Demodulation of an intermediate frequency signal by a sigma-delta converter
AssigneeNokia Mobile Phones Ltd.
InventorsJaakko A. Hulkko, Veijo L. H. Kontas, Lauri T. Siren
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Abstract
A sigma-delta signal converter is implemented using switched capacitor switching elements in which a first switch (31) serves as a mixer (11). The output of the mixer is directed to the second input of an adder (16), and its second input is the feedback signal (f1) of the sigma-delta signal converter, which is also directed into a base-frequency output signal through a decimator (14) and low-pass filtering (15).
Claims16
A receiver for receiving a modulated carrier signal comprising, a sigma-delta signal converter having at least one summing node included in a feedback loop, characterized in that the sigma-delta signal converter comprises a time discrete sampling means located at an input stage of the sigma-delta signal converter controlled by a square wave local oscillator signal for down converting the received modulated carrier signal to a base-band signal, wherein the frequency of the square wave local oscillator signal is equal to one of the carrier signal frequency of the received modulated carrier signal plus an offset frequency .DELTA.f, where .DELTA.f is equal to one of a value of zero or a value greater than zero, or a subharmonic of the modulated carrier signal frequency.
A circuit for receiving a modulated radio frequency (RF) carrier signal for down converting the received carrier signal to a base-band signal, the circuit comprising a sigma-delta signal converter circuit comprised of a switched capacitor input stage that is switched with local oscillator signal provided in the form of a non-sinusoidal switching signal having a frequency equal to or approximately equal to one of a frequency of said received carrier signal, or a sub-harmonic of said received carrier signal;
- said switched capacitor input stage outputting the base-band signal;
- a first summing node having a first input coupled to an output of said input stage;
- a first integrator coupled to an output of said first summing node;
- a second summing node having a first input coupled to an output of said first integrator;
- a second integrator coupled to an output of said second summing node;
- and a comparator coupled to an output of said second integrator;
- wherein an output of said comparator is coupled back to a second input of each of said first summing node and said second summing node;
- said sigma-delta signal converter circuit further comprising a decimator coupled to an output of said comparator and a filter coupled to an output of said decimator.
In a radio telephone, a method for converting a received modulated intermediate frequency (IF) signal to a base-band signal, comprising the steps of:
- applying the IF signal to an input stage of a sigma-delta converter circuit, the input stage comprising a switched capacitor circuit;
- mixing the IF signal to the base-band signal in the switched capacitor circuit by applying a switch control local oscillator (LO) signal having a frequency equal to one of the frequency of the received modulated IF signal plus or minus an offset frequency .DELTA.f, where .DELTA.f is equal to one of a value of zero or a value greater than zero, or a subharmonic of the received modulated IF signal;
- and
- demodulating and converting an output of the switched capacitor circuit to a digital signal by the sigma-delta converter circuit.
Dependencies are inferred from the claim text.