|Publication number||US6940355 B2|
|Application number||US 10/687,679|
|Publication date||Sep 6, 2005|
|Filing date||Oct 17, 2003|
|Priority date||Oct 18, 2002|
|Also published as||CN1708896A, CN1708896B, DE60323253D1, EP1552601A2, EP1552601B1, US20040124931, WO2004036751A2, WO2004036751A3|
|Publication number||10687679, 687679, US 6940355 B2, US 6940355B2, US-B2-6940355, US6940355 B2, US6940355B2|
|Inventors||Seyed-Ali Hajimiri, Roberto Aparicio Joo|
|Original Assignee||California Institute Of Technology|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Non-Patent Citations (3), Referenced by (20), Classifications (9), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims prior to U.S. provisional application No. 60/419,607, filed Oct. 18, 2002, entitled “Distributed Active Transformer Based Oscillators,” which is hereby incorporated by reference for all purposes.
The present invention pertains to the field of oscillators, and in particular to integrated, high frequency voltage controlled oscillators (VCOs).
Integrated VCOs are essential building blocks in phase locked loops, clock recovery circuits, frequency synthesizers, and other circuits used in communication systems. While attempts have been made to fabricate a high frequency VCO on a lossy substrate, such as silicon or silicon germanium, the low quality of inductors used to implement the oscillator tank has limited the phase noise performance of such oscillators. The main cause of low quality in the oscillator tank inductor is the conductive lossy substrate, as a long metal line in a conventional spiral conductor made on the same substrate will be lossy in terms of the power dissipated by the inductor. If the metal line is wide, the capacitive coupling between the metal and the substrate will drain part of the current to the substrate, absorbing a significant portion of the signal power being transmitted across the metal line. On the other hand, if the metal line is made narrow enough to reduce the previous effect to a small level, the overall metal resistance will increase significantly, once more absorbing a significant part of the signal power.
In accordance with the present invention, a circular geometry oscillator is provided that overcomes known problems with high frequency oscillators.
In particular, a circular geometry oscillator is provided that uses slab inductors to reduce signal losses and improve phase noise performance.
In accordance with an exemplary embodiment of the present invention, an integrated VCO is provided. The integrated VCO includes a first slab inductor having two ends and a second slab inductor having two ends. A first oscillator core is connected to a first end of the first slab inductor and a second end of the second slab inductor, and a second oscillator core is connected to a second end of the first slab inductor and a first end of the second slab inductor. In this manner, the low-loss slab inductors provide the oscillator tank inductance.
The present invention provides many important technical advantages. One important technical advantage of the present invention is an integrated, high-frequency VCO that uses low-loss, high-Q slab inductors to provide the oscillator tank inductance, which reduces signal loss and improves phase noise performance.
Those skilled in the art will further appreciate the advantages and superior features of the invention together with other important aspects thereof on reading the detailed description that follows in conjunction with the drawings.
In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures might not be to scale, and certain components can be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness.
VCO 100 includes oscillators 102, 104, 106, and 108, which are connected to each other via slab inductors 110, 112, 114, and 116. As used herein, the term “connect,” and its cognate terms such as “connects” and connected,” can include a connection though a conductor or conducting element, a connection through other associated systems or components, or other suitable connections. As shown, each oscillator 102, 104, 106, and 108, is connected to ground via an associated ground connection 102A, 104A, 106A, and 108A, respectively. Likewise, each slab inductor 110, 112, 114, and 116 has associated inductances modeled as inductors 112A and 112B, 114A and 114B, 116A and 116B, and 118A and 118B, respectively.
Oscillators 102, 104, 106, and 108 can be implemented as NMOS-only cross-coupled oscillators, PMOS-only cross-coupled oscillators, complementary cross-coupled oscillators, noise shifting differential Colpitts oscillators, or other suitable oscillators. At the desired oscillation mode of operation, half of the oscillators operate in a given phase and the other half operate at the opposite phase. Virtual AC grounds and supplies may be created using adjacent opposite phase oscillators such that the supply and ground connections carry only DC current to avoid the capacitive coupling to the substrate at the supply and ground connections. Slab inductors 110, 112, 114, and 116 can be fabricated to be short and wide so as to provide lower loss and higher quality factor, Q, than conventional spiral inductors. Slab inductors 110, 112, 114, and 116 can be rectangular, can be curved, can include one or two turns (such as an “L” shape or a “U” shape), or can have other suitable configurations.
In operation, VCO 100 uses short and wide slab inductors to provide the tank inductance for each of four oscillators that are operating in opposite phases to those oscillators adjacent to them. Suitable oscillator cores can be used to provide the oscillators 102, 104, 106, and 108, so as to provide for the voltage level of a given application, phase noise performance requirements, or other design constraints. In this manner, high frequency voltage controlled oscillators can be provided on a lossy substrate, because the higher quality inductors help to improve phase noise performance of the oscillators. Likewise, connection of the oscillators in a circular configuration forms a virtual AC ground in each corner, and allows the outputs of several oscillators to be combined to decrease their sensitivity to perturbations and thus enhances their phase noise performance.
In addition, coil 310 is provided with output 312 to allow the oscillator signal to be provided to an output. This configuration of coil 310 within the loop formed by slab inductors 110, 112, 114, and 116 forms a transformer with a 1:1 turn ratio. The primary winding of the 1:1 transformer is the output circuit of each of the individual oscillators, and the secondary winding conductors are connected in series with each other and the output. This transformer configuration can be used to provide output impedance matching, to allow balanced or unbalanced operations, to provide DC isolation and power combining of the oscillators for a single output, and to provide other useful functions. In addition, the combined power losses in a VCO using this configuration are lower than those from a VCO that uses conventional spiral transformers.
In operation, VCO 300 allows an oscillator signal to be extracted through the use of a pickup loop operating as a transformer secondary winding, and further provides for the addition of resonant capacitors for each pair of slab inductor terminals to be placed in parallel across a corresponding oscillator.
As shown in
For these prototypes, the oscillator topology chosen was the complementary cross coupled oscillator due to its higher oscillation amplitude and low voltage of operation. The oscillators were also optimized using linear programming.
Although exemplary embodiments of a system and method of the present invention have been described in detail herein, those skilled in the art will also recognize that various substitutions and modifications can be made to the systems and methods without departing from the scope and spirit of the appended claims.
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|U.S. Classification||331/2, 327/46|
|International Classification||H03B1/00, H03L7/099, H03B5/18|
|Cooperative Classification||H03B2201/0208, H03L7/099, H03B5/1852|
|Oct 17, 2003||AS||Assignment|
Owner name: CALIFORNIA INSTITUTE OF TECHNOLOGY, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HAJMIIRI, SEYED-ALI;JOO, ROBERTO APARICIO;REEL/FRAME:014625/0783
Effective date: 20031016
|Mar 11, 2004||AS||Assignment|
|Feb 27, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Mar 7, 2013||FPAY||Fee payment|
Year of fee payment: 8