. Design flow of VCO
Implementation of Low Phase Noise Wide-Band VCO with Digital Switching Capacitors201
2.1 Design flow of VCO
This VCO was made by TSMC (Taiwan Semiconductor Manufacturing Company) standard
0.18|μm 1P6M CMOS process technology. In Fig. 2, design process can be divided into the
following steps: Step 1: Review of related literature, and make design specification. Step 2:
Design passive and active circuit of the VCO topology.
Step 3: It is pre-simulated by Agilent Advanced Design System (ADS) with TSMC 0.18|µm
RF CMOS process model and fabricated by TSMC 0.18|µm CMOS technology. It is need to
redesign if the pre-simulation result and design goal are different.
Step 4: IC layout design using cadence virtuoso and laker.
Step 5: Layout verification using Calibre DRC (Design Rule Check) and LVS (Layout Versus
Step 6: Using the EM simulator with ADS Momentum to perform a numerical
electromagnetic analysis of the layout. It is
need to re-layout if the post-simulation and pre-simulation results are different.
Step 7: The chip is fabricated by TSMC (Taiwan Semiconductor Manufacturing Company)
0.18|μm 1P6M standard CMOS process technology.
Step 8: The chips are measured on PCB board or on-wafer.
2.2 Simple LC Tank VCO Structure
In Fig. 3, we can analyze several important parts of this simple LC tank VCO structure:
The part A-LC tank: The tank circuit consists of a high-Q inductor and varactor components.
Select the model values of inductor and varactor for control oscillatory frequency. Where, Rp
denotes the passive element loss of LC tank. The part B-Active circuit: Active circuit is used
to provide negative resistance to compensate for the loss of the LC tank. The part C-Buffer:
The buffer is designed to drive the 50 ohm load of the testing instruments.
Fig. 3. Simple LC tank VCO structure
Advanced Microwave Circuits and Systems202
2.3 Schematic of the proposed VCO
In Fig. 4(a) shows the narrowband VCO which is composed of the complementary cross-
coupled pair MOSFETs, LC tank and switching tail current transistors. In addition, we add
the switching capacitor modules for wideband application in Fig. 4(b). A wide-tuning range
VCO usually accompanies large Kvco (gain of VCO, Kvco=doo/dVtune). But large Kvco of
VCO will amplify noise on the control node (Vtune) and hence will degrade the phase noise
performance. We design the small size of PMOS varactors which are capable of providing a
small gain of VCO, an array of binary switching capacitor modules were used to extend the
tuning range. In this section we discuss several components such as complementary cross-
couple pair, LC tank, switching tail current and switching capacitor modules.
Fig. 4. Circuit schematics of (a) narrow band VCO without switching capacitor modules; (b)
wide band VCO with switching capacitor modules
2.3.1 Complementary cross-couple pair
There are three merits in the complementary cross-coupled pair which described as follows :
A. Same current existing, the complementary cross-coupled pair offers higher
transconductance and faster switching speed on each side.
Implementation of Low Phase Noise Wide-Band VCO with Digital Switching Capacitors203
B. The output wave are more symmetrical on each other for rise-time and the fall-time, as
debate the noise which comes from low frequency noise, 1/f, transferring to high frequency.
C. In all NMOS structure, the channel voltage is larger than complementary case, Therefore,
it causes faster saturation speed and larger y value .
The simple schematic of NMOS cross-coupled pair is shown in Fig. 5. T1 and T2 indicate
NMOS transistors. The high frequency equivalent circuit with capacitive parasitic is shown
in Fig. 6(a). And the calculation of input impedance or admittance of the simplified
equivalent circuit is shown in Fig. 6(b).
Fig. 5. Simplified schematic of NMOS cross coupled pair
Fig. 6. Small signal model of Fig. 5 for (a) high frequency equivalent circuit; (b) equivalent
circuit of impedance calculations
/ /,/ /,
gdgdgd gsgs gs
We can obtain the input impedance Zin as following:
for simple calculation of