Offset signal phasing for a multiple frequency source system

This patent application is related to, and concurrently filed with each of the following patent applications, the contents of which are herein incorporated by reference for all purposes:

“Multiple Frequency Source System and Method of Operation,” application Ser. No. 11/461,530, and

“System and Method for Mitigating Phase Pulling in a Multiple Frequency Source System,” application Ser. No. 11/461,534.

This patent application claims priority to, and incorporates in its entirety each of the following US patent applications:

“Multiple Frequency Source System and Method of Operation,” Application Ser. No. 60/595,754, filed Aug. 2, 2005;

“Offset Signal Phasing for a Multiple Frequency Source System,” Application Ser. No. 60/595,749, filed Aug. 2, 2005; and

“System and Method for Mitigating Phase Pulling in a Multiple Frequency Source System,” Application Ser. No. 60/595,750, filed Aug. 2, 2005.

The present invention relates to tunable systems employing concurrently operable frequency sources, and in particular to offset signal phasing for use with said system.

The implementation of multiple frequency sources in a system, as described in the application entitled “Multiple Frequency Source System and Method of Operation,” presents possible challenges in how to control the system's power consumption. Specifically, the operation of multiple frequency sources may create a high peak current demand from the power supply, possibly resulting in a drop in the power supply voltage to a level which may be insufficient to continue reliable system operation.

What is therefore needed is a system and method for avoiding high peak current consumption in a system employing multiple frequency sources.

Systems and methods are presented herein for avoiding high peak power (current or voltage) consumption in a multiple frequency source system through the use of phase delays to stagger the application of input signals to respective frequency sources.

In an exemplary embodiment, the multiple frequency source system includes a first operating frequency source, a phase delay element, and a second operating frequency source configured to operate concurrently with the first frequency source. The first frequency source includes an input coupled to receive a reference input signal and an output for providing a first frequency source signal. The phase delay includes an input coupled to receive the input reference signal, and an output, the phase delay element operable to apply a predefined phase delay to the input reference signal to produce a phase-delayed input signal. The second frequency source includes an input coupled to receive the phase-delayed input signal and an output for providing a second frequency source signal.

These and other features of the invention will be better understood when viewed in light of the following detailed description and drawings.

FIG. 1A illustrates a tunable system employing multiple frequency sources, whereby the operating frequency sources are operating coherently.

FIG. 1B illustrates time domain signal waveforms and peak current consumption for the tunable multiple frequency source system of FIG. 1A .

FIG. 2A illustrates an exemplary multiple frequency source system employing offset signal phasing in accordance with the present invention.

FIG. 2B illustrates an exemplary method for operating a multiple frequency source system in accordance within one embodiment of the present invention.

FIG. 2C illustrates time domain signal waveforms and peak current consumption for the system of FIG. 2A using the method of FIG. 2B

FIG. 3 illustrates an exemplary implementation of the phase delay elements used to provide offset signal phasing in the tunable multiple frequency source system of FIG. 2A .

FIG. 4 illustrates an exemplary block diagram of a regulated power supply for use with the tunable multiple frequency source system of FIG. 3A .

For clarity, previously identified features retain their reference indicia in subsequent drawings.

FIG. 1A illustrates a tunable system employing concurrently operating frequency sources (“tunable multiple frequency source”), whereby the operating frequency sources are operating in a high current mode coherently. The system 100 includes n frequency sources 130 1,n , which in a particular embodiment, includes at least one tunable source, such a variable frequency oscillator or phase locked loop. One or more of the remaining frequency sources may be tunable or fixed frequency sources.

During operation, the system receives an input signal 110 which is supplied to two or more (all, as illustrated) of the operating frequency sources 130 1,n . The input signal 110 is operable to initiate a high current mode of operation, which may comprise activating the frequency source to generate an output signal F S1,n . In exemplary embodiments, the input signal 110 may be a clock signal, a reference signal, or other such signal operable to activate the frequency sources, or to otherwise produce a high current mode of operation such that the frequency source begins to draw a significant amount of current (e.g., more than 50 percent of its maximum current handling capacity).

FIG. 1B illustrates time domain signal waveforms and peak current consumption for the tunable multiple frequency source system of FIG. 1A . As shown, multiple frequency sources are activated, and accordingly, enter into a high current mode of operation substantially concurrently. As a result, the power supply bus is subjected to very high current supply spikes. This condition creates undesired effects, in that the power supply may not have sufficient capacity to supply the high peak current needed during these periods, resulting in a drop in the supply voltage to a level which may not be sufficient to continue reliable system operation. Furthermore, the generation of the high current spikes in the time domain is accompanied by a large number of spurious products in the frequency domain. The presence of a large number of spurious products on the power supply bus is especially problematic, as the power supply bus structure provides a signal path to each of the frequency sources 130 1,n , where the spurs can combine with desired output signals F S1,n to degrade the phase noise of the intended output signals F S1,n .

