Patent ID: 6891908

Claim:
A portable radio system comprising: an internal oscillator; and an automatic frequency control for detecting a frequency shift of said internal oscillator with reference to a received wave transmitted from a base station and adjusting a frequency of said internal oscillator by feeding back said frequency shift to said internal oscillator, wherein coordinate rotation digital computation (CORDIC) is employed for calculation of arctangent in said automatic frequency control; and wherein, upon performing calculation said detecting of said frequency shift comprises deriving parameters CORDICi and CORDICq said coordinate rotation digital computation, where a signal whose phase is to be calculated is replaced with I and Q components of said signal, and in calculation of said coordinate rotation digital computation, when a parameter for outputting a final angle by adding angles per taps is set as phase, a process expressed by: when CORDICi<0.0 and CORDICq<0.0 CORDICi=CORDICq CORDICq=CORDICi*−1.0 phase=π/2 when CORDICi<0.0 and CQRDICq<0.0, CORDICi=CORDICq*−1.0 CORDICq=CORDICi phase=−(π/2) is performed.