Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Phase shift by less than period of input
Reexamination Certificate
2003-05-05
2004-06-01
Nguyen, Linh M. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Phase shift by less than period of input
C327S246000
Reexamination Certificate
active
06744296
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to phase-shift circuits. More specifically, the present invention provides circuits and methods for accurately shifting the phase of a signal by any programmed amount.
BACKGROUND OF THE INVENTION
A phase-shift circuit is one whose sole purpose is to shift the phase of an input signal to produce an output signal that is but of phase with the input signal. Two signals are out of phase when there is a relative displacement between the signals at a given point in time. For example, signals A and B shown in
FIG. 1
are 90° out of phase. A is said to lead B by 90°, and, conversely, B is said to lag A by 90°. A simple phase-shift circuit such as shown in
FIG. 2
may be used to shift an input signal by a certain degree depending on the value of resistor
25
, capacitor
30
, and the frequency of the input signal to generate a phase-shifted output signal.
Phase-shift circuits are useful in a number of diverse applications, including phase detection, modulation, high power and high frequency amplification, and voltage regulation involving multiple paralleled power supplies, among others. In these and most other applications, phase-shift circuits are used to provide a phase difference based on which other signals are generated or controlled.
For example, a phase-shift circuit is often used in combination with a phase detector circuit to provide a DC output voltage proportional to the phase difference between its input signals. A well-known phase detector circuit is the quadrature detector widely used in many communications applications, and in particular, in applications involving quadrature amplitude modulation and phase modulation. The quadrature detector uses a phase-shift circuit to provide quadrature input signals, i.e., input signals that are spaced 90° apart, to a phase detector. The phase detector produces different output voltages for different phase shifts to recover the modulation.
Examples of phase-shift circuits designed for communications applications include those described in U.S. Pat. No. 4,355,289, U.S. Pat. No. 4,549,152, U.S. Pat. No. 5,317,288, and U.S. Pat. No. 5,317,276. Such circuits either provide a limited number of phase shifts, e.g., multiples of 90°, or require a complex control signal or a control circuit to set the phase shift.
Phase-shift circuits may also be used to maintain phase linearity in high power, high frequency amplifiers as described in U.S. Pat. No. 4,581,595, and to control the phase of video signals transmitted according to the NTSC (National Television System Committee) and PAL (Phase Alternation by Line) standards, as described in U.S. Pat. No. 5,317,200. Similar to the phase-shift circuits designed for communications applications, these phase-shift circuits only provide a limited number of phase shifts.
Another application in which phase-shift circuits are useful is in voltage regulation involving multiple paralleled power supplies. A voltage regulator is a device that produces a predetermined and substantially constant output voltage from a source voltage that may be poorly-specified or fluctuating, or that may be at an inappropriate amplitude for the load.
One type of a commonly-used voltage regulator is a switching voltage regulator. Switching voltage regulators employ one or more power devices as the switching elements and inductors, transformers, and capacitors as energy storage elements between the source and the load. The switching elements may be, for example, power metal-oxide semiconductor field-effect transistor (MOSFET) devices. A switching voltage regulator regulates the voltage across the load by varying the ON-OFF times of the switching elements so that power is transmitted through the switching elements and into the energy storage elements. The energy storage elements then supply this power to the load so that the load voltage is regulated.
Multiple switching voltage regulators are often paralleled together in a single system to produce multiple disparate output voltages or to produce a higher output current. In this case, it is preferable to have all switching voltage regulators synchronized to the same operating frequency. Proper application of synchronization consolidates the spectral content of the noise in the system due to the use of multiple regulators, reduces noise filtering requirements, and eliminates the enharmonic hetrodynes in the system, i.e., the “beat frequencies” arising from the sum of and difference between the different frequencies of the multiple regulators.
In addition to synchronization, it is also desirable to have multiple switching voltage regulators interleaved when they are sharing the same input rail. An interleaved system employs a phase-shift circuit to provide a constant phase difference between any two regulators, i.e., the phase difference between any two regulators is constant regardless of changes in other operating parameters. The phase difference between any two regulators depends on the number of regulators (or phases) in the system, e.g., 180° (360°/2) for a two-phase system, 120° (360°/3) for a three-phase system, 90° (360°/4) for a four-phase system, 72° (360°/5) for a five-phase system, etc.
When properly interleaved, the system input RMS current is minimized and the frequency of the input ripple current is effectively multiplied, thereby enabling the use of a smaller input capacitor and reducing the power loss that arises from resistances in fuses, printed circuit board traces, connectors, input capacitance equivalent series resistances (“ESRs”), among others. Further, when multiple switching voltage regulators are interleaved to provide a single output, the steady-state output ripple voltage is significantly reduced and the dynamic load transient response is significantly improved over a non-interleaved configuration. Examples of control integrated circuits for multiple interleaved switching regulators include LTC1628, LTC1629, and LTC3728, provided by Linear Technology Corporation, of Milpitas, Calif. These switching regulator controllers employ two switching regulators to produce one (LTC1629) or two (LTC1628, LTC3728) regulated outputs.
To provide a multi-phase interleaved system, it is necessary to use phase-shift techniques or phase-shift circuits between any two switching regulators. One approach that does not require any additional phase-shift circuitry between two regulators involves using the inherent phase-shifted signal from the first regulator to synchronize the internal clock of the second regulator. For example, in a synchronous Buck converter, the bottom gate drive signal of the first regulator, i.e., the signal that drives the bottom switching element of the first regulator, is used to synchronize the internal clock of the second regulator.
This approach suffers from two major drawbacks. First, when the first synchronous Buck regulator is subjected to load or line changes, its bottom gate signal shifts in phase, thereby introducing a temporary frequency deviation in the second regulator. That is, the phase difference between the first regulator and the second regulator is not constant with varying load or voltage levels. Second, the phase difference between the first regulator and the second regulator is fixed by the duty cycle of the fist regulator and is usually not optimized. With many switching voltage regulators having different duty cycles at different operation modes, e.g., continuous current mode, discontinuous current mode, and other power-savings modes, this approach does not guarantee constant phase differences between the two regulators or does not work when the bottom gate of the first regulator is turned off during a power-savings mode.
Another approach that may be used to provide a phase difference between two regulators is to apply the gate drive signal of the first regulator, i.e., the signal that drives the switching element of the first switching voltage regulator, as input to R-C circuit
20
shown in
FIG. 2
to synchronize the internal clock of the second switching voltage regulator.
Chen Yuhui
Hobrecht Stephen W.
Lee Mitchell E.
Fish & Neave
Higgins Gabrielle E.
Linear Technology Corporation
Nguyen Linh M.
Rowland Mark D.
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