FIG. 2A illustrates an exemplary tunable multiple frequency source system employing offset signal phasing in accordance with the present invention. The system includes n frequency sources 230 1,n operable to generate n corresponding frequency source signals F Sn , and n−1 phase delay elements 220 1,(n−1) . An input signal 210 is operable to activate, or otherwise cause the coupled frequency sources 230 1,n to enter into a high current mode.

As shown, the n−1 phase delay elements 220 1,n are interposed between adjacent frequency sources, wherein one of the frequency sources (illustrated as frequency source 2 , 230 2 ) receives an undelayed version of the input signal 210 (referred to herein as the reference input signal) and operates as a reference frequency source. Each of the n−1 phase-delay elements 220 is operable to apply a particular predefined phase offset φ 1,(n−1) to the incoming signal, thereby producing n−1 delayed input signals 225 . The calculation of the predefined phase offsets the calculation of which is further described below. By computing a phase offset and applying said offset to the frequency sources via the phase delay elements 220 , current consumption of the frequency sources can be staggered, and the undesirable conditions of a drop in the power supply voltage or spurious product generation can be mitigated.

The phase delay may be provided electrically, i.e., through the use of a particular structure such as an inverter, or physically, through the implementation of a number of cascaded elements (e.g., inverters) that provides a time delay equivalent to the desired phase delay. The system 200 may be implemented in “ladder” type network arrangement in which the phase delay at the input of the nth frequency source 230 n is the sum of delay elements 220 2 to 220 n . Alternatively, a “star” type network may be employed in which each delay element 2201 , 2 receives the system input signal 210 , and only one delay element is used to apply the desired delay prior to input to the corresponding frequency source 230 . Further alternatively, the system may employ segments of both types of structures, as shown in the illustrated embodiment of FIG. 2A .

FIG. 2B illustrates an exemplary method for operating a tunable multiple frequency source system in accordance within one embodiment of the present invention. Initially at 262 , a reference frequency source (e.g. source 230 2 ) is identified from the plurality of frequency sources. The signal input into the reference frequency source is defined as having a relative phase offset of zero degrees in the following phase offset computation process.

At 264 , the phase offsets for each of the remaining n−1 signals which are input into the corresponding n−1 frequency sources are computed. In one embodiment of this process, the reference signal, and the remaining n−1 input signals are spaced equally apart over a phase range provided by the calculation:

n - 1 n × 360 = phase ⁢ ⁢ range eq . ⁢ ( 1 )

where n is the number of concurrently operating frequency sources.

For example, in a system embodiment in which three frequency sources are implemented, the reference input signal is located at 0 degrees, and the first and second phase-delayed signals are located at 120 and 240 degrees phase.

In another embodiment, the reference input signal and the remaining n−1 phase-delayed signals are spaced equally apart over a 180 degree phase range. For example, in a system embodiment in which three frequency sources are implemented, the reference input signal is located at 0 degrees, and the first and second phase-delayed signals are located at 90 and 180 degrees phase.

At 266 , the phase offsets computed for the respective n−1 input signals are applied to their corresponding input signals to provide the desired phase delay. In a particular embodiment of this process, one or more of the n−1 input signals are transmitted through an odd number (2n+1) of inverters cascaded to provide a 180 degree phase shift relative to an even number (2n) of cascaded inverters which may be used to provide the reference input signal. In a further embodiment, one or more of the n−1 input signals are transmitted through a cascaded string of circuit elements (e.g., inverters) operable to provide a physical time delay which provides the desired phase delay. A combination of these approaches may be used to provide the necessary phase delay elements, as further illustrated below.

FIG. 2C illustrates time domain signal waveforms and peak current consumption for the system of FIG. 2A using the method of FIG. 2B . The responses are shown for a system consistent with FIG. 2A employing three concurrently operation frequency sources which provide output frequencies F S0 , F S1 and F S2 , respectively. The system includes a first phase delay element φ 1 which generates a 180 degree phase-shifted delayed input signal 225 1 , that signal 225 1 being supplied to its corresponding frequency source 230 1 to produce an output waveform F S1 . Further included is a second phase delay element 100 2 which generates a 90 degree phase-shifted delayed input signal 225 2 , that signal 225 2 being supplied to its corresponding frequency source 230 3 to produce an output waveform FS 3 .

As the time domain waveforms show, the rising edges of F S1 , F S2 , F S3 are offset 90 degrees from each other. The offset phasing produces a distributed peak current response compared to the response in FIG. 1 , resulting in reduced current peaking and less spurious product generation.

