Direct conversion receiver
AssigneeU.S. Philips Corporation
InventorRishi Mohindra
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Abstract
A direct conversion receiver, such as a paging receiver includes a local oscillator for mixing down to baseband a received radio frequency signal having a carrier frequency which is digitally modulated (FSK). To provide automatic frequency control, instead of using a control loop, the present invention includes means which at intervals evaluates the recovered digital signal to determine whether a predetermined quality thereof is within a selected D/A conversion range. A microcontroller including a D/A converter generates a control signal for the local oscillator to maintain the oscillator at a frequency such that the signal quality remains within the selected conversion range.
Claims20
A direct conversion receiver comprising a local frequency generating arrangement which is coupled to a pair of quadrature related mixers for mixing down a radio frequency input signal (rf) to derive quadrature related signals (I, Q), a demodulator for demodulating the quadrature related signals into demodulated data (dta), and automatic frequency control (a.f.c.) means for providing a control signal (ct) for the local frequency generating arrangement, the a.f.c. means being coupled to quadrature paths;
- characterized in that the a.f.c. means comprise a digital-to-analog conversion arrangement for providing the control signal (ct), signal quality determining means for determining a valid data signal (vdta) from the demodulated data (dta), storage means for storing a valid data range (VR) during data scanning intervals, and means for adjusting an output signal of the digital-to-analog conversion arrangement to an adjustment value within the valid data range (VR).
Dependencies are inferred from the claim text.