Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1998-12-09
2001-08-07
Kuntz, Curtis (Department: 2643)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S076000, C455S084000, C455S086000
Reexamination Certificate
active
06272329
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to full duplex transceiver systems and more particularly to frequency translation in transceiver systems involving bidirectional frequency translation.
2. Background of the Invention
Many radios are of the type that employ separate circuit stages for multiplexing and frequency translation for separating receive signals from transmit signals and for translating low frequency signals into radio frequency or high frequency bands. The use of separate circuit stages for multiplexing and frequency translation introduces a distortion in the form of phase error and group delay and distortion due to unwanted coupling. Additionally the use of separate circuit stages imposes a cost associated with the components used to implement the stages, and also imposes enclosure size limitations, power supply requirements and power dissipation considerations. In addition, the number of energy leakage paths in the system is determined by the number and placement of components.
Also, in a transceiver, frequency separation between transmit and receive frequencies is used to isolate separate transmit and receive frequency spectra. This is often accomplished using separate transmit and receive signal paths having respective up/down frequency translation stages. This leads to a redundancy in frequency translation components as similar components are used for each path. A reduction in components can be achieved by switching one up/down frequency translation stage selectively in and out of the transmit and receive paths but this defeats full duplex operation, reducing the system to half duplex operation only.
Thus, it would be desirable to achieve simultaneous up/down frequency translation in a single stage and reduce the number of circuit stages or reduce the number of components used in achieving multiplexing and frequency translation.
SUMMARY OF THE INVENTION
Embodiments of the present invention address the above needs by providing a bidirectional frequency translator apparatus and method in which transmit and receive spectra are simultaneously produced at both a low frequency port and a high frequency port of a mixer.
In accordance with one aspect of the invention, there is provided a method of frequency translation including receiving a first transmit signal at a low frequency port of a first mixer, up-converting the first transmit signal with the mixer to produce an up-converted first transmit signal at a high frequency port of the mixer, receiving a receive signal at the high frequency port, down-converting the receive signal at the mixer to produce a down-converted receive signal at the low frequency port and injecting the receive signal at the high frequency port while extracting the up-converted first transmit signal from the high frequency port.
The method may further include bandpass filtering a difference component of the up-converted transmit signal to produce a filtered difference component of the transmit signal and coupling the filtered difference component to an antenna system for transmission of the filtered difference component of the filtered difference signal.
The method may further include receiving and filtering a raw received signal from an antenna system to produce the receive signal.
When the method is implemented in a first radio or transceiver the method includes driving the mixer with a local oscillator signal having a frequency between a frequency spectrum of a difference component of the up-converted transmit signal and a frequency spectrum of the receive signal and when the method is implemented in a second radio or transceiver in communication with the first radio or transceiver, the method includes driving the mixer with a local oscillator signal having a frequency between a frequency spectrum of a sum component of the up-converted transmit signal and a frequency spectrum of the receive signal.
In accordance with another aspect of the invention, there is provided a frequency translator apparatus including a mixer and a duplexer. The mixer has a low frequency port and a high frequency port and is operable to receive a first transmit signal at the low frequency port and up-convert the first transmit signal to produce an up-converted first transmit signal at the high frequency port, while receiving a receive signal at the high frequency port and down-converting the receive signal to produce a down-converted receive signal at the low frequency port. The duplexer functions to inject the receive signal at the high frequency port while extracting the up-converted first transmit signal from the high frequency port.
Preferably, the apparatus includes a bandpass filter for bandpass filtering a difference component of the up-converted transmit signal to produce a filtered difference component of the transmit signal and includes an antenna system and a coupler for coupling the filtered difference component to the antenna system for transmission of the filtered difference component of the filtered difference signal. The coupler may include a final duplexer.
The apparatus may include components for receiving a raw received signal from the final duplexer and for filtering the raw receive signal to produce the receive signal.
Preferably, the apparatus includes a local oscillator for driving the mixer to produce a local oscillator signal having a frequency between a frequency spectrum of a difference component of the up-converted transmit signal and a frequency spectrum of the receive signal.
Another embodiment of the invention may include a local oscillator for driving the first mixer to produce a local oscillator signal having a frequency between a frequency spectrum of a sum component of the up-converted transmit signal and a frequency spectrum of the first receive signal.
In accordance with another aspect of the invention, there is provided a communication system including a first radio having a frequency translator apparatus as described above.
The communication system may further include a second radio having a second frequency translator apparatus including a second mixer and a second duplexer. The second mixer has a second low frequency port and a second high frequency port, and is operable to receive a second transmit signal at the second low frequency port and up-convert the second transmit signal to produce an up-converted second transmit signal at the second high frequency port, while receiving a second receive signal at the second high frequency port and down-converting the second receive signal to produce a second down-converted receive signal at the second low frequency port. The second duplexer injects the second receive signal at the second high frequency port while extracting the up-converted second transmit signal from the second high frequency port.
The second frequency translator apparatus includes a second local oscillator for driving the second mixer to produce a second local oscillator signal having a second frequency between a frequency spectrum of a sum component of the up-converted transmit signal and a frequency spectrum of the second receive signal.
In each of the above aspects the duplexer may be replaced with a coupler, a hybrid tee, or a circulator.
Effectively, embodiments the invention employ a single low frequency path and common mixer and uses the sum or difference mixing components in full duplex operation without the requirement to superheterodyne the low frequency or to use two or more mixers.
The use of a single bidirectional frequency transition stage eliminates the need to combine and divide the transmit low frequency signal and receive low frequency signal. Thus, multiplexing is automatically performed simultaneously with frequency translation. This reduces phase errors, group delays and distortions.
This also leads to a reduction of the number of components which improves reliability, reduces costs and reduces power dissipation. The number of components is reduced because the single local oscillator drives only one port and therefore requires less drive capability than
Kuntz Curtis
Nortel Networks Limited
Taylor Barry W
LandOfFree
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