As noted above, one or more of the concurrently operating frequency source 230 1,n will be a tunable source, an example of which is a sigma-delta fractional phase locked loop circuit. The remaining frequency sources may be tunable or fixed frequency, as dictated by the design. In the particular embodiment in which the frequency source is a phase locked loop, the phase-delay element associated therewith may be located along the signal path supplying the loop's reference signal F Ref .

FIG. 3 illustrates an exemplary implementation of the phase delay elements used to provide offset signal phasing in system of FIG. 2A . The phase delay element φ 1 220 1 includes three inverter elements 310 1 , 310 2 and 310 3 , this number representing one inverter more than the total number of inverter elements 320 1 and 320 2 provided for the reference input signal 225 2 . In this embodiment, the two inverter delay elements 310 1 and 310 2 are used to provide an input buffer to the input of the reference frequency source 230 2 receiving the reference input signal 225 2 , and the additional inverter element 310 3 supplied in the phase delay element 220 1 provides a 180 degree phase relative to the reference input signal 225 2 . In an alternative embodiment, fewer inverter elements may be used (e.g., no inverters used for the reference input signal 225 2 and one inverter element for producing the delayed input signal 225 1 ), or more inverter elements may be used (e.g., 2n inverters used for generating the delayed input signal 225 1 , and 2n+1 inverters used for generating the reference input signal 225 2 ).

Phase delay element φ 2 220 2 is realized in a particular embodiment using multiple, series-coupled inverter elements 330 1,m , the collective arrangement of which produces the desired time/phase delay. In one embodiment, the desired delay is substantially midway between the phasing of the existing reference and delayed input signals 225 1 and 225 2 ; for example in the above illustrated embodiment in which reference and delayed input signals 225 1 and 225 2 are located at 0 and 180 degree relative phasing, a sufficient number of inverter elements 330 1,m is cascaded to provide a time/phase delay substantially equivalent to 90 degrees of phase delay. For example, a cascaded arrangement of 150-200 inverter elements may be needed to provide the physical delay. As the inverter elements are quite small in size, have high associated yield, and are easily producible, a large number can be easily implemented within an integrated circuit without difficulty.

FIG. 4 illustrates an exemplary block diagram of a regulated power supply (“regulator” herein) for the tunable multiple frequency source system of FIG. 3A . The regulator 400 includes an operation amplifier OP 1 410 , a transistor T 1 420 , feedback resistors R 1 and R 2 430 , regulator capacitor C 1 440 , and a power supply bus 450 . The operational amplifier 410 is connected in a conventional non-inverting amplifier configuration and includes a non-inverting input coupled to receive a reference voltage and a resistive divider formed by resistors 430 a and 430 b coupled to the inverting input. The regulator capacitor 440 is operable to filter out ac signals propagating along the power supply bus 450 and provides charge to the power supply bus 450 when supply transistor 420 is in a cutoff mode. Supply transistor 420 (exemplary illustrated as a bipolar junction transistor) includes a collector terminal coupled to the unregulated power supply, a base terminal coupled to the output of the operational amplifier 410 , and an emitter terminal coupled to the power supply bus 450 .

When the reference sources toggle, the supply transistor 420 and regulator capacitor 440 supplies the required current. Due to the limited bandwidth of the regulator (especially if it is providing a very low amount of DC current) the peak current is provided by the regulator capacitor 440 from the charge stored thereby, with a consequential drop of the regulated voltage. After the time delay dependent on the regulator bandwidth, the regulator restores the charge in the regulator capacitor 440 , bringing the regulated voltage to steady state value. In the low current conduction, the lower value of the peak current supplied at higher frequency acts as low pass filtering of the peak current that needs to be supplied in high current mode. Consequently the voltage ripple on the regulated voltage is reduced.

As readily appreciated by those skilled in the art, the described processes may be implemented in hardware, software, firmware or a combination of these implementations as appropriate. In addition, some or all of the described processes may be implemented as computer readable instruction code resident on a computer readable medium (removable disk, volatile or non-volatile memory, embedded processors, etc.), the instruction code operable to program a computer of other such programmable device to carry out the intended functions.

The terms “a” or “an” are used to refer to one, or more than one feature described thereby. Furthermore, the term “coupled” or “connected” refers to features which are in communication with each other (electrically, mechanically, thermally, as the case may be), either directly, or via one or more intervening structures or substances. The sequence of operations and actions referred to in method flowcharts are exemplary, and the operations and actions may be conducted in a different sequence, as well as two or more of the operations and actions conducted concurrently. All publications, patents, and other documents referred to herein are incorporated by reference in their entirety. To the extent of any inconsistent usage between any such incorporated document and this document, usage in this document shall control.

The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the disclosed teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.