Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1999-09-03
2001-11-27
Nguyen, Lee (Department: 2746)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S285000
Reexamination Certificate
active
06324388
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image reject mixer circuit arrangements and in particular, although not exclusively, to image reject mixer circuit arrangements for use in radiotelephone RF receiver circuits.
BACKGROUND OF THE INVENTION
There is a continuing drive in radiotelephone receiver design to improve the linearity characteristics, the power consumption and the noise figure of the receiver circuitry whilst achieving a suitable level of receiver gain. Image reject mixer circuits are commonly used circuit blocks of such receivers. Image reject mixer circuits in which RF input signals are arranged to be fed into first and second parallel paths, associated with in-phase and quadrature local oscillator signals respectively, and subsequently combined are generally preferred to mixer circuits which have a filter to reject image frequency signals. This preference stems from the fact that their noise figure is comparable to that obtained when an ideal image reject filter is used, which of course is not possible, and they tend to take up less chip area and/or involve fewer discrete components than mixer circuits having image reject filters. Whatever type of image reject mixer circuit is used in a radio receiver, its parameters determine the main characteristics of the receiver.
BRIEF SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided an image reject mixer circuit arrangement in which input signals are arranged to be fed into first and second parallel paths, associated with in-phase and quadrature local oscillator signals respectively, and subsequently combined comprising in each path a current signal source circuit arranged to provide from first and second outputs thereof differential current signals, dependent on the input signals, to a mixer stage characterized in having a capacitor connected between the first outputs of the current signal source circuits of the first and second paths.
In accordance with a second aspect of the present invention, there is provided an image reject mixer circuit arrangement comprising:
an input;
first and second current signal source circuits each having an input and first and second outputs;
first and second mixer stages each having first and second signal inputs, a local oscillator signal input and first and second outputs;
a combiner circuit having first to fourth inputs and an output;
a capacitor having first and second electrodes; and
an output;
the input being connected to the first current signal source circuit input and to the second current signal source circuit input, the first current signal source first and second outputs being connected to the first mixer stage first and second signal inputs respectively, the second current signal source first and second outputs being connected to the second mixer stage first and second signal inputs respectively, the first mixer stage first and second outputs being connected to the combiner circuit first and second inputs respectively, the second mixer stage first and second outputs being connected to the combiner circuit third and fourth inputs respectively, the combiner circuit output being connected to the output, the capacitor first electrode being connected to the first current signal source circuit first output and the capacitor second electrode being connected to the second current signal source circuit first output.
The current signal source circuits are preferably transconductors but may alternatively be current amplifiers, phase splitters or the like. The primary requirement is that they provide differential current signals dependent on the input signals to their respective mixer stage.
REFERENCES:
patent: 5033110 (1991-07-01), Harman
patent: 0782249 A1 (1996-12-01), None
patent: 2239143 A (1989-12-01), None
Kilpatrick & Stockton LLP
Mitel Semiconductor Limited
Nguyen Lee
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