Patent Application
20090286490
The present invention relates to an oscillator circuit, and more particularly, to an oscillator circuit utilized in a transceiver, and a method for generating an oscillatory signal having a properly adjusted output frequency.
In general, a TX of a transceiver having a traditional oscillator circuit has a VCO pulling effect. The cause for the VCO pulling effect is usually due to the TX output signal coupled to the VCO, and the most probable cause is that the VCO frequency is a harmonic of the TX output frequency. The VCO pulling effect will cause performance degradation, such as phase noises, EVM, etc.
It is therefore one of the objectives of the present invention to provide an oscillator circuit utilized in a transceiver, and a method for generating an oscillatory signal having a properly adjusted output frequency, so as to solve the above problems.
In accordance with an embodiment of the present invention, an oscillator circuit for generating an oscillatory signal is disclosed. The oscillator circuit includes an oscillator, a frequency multiplier, a frequency divider, and a mixer module. The oscillator is utilized for generating a first signal having a first frequency. The frequency multiplier is coupled to the oscillator, and utilized for generating a second signal according to the first signal, wherein the second signal has a second frequency. The frequency divider is coupled to the oscillator, and utilized for generating a third signal according to the first signal, wherein the third signal has a third frequency. The mixer module is coupled to the frequency multiplier and the frequency divider, and utilized for mixing the second signal and the third signal to generate the oscillatory signal having an output frequency not being a harmonic of the first frequency.
In accordance with an embodiment of the present invention, a transceiver is further disclosed. The transceiver includes a local oscillator circuit for generating an oscillatory signal and a controlling circuit. The oscillator circuit includes an oscillator, a frequency multiplier, a frequency divider, and a mixer module. The oscillator is utilized for generating a first signal having a first frequency. The frequency multiplier has a programmable multiplier and is coupled to the oscillator, and utilized for generating a second signal according to the first signal, wherein the second signal has a second frequency. The frequency divider has a programmable divisor and is coupled to the oscillator, and utilized for generating a third signal according to the first signal, wherein the third signal has a third frequency. The mixer module is coupled to the frequency multiplier and the frequency divider, and is utilized for mixing the second signal and the third signal to generate the oscillatory signal having an output frequency being not a harmonic of the first frequency. The controlling circuit is coupled to the local oscillator circuit, and utilized for setting the programmable multiplier and the programmable divisor.
In accordance with an embodiment of the present invention, a method for generating an oscillatory signal is yet further disclosed. The method includes generating a first signal having a first frequency by an oscillator, generating a second signal according to the first signal by a frequency multiplier (the second signal having a second frequency), generating a third signal according to the first signal by a frequency divider (the third signal having a third frequency), and mixing the second signal and the third signal by a mixer module to generate the oscillatory signal having an output frequency being not a harmonic of the first frequency.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Certain terms are used throughout the following description and the claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “include”, “including”, “comprise”, and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “coupled” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
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The frequency multiplier 204 has a programmable multiplier M and is coupled to the oscillator 202, and is utilized for generating a second signal according to the first signal, wherein the second signal has a second frequency M*Fvco. The frequency divider 206 has a programmable divisor N and is coupled to the oscillator 202, and is utilized for generating a third signal according to the first signal, wherein the third signal has a third frequency Fvco/N. The mixer module 208 is coupled to the frequency multiplier 204 and the frequency divider 206, and is utilized for mixing the second signal and the third signal to generate the oscillatory signal, wherein the oscillatory signal has an output frequency (M±1/N)*Fvco. In addition, please note that the controlling circuit 110 in
In the first embodiment, the oscillator 202 includes an in-phase (I) output and a quadrature (Q) output, and the frequency multiplier 204 includes an I input coupled to the I output of the oscillator 202, a Q input coupled to the Q output of the oscillator 202, an I output, and a Q output. The frequency divider 206 includes an I input coupled to the I output of the oscillator 202, a Q input coupled to the Q output of the oscillator 202, an I output, and a Q output, and the mixer module 208 includes a first mixer 210 and a second mixer 212 each having a first input, a second input and an output. The I output from the frequency multiplier 204 is coupled to the first input of the first mixer, and the Q output from the frequency multiplier 204 is coupled to the first input of the second mixer. The I output from the frequency divider 206 is coupled to the second input of the first mixer, and the Q output from the frequency divider 206 is coupled to the second input of the second mixer.
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The frequency multiplier 304 has a programmable multiplier M and is coupled to the oscillator 302, and utilized for generating a second signal according to the first signal, wherein the second signal has a second frequency M*Fvco. The frequency divider 306 has a programmable divisor N and is coupled to the oscillator 302, and is utilized for generating a third signal according to the first signal, wherein the third signal has a third frequency Fvco/N. The mixer module 308 is coupled to the frequency multiplier 304 and the frequency divider 306, and is utilized for mixing the second signal and the third signal to generate the oscillatory signal, wherein the oscillatory signal has an output frequency (M±1/N)*Fvco. The subtractor 310 and the adder 312 are coupled to the mixer module 308. In addition, please note that the controlling circuit 110 in
In the second embodiment, the oscillator 302 includes an in-phase (I) output and a quadrature (Q) output; the frequency multiplier 304 includes an I input coupled to the I output of the oscillator 302, a Q input coupled to the Q output of the oscillator 302, an I output, and a Q output. The frequency divider 306 includes an I input coupled to the I output of the oscillator 302, a Q input coupled to the Q output of the oscillator 302, an I output, and a Q output. The mixer module 308 includes first, second, third, and fourth mixers 314, 316, 318, 320, each having a first input, a second input and an output. The I output from the frequency multiplier 304 is coupled to the first inputs of the first and third mixers 314, 318, and the Q output from the frequency multiplier 304 is coupled to the first inputs of the second and fourth mixers 316, 320. The Q output from the frequency divider 306 is coupled to the second inputs of the first and fourth mixers 314, 320, and the I output from the frequency divider 306 is coupled to the second inputs of the second and third mixers 316, 318. The outputs of the first and second mixers 314, 316 are coupled together via the subtractor 310, and the outputs of the third and fourth mixers are coupled together via the adder 312.
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Briefly summarized, since the first frequency Fvco (i.e., the VCO frequency) is not a harmonic of the output frequency (M±1/N)*Fvco, the VCO pulling effect can be avoided by utilizing the oscillator circuit, the transceiver, and the method of the prevent invention.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
