Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
2002-10-04
2004-08-31
Appiah, Charles (Department: 2686)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S313000, C455S118000, C375S298000
Reexamination Certificate
active
06785528
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to electronic communication devices and, more particularly, to a circuit for providing a divided quadrature signal.
2. Description of the Related Art
Wireless communications devices are continuously being updated for smaller size, greater battery life and lower cost. One important factor in achieving these goals is greater integration of the electronics used in a wireless communications device. In many devices, such as mobile phones, it is envisioned that the entire electronics will be integrated onto a single chip in the near future.
In order to achieve the highest possible level of integration, a homodyne transmitter design may be used. One of the major issues with this design is on-chip generation of quadrature signals from the transmit VCO (voltage controlled oscillator). The quadrature signals should have a very low close in phase noise as well as a very low noise floor, on the order of −165 dBc at a 20 MHz offset. By dividing the signal frequency in two, a 6 dB gain in close-in phase noise can be obtained. Presently, signal division is generally performed using latches to divide the signal and generate quadrature signals. Unfortunately, in using latches to produce the quadrature signals, a noise floor of −145 dBc is about the best that can be achieved.
Therefore, a need has arisen for a low-noise solution for generating a divided quadrature signal.
BRIEF SUMMARY OF THE INVENTION
In the present invention, a quadrature divider includes a first analog mixer for receiving a digital input signal at a predetermined frequency at a first input of the first mixer and a second analog mixer for receiving the input signal with a 180° phase shift at a first input of the second mixer. The output of the first mixer is coupled to a second input of the first mixer and an output of the second mixer is coupled to a second input of the second mixer.
The present invention provides significant advantages over the prior art. A quadrature signal at one-half of the input frequency is obtained, without the noise associated with the use of latches to obtain the divided signal. In a differential embodiment, the 180° phase shift between inputs to the mixers can be obtained by a polarity inversion at the inputs to one of the mixers, thereby eliminating any unwanted delays associated with the phase shift.
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Ferre-Pikal, et al., “Microwave Regenerative Dividers With Low Phase Noise”, Microwave Symposium Digest, !998 IEEE MTT-S International, Jun. 1998, vol. 3, pp. 1447-1450.*
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Appiah Charles
Neerings Ronald O.
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