Oscillators – Plural oscillators – Parallel connected
Reexamination Certificate
1999-11-05
2001-04-17
Kinkead, Arnold (Department: 2817)
Oscillators
Plural oscillators
Parallel connected
C331S046000, C331S047000, C455S260000
Reexamination Certificate
active
06218908
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and apparatus for the injection lock of redundant oscillators, such as local oscillators in multichannel diversity receivers.
BACKGROUND OF THE INVENTION
Dual-diversity reception systems feature a pair of receivers configured to provide both diversity reception functionality, and redundancy such that should one of the receivers fail, the remaining receiver can take over thereby avoiding any loss of service. Such dual-diversity arrangements are common in wideband receivers.
There is a common relatively low frequency reference oscillator used by each receiver to drive the frequency of a respective much higher frequency local oscillator through a phase locked loop. Two independent higher frequency local oscillators are required for redundancy.
Diversity outputs are often combined using maximum ratio combining. It is important that the relative phase of the diversity outputs be somewhat constant within a burst for this maximum ratio combining to be effective. Using conventional phase locked loops avoids the requirement for complex custom multiloop phase locked loops. However, these phase locked loops utilize dividers with large local oscillator-to-reference frequency ratios, for example as large as 50000. This means that the high frequency oscillators in the two receivers are updated relatively infrequently, for example every 0.2 &mgr;s. The relative phases of the two local oscillators are thus allowed to drift relative to one another. The result is considerable phase jitter between the two oscillators' output frequencies even though they are derived from the same reference.
While it would be possible to have both receivers configured to exist on the same circuit board using a common oscillator, this defeats one of the advantages of having a diversity reception system, namely that protection is provided against single point failure. If one receiver fails, the remaining of the two receivers can continue to be used with some reduction in sensitivity. The fact that the two receivers are implemented on separate circuit boards further complicates the task of getting the oscillators to operate in phase.
SUMMARY OF THE INVENTION
It is an object of the invention to obviate or mitigate one or more of the above-identified disadvantages.
A broad aspect of the invention provides a coupled oscillator arrangement comprising first and second VCOs (voltage controlled oscillators), and a bi-directional interconnect which injection locks the first and second VCOs to each other. Advantageously, this provides a mechanism which effectively eliminates the phase jitter between the phase of first and second VCOs which makes them suitable for use in a diversity receiver, while at the same time providing a redundancy arrangement in which the failure of one of the VCOs does not effect the functionality of the other. The use of a bi-directional interconnect minimizes the complexity and cost of coupling the two VCOs.
Preferably, the bi-directional interconnect injects a first signal representative of an output signal of the first VCO to the output of the second VCO and injects a second signal representative of an output signal of the second VCO to the output of the first VCO.
Preferably, the bi-directional interconnect has a first coupler into which is coupled a first coupled signal which is a coupled portion of the output signal of the first VCO, a second coupler into which is coupled a second coupled signal which is a portion of the output signal of the second VCO, and a conductive path which conducts the first coupled portion to the output of the second VCO and simultaneously conducts the second coupled portion to the output of the first VCO.
The conductive path might for example be a first conductive portion from a first end of the first coupler to a first end of the second coupler, a second conductive portion from a second end of the first coupler to the output of the first VCO, and a third conductive portion from a second end of the second coupler to the output of the second VCO.
Signal isolation is preferably provided with a buffer arrangement consisting of a first buffer between the output of the first VCO and the first coupler, a second buffer between the output of the second VCO and the second coupler, a third buffer which buffers the signal connected to the output of the first VCO and a fourth buffer which buffers the signal connected to the output of the second VCO.
Typically, the first and second VCOs form part of respective receiver paths and have their respective support structures, for example respective printed circuit boards. The interconnect in such cases may include an interconnecting wire which physically connects the two separate printed circuit boards.
Furthermore, the first VCO would typically be part of a first phase locked loop and the second VCO would typically be part of a second phase locked loop. In such embodiments, a reference oscillator is connected to function as a reference for each of the first and second phase locked loops, typically through a divider circuit.
In some embodiments, it may be necessary or convenient to provide a phase adjust circuit, wherein the divided reference oscillator signal is passed directly to the first phase locked loop, and is passed to the second phase locked loop through the phase adjust circuit.
Embodiments also provide a receiver and a wide band receiver including such an oscillator arrangement.
Another embodiment provides a coupled oscillator arrangement comprising first and second VCOs (voltage controlled oscillators), and a first unidirectional interconnect which injection locks the first VCO to the second VCO and a second unidirectional interconnect which injection locks the second VCO to the first VCO.
REFERENCES:
patent: 4763085 (1988-08-01), Lamberg
Kinkead Arnold
Nortel Networks Limited
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