Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1998-09-23
2001-08-21
To, Doris H. (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S304000, C455S307000, C455S334000, C455S340000
Reexamination Certificate
active
06278870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to phasing receivers and particularly, but not exclusively to polyphase or sequence-asymmetric receivers which may be implemented as an integrated circuit.
2. Description of the Related Art
A popular type of architecture for use as an integrated receiver is a zero-IF architecture in which an input signal is frequency downconverted to a zero-IF using quadrature mixers, the wanted signals are selected from the products of mixing using low pass filters and the wanted signals are processed further to provide a demodulated output.
Most of the limitations which beset the zero-IF receiver arise either directly or indirectly from the fact that components of wanted signals translated down to IF frequencies at or around DC cannot be distinguished from components of unwanted signals which appear in the same frequency range as a result of inherent circuit deficiencies.
The above-mentioned limitations in a zero-IF receiver may be eliminated substantially in a low-IF superheterodyne receiver but this would suffer from an image response that could not be eliminated by realistic front-end filters.
Another receiver architecture termed a phasing receiver, is a low-IF receiver based on the principle of the image-reject mixer in which the image response is removed by cancellation, rather than filtering, but the level of image rejection which can be achieved, even in fully-integrated form, is severely limited by the degree of matching which can be obtained between nominally identical components. A particular example of a phasing receiver is the polyphase or sequence-asymmetric receiver in which the conventional IF filters, IF phase shifters and IF signal combiner are replaced by a single polyphase IF filter. This very substantially increases the level of image rejection which can be obtained. In spite of the increased level of image rejection there may still a need to improve further the level of image rejection.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to improve the image rejection capability of a phasing receiver.
According to one aspect of the present invention there is provided a phasing receiver having a polyphase or sequence-asymmetric gyrator filter in which lack of image rejection is improved by the fine adjustment of the phase and/or amplitude of input signals.
According to a second aspect of the present invention there is provided a phasing receiver comprising an input, first and second signal mixing means for providing quadrature related low IF frequencies, a polyphase filter having inputs coupled to outputs of the first and second signal mixing means and signal demodulating means coupled to outputs of the polyphase filter, and means for effecting fine adjustment of the phase and/or amplitude of signals applied to the inputs of the polyphase filter to compensate for less than optimum image rejection.
By means of the present invention fine adjustment of the amplitude and/or phase of the pair of IF signals feeding a polyphase IF filter can further improve the level of image rejection which can be obtained, typically by at least 10dB.
REFERENCES:
patent: 4723318 (1988-02-01), Marshall
patent: 6035186 (2000-03-01), Moore et al.
patent: 0344852 (1989-12-01), None
patent: 0 576 082 (1993-12-01), None
Davie Alan J.
Moore Paul A.
Slobod Jack D.
To Doris H.
U.S. Philips Corporation
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