Patent Application
20120068745
The present invention relates to electrical circuits, and more particularly to injection-locked frequency dividers.
Millimeter-wave frequency typically refers to the frequency band between 30 and 300 GHz. Within this frequency range, the wavelength of electromagnetic signals is small. Since the device size of passive component is usually in proportion to the wavelength, the passive element at millimeter-wave frequencies becomes reduced, making the integration more effective. Currently, some millimeter-wave applications include the wireless personal area network at 60 GHz, automotive radar at 77 GHz, and image sensing at 90 GHz.
A millimeter-wave frequency divider is typically included in a high-frequency phase-locked loop. Due to the high-speed capability and low-power characteristics, the injection-locked frequency divider is well suited for millimeter-wave operations. However, the division ratio (normally two) and locking range of millimeter-wave injection-locked frequency divider are inherently limited.
An injection-locked frequency divider design that would improve upon the conventional injection-locked frequency divider designs would be desirable in the art.
A representative injection-locked frequency divider includes a differential direct injection pair that is configured to receive and mix differential injection signals, and an oscillator that is electrically connected to the differential direct injection pair and produces an operating frequency based on the mixed differential injection signals.
The above and other features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention that is provided in connection with the accompanying drawings.
The accompanying drawings illustrate preferred embodiments of the invention, as well as other information pertinent to the disclosure, in which:
This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.
Exemplary systems are first discussed with reference to the figures. Although these systems are described in detail, they are provided for purposes of illustration only and various modifications are feasible.
In connection with the ILFD 125, it is beneficial to consider the frequency PLL circuit 100. PLL circuits can be executed using digital or analog circuits but will be explained generally with the understanding that the ILFD 125 may be applicable to both circuit types. The phase locked loop PLL 100 can start with phase detector 105. Such phase detector 105 generally compares two input signals—at a reference frequency and a feedback frequency—and produces an error signal that is proportional to their phase difference. The error signal is sent to a charge pump 110 that supplies charge in an amount proportional to the phase error detected.
A low-pass filter 115 receives the charge-represented phase error signal and filters the received phase error signal. The filtered signal drives a voltage-controlled oscillator (VCO) 120, which creates an output frequency. Such output frequency is fed through an injection-locked frequency divider (ILFD) 125 and a divide-by-N counter 130 back into the input of the phase detector 105, in a negative feedback loop. If the output frequency of the VCO 120 drifts up or down to a greater or lesser degree, the error signal can increase or decrease accordingly, driving the VCO frequency in the opposite direction so as to reduce the error. Thus the output is locked to the reference frequency, which can be derived from a crystal oscillator or other source (not shown).
Referring now to injection-locked frequency divider (ILFD) 125, the frequency of the input signal generally is a frequency of the free-running frequency of the oscillator 120. The input signal is then divided by the ILFD 125. The divided signal from the ILFD 125 is received by a divide-by-N counter 130.
This disclosure describes an ILFD 125 designed to increase the locking range without any tuning mechanism, which is an advantage according to the invention but can be a drawback for ILFDs currently available in the industry. Other advantages and improvements of the ILFD 125 will be apparent to those skilled in the art. The ILFD 125 is further discussed in
The divide-by-N counter 130 receives the divided signal from the ILFD 125 and generates an integer number of the divided signal. A non-integer number of the divided signal can be created by replacing the simple divide-by-N counter in the feedback path with a programmable pulse swallowing counter.
An improved embodiment compared to the divide-by-two ILFD 210 is a divide-by-three ILFD 220, which can address certain short-comings of the divide-by-two ILFD 210. One advantage, among others, of using the divide-by-three ILFD 220 is that output of the VCO 120 is applied to a balanced differential load rather than an unbalanced single-ended injection load. Also, assuming that the VCOs 205 or 215 are running at a given frequency, the divide-by-three ILFD 220 generates a lower frequency than the divide-by-two ILFD 210, which is desirable in this application. The remaining disclosure presents various designs of the divide-by-three ILFD 220 having advantageous aspects.
The divide-by-three ILFD 325 further includes an oscillator 310, 315, 350, 355, 340, 345 that is electrically connected to the differential direct injection pair 320, 327 and produces the output frequency based on the mixed differential injection signals. The oscillator can include a resonator 310, 315, 350, 355 and a cross-coupled transistor pair 340, 345. In this example, the resonator is implemented with inductors 310, 315 and parasitic capacitors 350, 355 from the cross-coupled transistor pair 340, 345 and the differential direct injection pair 320, 327, and the cross-coupled transistor pair 340, 345 can be implemented with NMOS-type transistors 340, 345.
The differential direct injection pair 320, 327 is electrically connected to the oscillator 310, 315, 350, 355, 340, 345 in a direct-injection scheme where the differential injection signals are injected into the input of the differential direct injection pair 320, 327. The differential direct injection pair 320, 327 can operate as switches to turned on and off the divide-by-three ILFD 325.
Frequency division happens as the differential direct injection pair 320, 327 converts the complementary or differential injection signals vI+ and vI− into differential currents, which mixes with the cross-coupled transistor pair 340, 345. The harmonics except the fundamental frequency are filtered out by the LC tank resonator formed by inductors 310, 315 and parasitic capacitors 350, 355. The even-order nonlinearity of the cross-coupled transistor pair 340, 345 can generate the desired mixing signal that corresponds to a division ratio of any odd number. In this example, the division ratio is 3 but ratio can be 5, 7, 9, 11 or any other odd numbers.
It should be noted that the NMOS-type transistors 320, 327, 340, 345 shown in the
Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention that may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.
